Electronic system for a field device that is fed by an external electric energy supply

Translation of description of equivalent WO 2006072541 A2

p0001description

p0002fed from an external electric power supply

p0003Field-device electronics

p0004[0001] The invention relates to a fed from an external electrical power supply field-device electronics for a field device and a field device with such a field-device electronics.

p0005[0002] In the industrial process measuring technology, esp. In connection with the automation of chemical or industrial processes and / or the control of industrial equipment, for the production of process variables analog or digital representing measured-value signals on site, ie close to the process installed instruments, so called field devices used. Similarly, field devices may be formed as one or more of such process variables and changing the extent engaging into the process actuators. In the area to capture each and discontinuing process variables may be, for example, as well as above-mentioned prior art can be removed to a mass flow, a density, a viscosity, a filler or a limit level, a pressure or a temperature or the like, a liquid, powdered, vaporous or act gaseous medium, which is in an appropriate container such as a pipe or a tank, guided or held. Further examples of such to the person skilled in itself known field devices are described in WO-A 03/048874, WO 02/45045, WO-A 02/103327, WO-A 02/086426, WO-A 01/02816, WO-A 00/48157, WO-A 00/36 379, WO-A 00/14 485, WO-A 95/16 897, WO-A 88/02 853, WO -A 88/02 476 US-B 67 99 476, US-B 67 76 053, US-B 67 69 301, US-B 65 77 989, US-B 66 62 120, US-B 65 74 515, US-B 65 35 161, US-B 65 12 358, US-B 64 87 507, US-B 64 80 131, US-B 64 76 522, US-B 63 97 683, US-B 63 52 000, US-B 63 11 136, US-B 62 85 094, US-B 62 69 701, US-B 62 36 322, US-A 61 40 940, US-A 60 14 100, US-A 60 06 609, US-A 59 59 372, US-A 57 96 011, US-A 57 42 225, US-A 57 42 225, US -A 56 87 100, US-A 56 72 975, US-A 56 04 685, US-A 55 35 243, US-A 54 69 748, US-A 54 16 723, US-A 53 63 341, US-A 53 59 881, US-A 52 31 884, US-A 52 07 101, US-A 51 31 279, US-A 50 68 592, US-A 50 65 152, US-A 50 52 230, US-A 49 26 340, US-A 48 50 213, US-A 47 68 384, US-A 47 16 770, US-A 46 56 353, US-A 46 17 607, US-A 45 94 584, US-A 45 74 328, US-A 45 24 610, US-A 44 68 971, US-A 43 17 116, US -A 43 08 754, US-A 38 78 725, EP-A 1158289, EP-A 1147463, EP-A 1058093, EP-A 984 248, EP-A 591 926, EP-A 525 920 or EP-A 415 655, DE-A 44 12 388 or DE-A 39 34 007. extensive and detailed. The field devices shown therein have a power from an external electrical power supply, which provides a supply voltage and one of them driven the field-device electronics by flowing supply current supplies respectively.

p0006[0003] In the event that the field device serves as a measuring device, it further comprises a corresponding physical-electrical or chemical-electrical transducer for detecting the respective process variables. This is mostly used in a wall of the respective leading the medium container or each leading in the course of the medium line, for example, a pipeline and serves at least one primarily sensed process size as closely as possible representative, esp. Electric generating measuring signal , For processing of the measurement signal of the measuring transducer is further to that provided for in the field-device electronics, esp. Also further processing or evaluation of serving at least one measurement signal, operating and evaluating circuit connected. In a variety of such field devices, the measuring transducer is also driven to generate the measuring signal in the operation of an at least intermittently generated by the operating and evaluating circuit driving signal so that it at least indirectly in a form suitable for measurement manner corresponding to the medium, or also on a probe acts virtually directly to the medium to there cause the parameters to be measured corresponding reactions. The drive signal can be controlled in accordance with, for example, with respect to a current, a voltage level and / or a frequency. As examples of such active, ie an electrical drive signal in the medium appropriately converting transducer are in special measuring serving of at least intermittently flowing media flow transducer with at least one driven by the driving signal, magnetic field generating coil or at least one driven by the driving signal ultrasonic transmitter or the measuring and to call / or monitoring of fill levels in a container serving level and / or Grenzstandsaufnehmer such as microwave antennas, Goubau lines, ie a waveguide for acoustic or electromagnetic surface waves, vibrating immersion element or the like.

p0007[0004] To accommodate the field-device electronics further include field devices of the type described an electronics housing, such as proposed in US-A 63 97 683 or WO-A 00/36379, arranged from the field device and with this only can be connected via a flexible cable or the like shown in EP-a 903 651 or EP-a 1,008,836, directly on the transducer or transducer disposed one to separately housing the measuring transducer housing. often then used the electronics housing, as shown for example in EP-A 984 248, US-A 45 94 584, US-A 47 16 770 or US-A 63 52 000 also, some mechanical components of the measuring transducer incorporated with, for example under mechanical action operatively deforming membrane, rod, also the above-mentioned US-B sleeve or tubular Deformation or vibration body, see FIG. For this purpose 63 52 000. field devices of the type described are furthermore usually at a the field-device electronics connected data transmission system and / or connected to each other with corresponding process control computers, where they send the measured value signals eg via (4 mA to 20 mA) current loop and / or via digital data bus and / or from which they operating data and / or receive control commands in a corresponding manner. As data transmission systems serve here, esp. Serial, fieldbus systems such as PROFIBUS-PA, FOUNDATION HELDBUS and the corresponding transmission protocols. By means of the process control computers, the transmitted measured value are further processed and visualized as corresponding measurement results eg on monitors and / or converted into control signals for other than actuators trained field devices, such as solenoid valves, electric motors, etc..

p0008[0005] furthermore, a plurality of field devices of the type described, esp. Also

p0009Field measuring device, electrically designed such that they meet the requirements for intrinsic safety explosion. Accordingly, the field devices with such a low electric power to operate, that the absence of reaching the ignition conditions sparks or arcs electrically can not be triggered. Eigensicherere explosion protection is given, for example, according to European standard EN 50 014 and EN 50 020, when electronic devices are designed such that they comply with the defined therein "intrinsically safe (Ex-i)". ie occurring in the field device electrical currents, voltages and power predetermined current, voltage and power limits According to this type of protection shall not exceed at any time. These three thresholds are chosen so that in case of failure or by a short circuit, the maximum amount of energy released is insufficient to produce an ignitable sparks. Usually, in intrinsically safe field devices must not exceed the electric power 1 W (= W). The voltage can be maintained eg by Zener diodes, the current eg by resistors and the power by appropriate combination of voltage and current limiting components exceed the specified limit.

p0010[0006] In modern field devices also often concerns so-called

p0011Two-wire field devices, ie those field devices, in which the field-device electronics is electrically connected to the external electrical power supply solely via a single pair of electric lines and in which the field-device electronics Also the current measured value on the single pair of electrical leads to an opening provided in the external electrical power supply and / or transfers with these electrically coupled evaluation. The field-device electronics comprises in each case one through which the supply current flow controller for adjusting and / or modulating, esp. Measures, the supply current, an internal operating and evaluating circuit for controlling the field device, and an internal on one divided by the supply voltage input voltage of the field-device Electronics applied, the internal operating and evaluating circuit supplying internal supply circuit with at least one of a variable partial flow of the supply current-carrying voltage regulator that a provides to a predetermined voltage level substantially constant regulated internal useful voltage in the field-device electronics. Examples of such two-wire field devices, esp. Two-wire measuring devices or two-wire actuators, can inter alia WO-A 03/048874, WO 02/45045, WO-A 02/103327, WO-A 00/48157, WO-A 00/26739, WO-A 94/20940, US-B 67 99 476, US-B 65 77 989, US-B 66 62 120, US-B 65 74 515, US- B 65 35 161, US-B 65 12 358, US-B 64 80 131, US-B 63 11 136, US-B 62 85 094, US-B 62 69 701, US-A 61 40 940, US-A 60 14 100, US-A 59 59 372, US-A 57 42 225, US-A 56 72 975, US-A 55 35 243, US-A 54 16 723 , US-A 52 07 101, US-A 50 68 592, US-A 50 65 152, US-A 49 26 340, US-A 46 56 353, US-A 43 17 116 EP-A 1147841, EP-A 1058093, EP-A 591 926, EP-A 525 920, EP-A 415 655, DE-A 44 12 388 or DE-A 39 34 are taken 007th Historically such two-wire field devices are primarily designed so that one on one between 4 mA and 20 mA (= milliamps) value lying set instantaneous current strength of the in the constructed as a current loop single pair line currently flowing supply current at the same time the measured value currently generated by the field device or the set currently being transmitted to the field device represents. Consequently, there is a particular problem of such a two-wire field devices to the extent that the of the field-device electronics at least nominally actionable or reacted electric power - in brief "available power" - during operation in practically unpredictable manner can vary over a wide range. Taking this into account are modern two-conductor field devices (2L field devices), esp. Modern two-wire measuring devices (2L-measuring devices) with (4 mA to 20 mA) current loop, therefore, usually designed so that their and in the evaluation by means of a operating circuit provided for the microcomputer implemented device functions can be changed, and thus the already low power-converting mostly operating and evaluating circuit can be adapted to the currently available power. [0008] A suitable adaptation of the field-device electronics to the available power can, for example, as well as in US-B 67 99 476, US-B 65 12 358 or US-A 54 16 723 proposed by matching the currently in the field device converted power can be achieved at the currently available power, and in such a way that individual functional units of the operating and evaluating circuit operated with appropriately variable clock rates or, depending on the level of the currently available power, even temporarily be off (standby or sleep mode ). When designed as a two-wire measuring device field devices with active measuring transducer, the currently implemented in the field device electrical power, such as, inter alia, in US-B 67 99 476, US-A 60 14 100 or WO-A shown 02/103327, also by adjusting and the currently implemented in the transducer electric power are adapted to the currently available power, for example by clocking the optionally buffered driver signal along with a correspondingly adaptable excess rate at which the drive signal is clocked, and / or by decreasing a maximum current and / or a maximum voltage level of the driving signal.

p0012[0009] has, however, when configured as a two-wire instrument field devices a change of equipment functionality usually also means that in operation an accuracy with which determines the operating and evaluating the measured value, and / or frequency with which the operating and evaluating, for example, updates the measured value, a function of the power currently available is subject to changes. Also buffering temporarily existing surplus power can remedy this disadvantage of two-wire measuring devices with (4 mA to 20 mA) current loop only conditionally. On one hand, can be stored in any case only a very limited extent internally in the field device electronics because of the usually often equally required for such two-wire measuring intrinsic safety explosion possibly present excess electrical energy. On the other hand, the current supply current and so far also the possibly present excess energy depends only on the current measured value, so that therefore in permanently very low, in time but widely fluctuating measured a correspondingly provided energy buffer may be completely discharged over a longer period entirely. In addition, for the implementation of such a complex power management in the field device a very extensive and far too much of circuitry and energy-consuming power measurement is required, see. See also the WO 00/26739, US-B 67 99 476, US-B 65 12 358 or the EP-A 1,174,841.

p0013[0010] Apart from that has also been found in field devices of the type described with the guiding and measuring of serving at least intermittently flowing media measurement pickup that the adaptive clocking drive signal and / or is any component of the operating and evaluating only conditionally suitable. This is especially true when using a measuring transducer of vibration-type, such as those in the above-mentioned US-B 67 99 476, US-B 66 91 583, US-A 60 06 609, US-A 57 96 011 US Pat 56 87 100, US-A 53 59 881, US-A 47 68 384, US-A 45 24 610 or WO-A 02/103327 are described. The field devices shown there are the measuring parameters in pipelines flowing media, especially the mass flow rate, density or viscosity. For this purpose, the corresponding transducer in each case at least one operating vibrating, the conveying of the medium serving measuring tube, an electrode electrically connected to the field device electronics exciter arrangement with an on the measuring tube acts mechanically vibration exciter for driving the flow tube, and a sensor arrangement measuring tube oscillations comprises locally representing measurement signals by means of at least one arranged on the measuring tube vibration sensor generates. Both the vibration exciter and the vibration sensor is preferred in this case the electro-dynamic type, so each case by means of a magnetic coil and a with this interacting with a magnetic plunger formed.

p0014[0011] Due to the highly accurate amplitude necessary for the operation of such a measuring transducer - and frequency control of the drive signal for the exciter assembly for a time is a high-resolution scanning of the measuring tube oscillations indispensable. Similarly, is also self-updating comparatively often made to with flowing media measurements of the output measurement. For another, a generally very high mechanical time constant of the vibration system formed by the transducer to that of the same for any accelerations, esp. During unsteady transients, a high drive power is required and / or or comparatively long settling times must be estimated. Proceeding this, investigations have, however, also been found that is able to hardly cause a significant improvement in dependent on the amplitude of the measuring tube oscillations signal-to-noise ratio because of the usually limited storage for electric power, a buffering excess energy in the field device. In that regard, including a temporary and partial shutdown of the operating and evaluating circuit is for two-wire measuring devices with an active transducer of the aforementioned type, esp. For two-wire measuring devices with the guiding flowing media serving vibratory transducer, little suited.

p0015[0012] Another way to improve the performance of field devices of the type described, esp. The two-wire measuring instruments, is as much as possible thereof for the implementation of the device functions effectively to use at least at a minimum available power, so a corresponding efficiency to optimize the field device at least in the region of small power available, the corresponding supply circuits for the internal supply of the field device electronics are, for example, in US-B 65 77 989 or US-A 61 40 940 discussed in detail. In particular, it proposes solutions aim to optimize the internal factually possible electric power. For each a set and maintain the above-mentioned internal input voltage of the field-device electronics on a predetermined, possibly also conformable, voltage level serving input voltage controller is provided with an introduction to the field-device electronics acting stress Steep in the field-device electronics, the function of presently available power and an instantaneously actually needed power from a power supply from the branched, variable partial flow is at least intermittently flowed through. However, a disadvantage of the aforementioned field-device electronics is that all internal consumers are practically supplied by one and the same internal useful voltage and Any other collapse this single useful voltage, for example due to an excessively low supply current, no longer allows normal operation of the field device or even suddenly to may cause a temporary loss of total-field-device electronics.

p0016[0013] is the basis of the above the example of conventional 2L-measuring devices discussed disadvantages of the prior art, an object of the invention to provide a suitable for a field device of the type described field-device electronics, which enables the evaluation and operating circuit esp. a microprocessor provided therein, at least permanently keep in normal operation of the field device in transition and thereby at least selected ones of the functional units, esp. the microprocessor provided to always provide a sufficient degree of electrical energy.

p0017[0014] For achieving the object of the invention in a fed from an external electrical power supply field-device electronics for a field device, wherein the external electrical power supply a, esp. Uni-polar, provides power supply and one of them driven, esp. Uni-polar and / or binary, variable supply power supplies, includes which field-device electronics:

p0018[0015] - a through which the supply current flow controller for adjusting and / or modulating, especially clocking, the supply current.

p0019[0016] - an internal operating and evaluating circuit for controlling the field device, and

p0020[0017] - a voltage applied to a divided from the supply voltage internal input voltage of the field-device electronics, the internal operating and evaluating circuit supplying internal supply circuit

p0021[0018] - with an at least temporarily by an, especially variable, first partial flow of the supply current-carrying first voltage regulator, on the one one. predeterminable first voltage level substantially constant controlled first internal useful voltage in the field-device electronics provides,

p0022[0019] -. With an at least temporarily by an, especially variable, second

p0023Partial flow of the supply current d urchflossenen second voltage regulator which provides a variable over a predetermined voltage range second internal useful voltage in the field-device electronics, and

p0024[0020] - with an at least temporarily by an, especially variable, third partial flow of the supply current-carrying voltage Steep for setting and maintaining the internal input voltage of the field-device electronics on a predetermined, in particular variable in operation, voltage level..

p0025[0021] -. Wherein the operating and evaluating circuit at least temporarily, from both a driven by the first useful voltage, especially variable, first useful current as well as a driven by the second useful voltage, especially variable, second useful current is flowing through it..

p0026the invention [0022] Further, in a field device which comprises the aforementioned field device electronics. In a first variant of the field device of the invention serves this to the measuring and / or monitoring at least one predetermined physical and / or chemical parameter, esp. A flow rate, a density, a viscosity, a level, a pressure, a temperature, a pH or the like, a, esp. in a pipeline and / or a container-managed, medium, and further includes the field device for a with the field-device electronics electrically coupled physical-electrical transducer which is responsive to changes of the at least one parameter and at least temporarily at least with the parameter measurement signal corresponding, esp. a variable signal voltage and / or a variable signal current, emits. In a second variant of the field device of the invention this adjustment is used at least one predetermined physical and / or chemical parameter, esp. A flow rate, a density, a viscosity, a level, a pressure, a temperature, a pH value or the like, a, esp. in a pipeline and / or a container out, and the field device includes for further one with the field-device electronics electrically coupled electrically-physical actuator which, especially on changes of at least one control signal applied. a variable signal voltage and / or a variable signal current , reacts with a the adjusted parameter influencing adjustment of the actuator.

p0027[0023] In a first embodiment of the invention, the internal input voltage of the field-device electronics and / or the second useful voltage of the field-device electronics as a function of an instantaneous voltage level of a divided by the supply voltage to the field-device electronics dropping from the input terminal belt tension regulated. According to a development of this embodiment of the invention, the internal input voltage of the field-device electronics by means of the voltage on a predetermined steller, esp. In the variable operation, held voltage level that is lower than the terminal voltage. The voltage level at which the internal input voltage is held by means of the voltage controller, may during operation, especially, step-wise or essentially continuously vary.

p0028[0024] In a second embodiment of the invention, the second useful function of an instantaneous voltage level of the internal input voltage of the field-device electronics and / or regulated as a function of an instantaneous voltage level of a divided by the supply voltage to the field-device electronics dropping from the input terminal voltage ,

p0029[0025] In a third embodiment of the invention, the second useful function of an instantaneous current is at least regulated of the three streams. According to a development of this embodiment of the invention provides that the second useful voltage is controlled depending on the instantaneous current of the third part of current. In another further development of this embodiment of the invention is further provided that the second useful voltage is controlled depending on the instantaneous current of the second substream and an instantaneous voltage level of the internal input voltage of the field-device electronics.

p0030[0026] In a fourth embodiment the invention provides the feeding external power supply voltage variable, esp. Fluctuating, voltage level ready.

p0031[0027] In a fifth embodiment of the invention, the power supplied by the external power supply voltage supply drives a supply current variable, esp. In substantially advance not determinable manner fluctuating, amperage.

p0032[0028] In a sixth embodiment of the invention is erte- in the operating and Sel circuit provided a the temporarily storing electric energy serving memory circuit.

p0033[0029] In a seventh embodiment of the invention, the voltage Steep primarily the dissipation of electrical energy and the removal of this heat energy arising serving components, esp. A semiconductor element or the like, on.

p0034[0030] In an eighth embodiment of the invention, at least one microprocessor and / or a digital signal processor is provided in the operating and evaluating, wherein the first useful voltage, or one of them derived secondary voltage at least partially serves as operating voltage. [0031] In a ninth embodiment of the invention, an amplifier is provided in the operating and evaluating at least, in which at least one of the two useful voltage, or one of them derived secondary voltage at least partially serves as operating voltage.

p0035[0032] In a tenth embodiment of the invention, at least one A / D converter is provided in the operating and evaluating, wherein the first useful voltage, or one of them derived secondary voltage at least partially serves as operating voltage.

p0036[0033] In an eleventh embodiment of the invention, a D / A converter is provided in the operating and evaluating at least, in which at least one of the two useful voltage, or one of them derived secondary voltage at least partially serves as operating voltage.

p0037[0034] In a twelfth embodiment of the invention, means for comparing sloping in the field-device electronics electrical voltages and / or current flowing in the field-device electronics electric currents are provided with reference values ​​in the operating and evaluating. According to a development of this embodiment of the invention, the operating and evaluating circuit generates at least then an insufficient supply of the field device electronics signaling alarm signal when the operating and evaluating the reduction of an for the second useful voltage predetermined minimum useful voltage by the second useful voltage and below a predetermined for the third current component part minimal current limit value detected by the third current component. After another development of the invention, the field device electronics further includes at least one comparator for comparing an inferred from the third partial stream of the supply current sense voltage with an associated reference voltage and / or a comparator which compares the second useful voltage with at least one associated reference voltage.

p0038[0035] In a thirteenth embodiment of the invention, this further comprises the

p0039Producing substantially current-proportional sense voltage serving sense resistors.

p0040[0036] In a fourteenth embodiment of the invention, this further comprises a

p0041Measuring and control unit for registering and adjusting voltages dropping in the field-device electronics tensions, esp. The second useful voltage, and / or in the field-device electronics flowing streams, esp. The second and / or third partial flow. According to a development of this embodiment of the invention the measuring and control unit, the voltage Steep controls so that the third part of current flows when the second useful voltage with at least one associated reference voltage comparator comparative exceeding a predetermined for the second useful voltage maximum useful voltage limit by the second useful signal. According to another further development of this embodiment of the invention, the measuring and control unit based on the input voltage and / or the terminal voltage of an existing between the input voltage and the terminal voltage difference voltage to a predetermined voltage level.

p0042[0037] In a fifteenth embodiment of the invention, the field-device electronics is electrically connected to the external electrical power supply solely via a single pair of electric lines.

p0043[0038] In a first embodiment of the field device of the invention that communicates at least temporarily with a remote from field device external control and control unit via a data transmission system, wherein it further comprises a controlling communication circuit is the communication in the field-device electronics via data transmission system is provided. According to a development of this embodiment of the invention, the first useful voltage, or one of them partitioned secondary voltage is at least in part as an operating voltage for the communication circuit.

p0044[0039] In a second embodiment of the field device according to the first variant, the operating and evaluating the field-device electronics by means of at least one measurement signal measurement produces a said at least one to be measured and / or currently being monitored parameters, esp. Digital, representing at least temporarily , According to a development of this embodiment of the invention, the current regulator to supply power on taking account of the at least one to be measured and / or monitored parameters instantaneously representing the measured value. In another further development of this embodiment of the invention, the supply current is a variable DC and is the current controller adapted at least temporarily to modulate the measured amplitude of the supply current to.

p0045[0040] In a third embodiment of the field device according to the first variation of the supply current is at least temporarily, is a clocked current and wherein the current regulator adapted to clock the supply current.

p0046[0041] In a fourth embodiment of the field device according to the first variant, the operating and evaluating circuit includes at least one driver circuit for the transducer, wherein the second useful voltage, or one of them derived secondary voltage at least partially serves as operating voltage. According to a development of this embodiment of the invention, the driver circuit at least OpAmps on. In another further development of this embodiment of the invention, the driver circuit at least one D / A converter and / or at least one signal generator for generating the driving signal. According to a next wheat terbildung this embodiment of the invention, the measuring transducer is a fed from the driver circuit, esp. variable, electrical impedance, esp. a solenoid of variable inductance and / or a measuring capacitor of variable capacitance. It is also planned that a to be measured and / or changes the electrical impedance of the transducer as a function of at least the monitored parameters. Furthermore it is provided that one over the changing electrical impedance signal voltage falling and / or a current flowing through the electrical impedance varying signal current is used as a measurement signal.

p0047[0042] In a fifth embodiment of the field device according to the first variant, the operating and evaluating at least one A / D converter for the at least one transducer signal on, wherein the first useful voltage, or one of them derived secondary voltage at least partially serves as operating voltage. According to a development of this embodiment of the invention, the operating and evaluating at least connected one with the A / D converter, esp. By a microprocessor and / or a signal processor formed, microcomputer for generating the measured value, wherein the first useful voltage, at least partially serves as an operating voltage of the microcomputer.

p0048[0043] In a sixth embodiment of the field device according to the first variant of the measurement pickup includes at least one inserted into the course of a pipeline, esp. At least temporarily vibrating in operation, measuring tube for guiding the medium. According to a development of this embodiment of the invention the magnetic field is at least one transducer coil for generating a, esp. Variable, arranged. According to one embodiment of the invention, the magnetic coil is at least temporarily generating the magnetic field during operation of the measurement pickup of an, especially. Bipolar and / or variable in a current, flowing through exciting current derived from the second useful voltage, or one of them secondary voltage is driven. According to another embodiment of the invention, the magnetic coil is via magnetic field with a solenoid plunger interacts, and said magnetic coil and plunger relative to each other are movable. According to a further embodiment of this refinement of the invention, which vibrates at least one measuring tube of the measuring transducer, driven by a formed by the magnetic field coil and the solenoid plunger electromechanical, esp. Electrodynamic, exciter mechanism, the operation of the transducer at least temporarily.

p0049[0044] According to another development includes the field device according to the first variant of the measurement pickup two in the course of the pipe used, during operation, at least temporarily vibrating measuring tubes for guiding the medium.

p0050[0045] is a seventh embodiment of the field device according to the first variant the measuring transducer detecting at least one parameter of a medium derivative container, esp. a liquid level, and at least the measuring transducer for a projecting into a lumen of the container or at least communicates with the lumen probe, esp. a microwave antenna, a Gouboun- line, a vibrating immersion element or the like.

p0051[0046] In an eighth embodiment of the field device according to the first variant, the field-device electronics is electrically connected to the external electrical power supply solely via a single pair of electric lines and transmits the field-device electronics to at least temporarily generated, the at least one to be measured and / or to be monitored parameter currently, esp. digital, representing measured on the single pair of electrical leads to an opening provided in the external electrical power supply and / or electrically coupled to the evaluation circuit. According to a development of this embodiment of the invention represents a momentary, esp. In a set between 4 mA and 20 mA value lying, amperage of the supply current to the measured value currently produced.

p0052[0047] A basic idea of ​​the invention is provided in the field-device electronics consumers - apart from the supply circuit itself - on the one hand, at least in a first group of electrical circuits or consumers of higher priority and in a second group of electrical circuits or consumers of lower priority to divide, and on the other hand, the supply circuit be designed so that at least the power or energy demand of the first group of electric circuits is always covered in normal operation of the field device. Moreover, such circuits or components which are mainly used to store electrical energy internally in the field device and / or to have electrical energy from the field device out dissipate, be assigned to a third group of electrical consumers that only when an adequate supply of the first and second group electrical load current flowing through it and is therefore supplied with electric energy.

p0053[0048] The first group of electric circuits of higher priority are advantageous in production systems including at least one provided in the field-device electronics microprocessor and the communication with any parent command and control units serving communication circuits assigned. This has the advantage that the field device on the one hand permanently in function and on the other hand, at least also can be permanently kept on-line. Further, in the event that it is the field device is a measuring device, and the detection and treatment of at least one measurement signal measuring channel serving mainly the first group of electric circuits are assigned, while possibly present, mainly operating the electrically-physical measurement pickup serving excitation channels are implemented as electrical circuits of lower priority. This has permanently when using the field-device electronics of the invention in a measuring apparatus with a vibratory transducer in particular the advantage that virtually all, extending from the vibration sensors to the microprocessor measuring channel is operated with the first useful voltage substantially constant regulated and therefore in normal operation the electrical power required can be supplied. This has the advantage that as far as the measuring tube oscillations operationally generated can be processed always sampled equally high frequency and also highly resolved. Further, even if the excitation channel is operated partly or solely due to the variable second useful voltage, the measuring tube in normal operation - albeit with possibly fluctuating oscillation amplitude - are virtually completely, ie permanently excited. etc. The invention is based on the realization that neither the temporary shutdown of the microprocessor, nor the lückende operation can cause, for example, the excitation channel substantial improvements in the energy balance of the field device. Rather, it depends on possible permanent and ample supply on the one hand the vital for the operation of the field device and, if the communication components with energy and on the other hand, if necessary, rather less essential components optionally provide unterzu- or disable. Furthermore, it has been shown that - especially in continuously or at least quasi-continuously measuring field devices, such as Coriolis mass flow measuring devices, -. Can be far more rewarding, the available electrical energy primarily in the at least one microprocessor, especially the measured value processing and analysis to invest, to operate as for example in the exciter mechanism of the sensor system, and in accordance with the rest of the available energy. Although in this way may not always an optimum signal can be achieved to-noise ratio for the delivered from the measuring sensor measurement signal that any existing deficit of quality of the measurement signal can, however, be offset by the measured value processing and analysis readily that the after as realized before operating efficiently microprocessor. Another advantage of the invention is that the field device can comply with the rules of the various explosion protection classes without further due to the low power required for its operation. This field device is particularly suitable for use in such hazardous environments where only devices are allowed by intrinsic safety. Furthermore, the field device can be in this case designed such that it can work with any of the conventional fieldbuses. This may on the one hand by direct connection to the fieldbus, z. B. according to the FTELDBUS protocol, done (FIELDBUS is a one- worn brand of HELDBUS FOUNDATION). On the other hand, the cooperation by means of a bus coupler, z. B. in accordance with the so-called HART protocol, done indirectly (HART is a registered trademark of the HART User Group).

p0054[0050] The invention will now be explained in more detail with reference to embodiments and the drawing figures. Functionally identical parts are provided in the individual figures with the same reference numbers, however, are only repeated in subsequent figures if it makes sense.

p0055[0051] FIG. 1 shows in perspective a side view of a field device as well as electrically connected with this via a pair of electrical lines external power supply,

p0056[0052] FIG. 2 partially in section showing an embodiment of a suitable for the field device of FIG. 1 measuring transducer of vibration-type perspective in a first side view,

p0057[0053] FIG. 3 shows the transducer of Fig. 2 in perspective in a second side elevation,

p0058[0054] FIG. 4 shows an embodiment of an electromechanical driver assembly for the sensor of Fig. 2,

p0059[0055] FIG. 5 shows the manner of a block diagram a for use in a field device, esp. A two-wire field devices, suitable field-device electronics,

p0060[0056] FIGS. 6 to 8 show partly in block-diagram circuit diagrams of embodiments of a for use in a field device of FIG. 1 with a vibratory transducer shown in FIGS. 2 to 4 suitable exciter circuit,

p0061[0057] FIGS. 9 to 12 show circuit diagrams of exemplary embodiments of the exciter circuits according to FIGS. 6 to 8 suitable amplifiers,

p0062[0058] FIGS. 1, an embodiment of a suitable for use in industrial measurement and automation technology field device with a field-device electronics 20 is shown, which is fed by an external electric power supply 70. In operation, the external electric power supply 70 a esp. Uni-polar, supply voltage U ready and supplies the external electric power supply 70, consequently a correspondingly driven by the supply voltage U variable, esp. Binary, supply current I. For this is the field-device electronics electrically operatively connected to the external electrical power supply 70 via at least a pair of electrical lines 2L. Due to the external power supply between 70 and input of the field-device electronics 20 naturally occurring voltage drops the supply voltage U in this way is, however, yet to the beginning of the field-device electronics actually other lying terminal voltage U is reduced.

p0063[0059] According to one embodiment of the invention, the field device electronics is designed and dimensioned such that a maximum of converted electric power is less than or at most equal to 1 W. According to another embodiment of the invention, the field-device electronics is designed and dimensioned so that the field device is applicable intrinsically safe that the, for example, in the European standards EN 50 014 and EN 50 020, laid down in the sense of explosion protection requirements an intrinsic explosion safety (Ex-i) is sufficient.

p0064[0060] The field device is used in accordance with another embodiment of the invention to at least one predetermined physical and / or chemical parameters such as a flow rate, a density, a viscosity, a level, a pressure, a temperature, pH or the like , one in a pipeline and / or a container guided medium, especially, to measure a gas and / or liquid, and / or monitor and repeated to provide these parameters according representing the measured value. For the field device further comprises a with the field-device electronics electrically coupled physical-electrical transducer which is responsive to changes of the at least one parameter and at least temporarily at least one with the parameter measurement signal corresponding, esp. A variable signal voltage and / or a variable signal current outputs, , Alternatively or in addition thereto, a be provided with the field-device electronics electrically coupled electrically-physical actuator in the field device, which changes at least one applied control signal, esp. A variable signal voltage and / or a variable signal current, influencing with the adjustable parameter adjustment the actuator responding, or in other words, the field device can for example also be designed so that it is used to adjust at least one of such physical and / or chemical parameter of the medium. To control the field device, esp. Also for driving the aforementioned transducer or for driving the mentioned actuator, an internal operating and evaluating circuit 50 is provided in the field-device electronics further. In the event that it is the field device is a measuring the at least one predetermined physical and / or chemical parameters serving instrument, it is further provided that the operating and evaluating circuit 50 to at least one measured value or a plurality of corresponding measured values determined for the parameter.

p0065. [0061] The field device shown in Figure 1 is an in-line measuring device, which is used in particular to parameters, such as a mass flow rate, a density and / or viscosity, of a - not shown here - pipeline flowing medium, especially for detecting a gas and / or a liquid, and in this one. Parameters instantaneously representing the measured value X mapping. Accordingly, may be the field device such as a Coriolis mass flowmeter, a density meter, or a viscosity measuring device. To generate the least one measurement signal, the field device shown here includes an accommodated within a corresponding measurement pickup housing 100, transducer 10 of vibration type and a displayed at an electronics housing 200, in which the field-device electronics to the transducer 10 suitably electrically connected 20 is housed.

p0066[0062] FIGS. 2 to 4, an embodiment of such a transducer is shown, the structure and operation of the rest as well as in the US-A 60 06 609 described in detail. However, it is already noted at this point that, although it is the case for this in the embodiment of the field device is an in-line measuring device is a vibratory transducer, the invention of course also in other field devices, for example those in-line measuring devices with magnetic-inductive measuring transducer or with acoustic transducer, can be implemented. Similarly, the present invention can also be used in field devices that are used measuring parameters, as determined derivative forming containers in connection with media, such as a level and / or a limit level. Such field devices are usually realized by means of such measuring transducers, a protruding into a lumen of the container or at least communicating with the lumen probe, for example, a microwave antenna, a Goubau line, a vibrating immersion element or the like at least.

p0067[0063] For conveying the medium to be measured includes the transducer 10 of the embodiment of FIGS. 2 to 4, at least one having an inlet end 11 and an outlet end 12 exhibiting measuring tube 13 of predeterminable, in operation elastically deformable Meßrohrlumen 13A and a predeterminable nominal diameter. Elastic deformation of the measuring tube lumen 13A here means that for generating the aforementioned above medium internal and therefore the medium reaction forces describing a three-dimensional shape and / or a spatial position of the measuring tube lumen 13A within an elastic range of the measuring tube 13 in predeterminable manner cyclically, esp. Periodically, is changed . see for example, US-A 48 01 897, US-A 5 648 616, US-A 57 96 011 or the US-A 60 06 609. If necessary, the measuring tube, such as in EP-A 1 260 798 shown, for example, be also bent. In addition, for example, is also possible, instead of a single measuring tube, two curved or straight measuring tubes to use. Other suitable embodiments of such vibratory transducer are described eg in US-B 67 11 958, US-B 66 91 583, US-B 66 66 098 US Pat 53 01 557, US-A 53 57 811 , US-A 55 57 973, US-A 56 02 345, US-A 5648 616 or US-A 57 96 011 described in detail. As the material for the in Figs. 3 and 4 straight measuring tube 13, for example, titanium alloys are particularly suitable. Instead of titanium alloys but may also be of such other, esp. For curved flow tubes commonly used materials such as stainless steel, tantalum or zirconium etc. can be used.

p0068[0064] The measuring tube 13, the inlet and outlet ends with the to-the medium in the usual way or discharging piping communicates, is in a rigid, esp. In bending and torsion-resistant, and the transducer housing 100 covered, supporting frame 14 oscillatably clamped. The support frame 14 is fixed by means of an outlet plate 223 on the measuring tube 13 on the inlet side by means of an inlet plate 213 and outlet, the latter two are pierced each of respective extension pieces 131, 132 of the measuring tube. 13 Furthermore, the support frame 14, a first side plate 24 and a second side plate 34 on which two side plates 24, 34 are respectively so fixed to the inlet plate 213 and to the outlet plate 223, that it virtually parallel to the measuring tube 13 and spaced therefrom and from each other, are arranged. see Fig. 3. Thus, mutually facing side surfaces of the two side plates 24, 34 also in parallel. A longitudinal rod 25 is fixed to the side plates 24, 34, spaced from the measuring tube 13, fixed to the balancing mass 13 serves as the vibrations of the measuring tube. The longitudinal bar 25 extends, as shown in Figure 4, practically parallel to the entire oscillatable length of the measuring tube. 13; However, this is not mandatory, the longitudinal bar 25 may, of course, if necessary, be made shorter. The support frame 14 with the two side plates 24, 34, the inlet plate 213, the outlet plate 223 and the longitudinal rod 25 thus has a longitudinal centroidal axis, leading to an inlet end 11 and the outlet 12 connecting virtual measuring tube center axis 13B runs practically parallel. In Figs. 3 and 4 is indicated by the heads of the screws drawn that the mentioned fixing the side plates 24, 34 can be carried out on the inlet plate 213 at the outlet plate 223 and on the longitudinal bar 25 by screwing; but there may be other suitable and known to the expert mounting styles are applied. In the event that the measuring transducer 10 is releasably mounted to the pipeline, the measuring tube 13, a first flange, a second flange on the inlet side 119 and outlet 120 are formed, see Fig. 1. instead of the flanges 19, 20 may, for example, but also other pipe fittings for the detachable connection with the pipeline to be formed, such as the 3 indicated in FIG. triclamp so called connections. If necessary, the measuring tube 13 but also directly with the pipeline, eg by means of welding or brazing, etc. are connected or be

p0069[0065] For producing the mentioned Reaktionskäfte in the medium, the measuring tube 13 in operation of the measuring transducer 10, driven by a will coupled with the measuring tube electro-mechanical excitation device 16, at a predetermined oscillation frequency, esp. a natural resonance frequency, left and thus elastically deformed in predeterminable manner vibrate the so-called wanted mode. As already mentioned, this resonance frequency is also dependent on the instantaneous density of the fluid. In the illustrated embodiment, the vibrating measuring tube 13, as with such measuring transducers of vibration type is common, spatially from a static rest position, especially laterally, deflected. the same applies in practice for such measurement pickups, which carry one or more curved measuring tubes cantilever vibrations about a corresponding, the respective inlet and outlet ends virtually connecting, imaginary longitudinal axis, or also for those transducer in which one or more straight measuring tubes only planar flexural vibrations about their measuring tube run. In another case that performs peristaltic radial vibrations as the measuring transducer 10, such as described in the aforementioned WO-A 95/16 897, so that the cross-section of the vibrating measuring tube is symmetrically deformed in the customary manner, the measuring tube remains in its static rest position. The exciter arrangement 16 serves to generate a force acting on the measuring tube 13 exciting force F exe exe while converting an input from the operating and evaluating 50 inform an electric drive signal electrical excitation power P. The excitation power P is when excited at a natural resonance nanzfrequnz practically only to compensate for the above mechanical and fluid internal friction the vibration system confiscated power component. To achieve the highest possible efficiency, the excitation power P is therefore exe adjusted as closely as possible so that essentially, be maintained the oscillations of the measuring tube 13 in the desired useful mode, for example, a fundamental resonance frequency. For the purpose of transmitting the excitation force F on the measuring tube exe

p007013, the exciter arrangement 16, as shown in Fig. 5, a rigid, electromagnetically and / or electro-dynamically driven lever arrangement 15 with the measuring tube 13 flexural strength fixed cantilever 154 and a yoke 163. The yoke 163 is also fixed to bending at a location spaced from the measuring tube 13 the end of the boom 154, and in such a way that it is arranged above the measuring tube 13 and transversely to it. When cantilever 154, for example, can be used a metallic plate, which receives the measuring tube 13 in a bore. For further suitable implementations of lever arrangement 15, reference is made at this point to the already mentioned US-A 60 06 609th The lever arrangement 15 is T-shaped and is arranged see. FIG. 5 in that it. Approximately in the middle between inlet and outlet ends 11, 12 acts on the measuring tube 13, whereby this centrally experiences its greatest lateral deflection during operation To drive the lever arrangement 15, excitation assembly 16 of FIG. 5 includes a first solenoid coil 26 and an associated first permanently magnetic armature 27 and a second magnet coil 36 and an associated second permanent-magnetic armature 37. The two electrically preferably in series-connected coils 26, 36 are on both sides of the measuring tube 13 below the yoke 163 on the support frame 14, esp. releasably, fixed so that they with their each associated armature 27 or 37 in operation interact. The two solenoids 26, 36, can also be, if necessary, of course, each connected in parallel. As shown in FIGS. 3 and 5, the two anchors 27, 37 in such a manner spaced from each other fixed to the yoke 163 that, in operation of the transducer 10 of the armature 27, practically by a magnetic field of the magnetic coil 26 and the armature 37 practically by a magnetic field of the solenoid 36 passes through, and due to a corresponding electro-dynamic and / or electromagnetic force effects, esp. in the respectively associated solenoid immersion, is moved. The acting by means of the magnetic fields of the magnetic coils 26, 36 generated movements, esp. As well as diving anchor, 27, 37 are transferred from the yoke 163 and the boom 154 on the measuring tube. 13 These movements of the armature 27, 37 relative to the respective associated magnet coil are formed so that the yoke 163 is alternately deflected toward the side plate 24 or in the direction of the side plate 34 from its rest position. A corresponding to the already mentioned measuring tube central axis 13B parallel axis of rotation of the lever arrangement 15 may for example pass through the boom 154th The serving as carrier element for the exciter mechanism 16 supporting frame 14 further comprises the side plates 24, 34, esp. Releasably connected holder 29 for holding the magnetic coils 26, 36 and possibly individual components of a specified below magnetic brake assembly 217. In the transducer 10 of the embodiment cause the lateral excursions of the inlet end 11 and outlet end 12 is firmly clamped, the vibrating measuring tube 13 at the same time, an elastic deformation of its measuring tube lumen 13 a, which is virtually formed along the entire length of the measuring tube thirteenth Further, due to a force acting on it over the lever arrangement 15, the torque is at least partially enforced at the same time the lateral displacements rotation about the flow tube center axis 13B in the measuring tube 13, so that the measuring tube 13 virtually in one serving as the wanted mode mixed Biegesc oscillates hwingungs-torsional mode. The twisting of the measuring tube 13 may be formed such that a lateral deflection of the measuring tube spaced from the 13 end of the boom 154, either the same or opposite direction is the lateral deflection of the measuring tube. 13 The measuring tube 13 can thus torsional sion mode or run in a corresponding counter to the case the second flexural-torsional in the same-directed case corresponding first bending-gate. Then the transducer 10 in accordance with the Embodiment, the natural fundamental resonance frequency of the second bending vibrational-torsional mode of eg 900 Hz nearly twice as high as that of the first bending-torsional mode. In the event that the measuring tube 13 operatively vibrations only to perform in the second flexural and torsional mode, a based on the eddy current principle magnetic brake assembly 217 is integrated into the exciter mechanism 16 that serves to stabilize the position of said rotational axis. By means of the magnetic brake assembly 217 can thus be ensured that the measuring tube 13 always oscillates in the second flexural and torsional mode and therefore any external interference is not a spontaneous change to another, especially on the measuring tube 13. Not lead in the first, flexural-torsional. Details of such a magnetic brake assembly are described in detail in US-A 60 06 609th

p0071[0068] For vibrating the measuring tube 13, the exciter arrangement 16 is in Betreib means of a likewise oscillating excitation current i exe, esp. Of adjustable

p0072Amplitude and adjustable excitation frequency f, so fed that the magnetic coils 26, 36 in the operation of this are flowed through and for moving the armature 27, 37 the required magnetic fields are generated in a corresponding manner. The excitation current i, as shown schematically in Fig. 2, provided by an in exe the field-device electronics 20 also provided for the driver unit 50B, and may be for example a harmonic AC. The excitation frequency f of the excitation exc gerst roms i is selected when using a measuring sensor according to the embodiment shown in FIGS. 2 to 4 advantageously so or it adjusts itself so that the laterally oscillating measuring tube 13 solely possible in the second flexural and torsional mode swings.

p0073[0069] It should here be noted that although in the embodiment shown here, the field-device electronics 20 only one fed by the driver unit 50B variable inductive impedance - here a solenoid of variable inductor - which the driver unit 50B can also be adapted to other electric encourage impedances, for example, a measuring capacitor of variable capacitance, or the like. In the case of a capacitive pressure sensor as a transducer at its electrical impedance would then change operation in dependence on at least to be measured and / or to be monitored parameter, known to one over the changing electrical impedance signal voltage falling and / or by changing to electrical impedance signal current flowing serves as the measurement signal.

p0074[0070] For detecting the deformation of the measuring tube 13, transducer 10 further includes a sensor arrangement, which, as shown in Fig. 2, 3, by means of at least one of vibrations of the measuring tube 13 responsive the first sensor element 17 a these repre- sentierendes and as a measurement signal generated s first oscillation measurement. The sensor element 17 may for example be formed by means of a permanently magnetic armature, which is fixed on the measuring tube 13 and interacts with a content Erten from the supporting frame 14 solenoid. As the sensor element 17 are suitable particularly those that detect, based on the electrodynamic principle, a velocity of the deflections of the measuring tube thirteenth However, also acceleration measuring, electrodynamic or even displacement measuring resistive or optical sensors. Of course, other known in the art and for the detection of such vibrations suitable sensors, such as strains of the measuring tube 13 detected sensors may be used. The sensor assembly further comprises a, esp. For the first sensor element 17 identical, second sensor element 18, by means of which they 13 representative and thus provides a also vibrations of the measuring tube as a second measurement signal s serving second oscillation measurement. The two sensor elements 17, 18 are spaced apart at the transducer along the measuring tube 13 shown in the exemplary embodiment, esp. In an equal distance from the center of the measuring tube 13, so arranged that by means of the sensor arrangement 17, 18 inlet side as well as outlet-side vibration of the measuring tube 13 are detected locally and displayed in the corresponding oscillation measurement.

p0075[0071] FIG. 5 shows an embodiment of a device suitable for the field device of Fig. 1 to 4 field device electronics 20 is further schematically the manner of a block diagram illustrated. In Fig. 5 is schematically on the right that the above-mentioned vibratory transducer with exciter mechanism 16 and sensor arrangement 17, 18, which are necessary for the measuring principle of the transducer coils are drawn symbolically.

p0076[0072] The first measurement signal S and the possibly present second measurement signal S, each of which typically one of the instantaneous oscillation frequency of the measuring tube has corresponding signal frequency 13 are, as shown in Fig. 2, one of the field device electronics 20 provided, preferably digital , evaluation unit 50A of the operating and evaluating circuit supplied. The evaluation unit 50A serves a to be detected process variable, in this example, the mass flow rate, density, viscosity, etc., currently representing measured value, X, esp. Numerically to

p0077M determine and in a corresponding exit of the convert the operating and Auswerteschaltun g can be tapped measured value signal x. Whereas in the measurement shown here, the density or viscosity transducer entirely with reference to a single one of the measurement signals s, s are determined to be for the case where the mass flow is to be measured, in the manner known to those skilled both measurement signals s, s used to so, for example in the signal-time domain or the signal frequency quenzbreich to determine a corresponding mass flow with the phase difference. [0073] According to one embodiment of the invention, the evaluation unit 50A is under

p0078Using a provided in the field-device electronics 20 microcomputer .mu.C realized, which is programmed in a similar manner such that it determines the digital measured value XM based on the measurement signals delivered by the sensor arrangement 17, 18th For the realization of the microcomputer, for example, suitable microprocessors and / or signal modern processors may be used. As further shown in FIG. 5, the evaluation unit 50A further comprises at least one A / D converter, via the one of the sensor signals s, s, or, in particular, for Coriolis mass flow sensors common to a previously s of the two sensor signals s derived signal difference is supplied digitized microprocessor. The part of the evaluation unit 50A produced and / or received measurement or operating data may also in corresponding digital data memories RAM, EEPROM are stored volatile and / or persistent.

p0079[0074] As already mentioned, the operating and evaluating circuit 50 further includes the feeding of the exciter arrangement 16 with said excitation current i serving driver unit 50B that virtually represents a control loop together with the measuring tube thirteenth This control loop is designed so that it electrically adjusts both to the mechanical resonance frequency of the excited vibrations of the measuring tube 13 and to the predetermined reference signal Sr by means of the amplitude of these vibrations. The driver unit 50B can in the usual manner by means of a phase-locked loop, a so-called PLL, may be formed for the electrical regulation of the resonant frequency as well as the phase position of the driving signal and by means of a corresponding amplitude control stage for the electrical regulation of the amplitude of the driving signal and in this respect also the vibration amplitude.

p0080shown [0075] in Fig. 5 represents the driver unit 50B also in contact with the evaluation unit, esp. the already mentioned microprocessor .mu.C, from the driver unit 50B such as the required operation data, such as the excitation frequency currently set, and / or the one for the excitation current currently adjusted amplitude and, if necessary, adjusted phase, or to which the driver unit 50B internally generated setting signals and / or parameters, esp., information about the selected excitation current i and / or the EXC to the measuring transducer fed excitation power P sends , The operating data for the driver unit 50B, excitation frequency, amplitude and / or phase, can be both absolute and relative requirements specifications. Alternatively or in addition to the transferred to the driver unit 50B operating data can re- incremental or decremental change of excitation frequency, amplitude and / or phase present. In addition to the microprocessor .mu.C, the operating and evaluating circuit 50, for example, also a producing the driver signal signal generator serving, for example, a digital signal processor or an appropriately configured as a signal generator programmable logic device, esp. FPGA having.

p0081[0076] FIGS. 6 to 12 are embodiments for the driver unit 50B by type of block diagrams, which are particularly suitable for use in a designed as an intrinsically safe instrument and / or 2L-meter field device.

p0082[0077] In a first variant is a demodulation pd is provided as input signal one of the sensor signals supplied by the sensors 17,18 or z. B. also supplied to their sum. Thus, the demodulation stage pd is on the input side with one of the sensors 17,18 connected - shown in Fig. 6 that the sensor 17. The demodulation stage pd serves continually to determine an oscillation amplitude of Meßrohrvibrationen. Further serves the demodulation pd to an output signal z. B. to provide a simple DC signal, that these detected vibration amplitude represents. But according to a preferred embodiment of the invention in the demodulation stage pd a peak detector for the input signal is provided. Instead of this peak detector may, for example, but also a synchronous rectifiers are used for detecting the vibration amplitude, which is clocked by an input signal to the phase reference signal. A first input of a comparison stage sa is connected to an output of the demodulation stage pd; a second input of the comparator stage SA is supplied to an adjustable reference signal Sr, which sets an amplitude of the vibration of the measuring tube thirteenth The comparison stage sa determines a deviation of the output of the demodulation stage pd from the reference signal Sr and outputs them as a corresponding output signal. This deviation can be determined and passed on also using a ratio of detected and predetermined vibration amplitude inform a relative amplitude error as using a simple difference between the sensed and predetermined by the reference signal Sr oscillation amplitude inform an absolute amplitude error or z. B.. A first input of an amplitude modulation stage AML, the input signal of the amplitude demodulation stage pd and a second input is supplied with the output signal of the comparison stage SA. The amplitude modulation stage aml serves to modulate the input signal of demodulation stage pd with the output of the comparison stage sa amplitudes. In this case, for example, one of the sensor signal S, the sum of the two sensor signals s, s or even a to substantially pro- -proportional. for example by means of an appropriate, esp. digital, signal generator artificially generated signal as an input signal and thus serve as in frequency quite variable carrier signal to which the generated by the comparison stage sa, its amplitude varying error signal is modulated The error signal represents namely represent the deviation of the instantaneous amplitude of vibration of the measuring tube 13 differs from its represented by the reference signal Sr target oscillation amplitude. Furthermore serves the amplitude modulation stage aml to supply the driving power transmitting driver signal for the exciter assembly 16. For this, the amplitude modulation section to a corresponding stage ps for amplifying the modulated carrier signal with the modulation signal. For the purpose of amplitude modulating the carrier signal with the modulation signal in the amplitude modulation stage AML further a multiplier is provided ml. See Fig. 6.

p0083[0078] FIG. 7 is partially shown the circuit diagram of a second variant for the driver unit 50B according to the second variant of the invention in the manner of a block diagram. The embodiment of FIG. 7 differs from that of FIG. 6 differs essentially in that instead of being provided by the amplitude modulation stage am a pulse width modulation stage pwm with an external AC signal clocked pulse duration modulator pm. The pulse duration modulator pm, as shown in Fig. 7, operated at a constant positive first DC voltage + Ul and lies at circuit ground SN. A first input of the pulse duration modulator pm - which is the carrier signal input - the input signal of demodulation stage pd is supplied. Thus, this first input is connected to one of the sensors - shown in Fig. 7, the back of the sensor 7. A second input of the pulse duration modulator pm - that is the modulation signal input - the proportional to the determined amplitude error error signal is supplied. The output of the pulse duration modulator pm is in turn connected to the input of an output stage ps', the exciter mechanism 6 supplies the output side with a corresponding drive signal. The 'delivered by the power amplifier driving signal PS is in this case a square wave signal, that is clocked with a signal frequency of the input signal of the amplitude demodulation stage pd and having a modulated with the output signal of the comparison stage sa pulse width.

p0084[0079] FIG. 8 is partially shown the circuit diagram of a third variant of the driver unit 50B in the manner of a block diagram. The embodiment of Fig. 8 differs from that of Fig. 6 differs in that instead of the multiplier, a comparator kk and a DC-DC converter are provided de ml, which supplies at least one of the excitation current i exe driving driver voltage. The

p0085Amplitude of driving voltage in turn is dependent on the output signal the comparison stage sa and therefore considered to be non-constant. Depending on the design of the driving voltage, the excitation current i, as mentioned above, bi-polar or uni-polar but also be. Therefore, the DC-DC converter de 8 delivers to a preferred embodiment of the invention shown in Fig. A driving voltage having a positive first potential + u and -u a negative second potential, wherein a setting of the potentials serving control input of the DC de the output of the comparison stage sa receives. The from the DC converter de delivered, in amplitude correspondingly adapted drive voltage is a dining excitation assembly 16 serving stage ps ", the pulse width modulation stage pwm applied as operating voltage. In addition, the stage ps" input is connected to the one output of the comparator kk. The comparator kk is operated at the constant positive first DC voltage + Ul and lies at circuit ground SN. An input of the comparator kk is supplied to the input signal of the peak detector PD. Thus, the comparator kk input side is connected with one of the sensors -. In Fig. 8 which is again of the sensor 17. In Figs 6-7 are each indicated by dashed lines, that instead of one of the sensor signals from the sensors 17,18 and the sum of the peak detector pd and the multiplier ml and the pulse width modulator PM or the comparator can be fed to KK; then the sensor signals are to lead an adder. Alternatively, however, a signal generated by the digital signal processor and connected thereto output D / A converter, in its frequency and phase to the sensor signal corresponding matched artificial signal may also, as already mentioned, be used. In Figs. 6 to 7 further dashed subcircuits are seen that represent preferred embodiments of the preferred exciter circuit. In a development of the driver unit 50B, a preamplifier vv is provided, which is the peak detector pd or possibly upstream of the synchronous rectifier. In another development of the driver unit 50B is an amplifier v provided which amplifies the output signal of the comparison stage sa before it enters as an error signal to the amplitude modulation stage am. Such an amplifier may be an operational amplifier op, whose non-inverting input is connected to ground SN, its inverting input via a series resistor wv to the output of the comparison stage sa and via a shunt resistor ws to the amplifier output is connected. The operational amplifier wired op is respectively above right in Figs. 6 to 7. In a next development of the driver unit 50B is an integrating amplifier vi is provided which amplifies the output signal of the comparison stage sa and integrated before it enters as an error signal to the multiplier m. Such an amplifier can 'Be, the non-inverting input is connected to ground SN, its inverting input via a series resistor wv' an operational amplifier op with the output of the comparison stage sa and via a series circuit of a shunt resistor ws' and a capacitor k to the amplifier output connected is. The operational amplifier wired op 'is to see 6 to 7 each right in the center of FIG..

p0086[0081] Another development of the driver unit 50B is in a differentiating and integrating amplifier vd amplifies the output of the comparison stage sa, differentiated and integrated before it enters as an error signal to the multiplier ml. Such an amplifier can be ", whose non-inverting input is connected to ground SN, its inverting input via a parallel circuit of a dropping resistor wv" an operational amplifier op and a first capacitor kl to the output of the comparison stage sa and via a series circuit of a shunt resistor ws " and a second capacitor is connected to the amplifier output k2. the operational amplifier wired op "6 to 7 respectively on the bottom right in FIGS. to see. By means of the arrows in Figs. 6-7 indicated that the respective amplifier V, VI, vd the place of the dashed square of q is set to, either between the output of the comparison stage SA and the second input of the amplitude modulation stage on or but between the output of the comparison stage sa and the modulation signal input of the pulse width modulation stage pwm.

p0087[0082] It is well within the scope of the invention that the functions of the individual subcircuits of Figs. Are 6-7 realized by corresponding analog or digital sub-circuits, in the latter case, for. Example, by means of a suitably programmed microprocessor, which this supplied signals are above where appropriate to undergo analog / digital conversion and the output signals of a digital / analog conversion.

p0088[0083] FIG. 9 is a circuit diagram of a first embodiment of an output stage ps is illustrated, which can be used for example in the amplitude modulation stage am of FIG. 6. An operational amplifier ov is operated at a positive and a negative, respectively constant DC voltage + U, -U and wired as follows. An inverting input is connected via a first resistance wl at circuit ground SN and a non-inverting input via a second resistor w2 at the output of multiplier ml. An output of the operational amplifier ov is the interposition of a third resistor w3 to a first pole ppl a primary of a transformer tf connected; a second pole pp2 the primary winding is connected to ground SN. The transformer tf also has a secondary winding, the spl means of its two poles, sp2 on the exciter connected arrangement 16th The primary winding has a primary number Nl and the secondary winding a secondary number N2. The transformer TF is a current step-up transformer, and has a transmission ratio N1 / N2 of, for example 20: 1 is connected to the inverting input of the operational amplifier via a fourth resistor ov w4 on the first Polppl the primary winding.. The non-inverting input is connected via a fifth resistor to the output w5. The five Wi- derständewl, w2, w3, w4, w5 have appropriate WiderstandswerteRl, R2, R3, R4, R5. The resistance R is equal to the resistance R2 and the resistance R4 is equal to the resistance R5 to choose. The current flowing in the exciter mechanism 6 alternating current i is as follows, when the output voltage of the multiplier is designated m with order:. R5N1 1 = to m Rl R3 N2 In Figure 10 is a diagram of a preferred second embodiment of an output stage ps' which the can be used for example in the pulse width modulation stage pwm of FIG. 7. The "core" of this embodiment of the output stage, which is a complementary push-pull output stage is a series circuit of the controlled current path of a P-channel enhancemen insulated gate field effect transistor P with an N-channel enhancemen insulated gate field effect transistor N which are briefly referred to as transistors. At the connecting point of the controlled current paths of the exciter arrangement 16 is connected. Each of said controlled current path, a protective diode DN, DP connected in parallel, wherein the respective cathode is located on the positive point of the respective transistor. The P-transistor-side end of the series circuit is located on a constant positive second DC voltage + U2 and their N-transistor-side end to a corresponding negative DC voltage - U2. The gates of the transistors N, P are connected together and to an output of a comparator kk '. The non-inverting input of the comparator kk'liegt at the output of pulse width modulator PM. See Fig. 7. The inverting input of the comparator kk 'is connected to a tap of a voltage divider consisting of a resistor RL and a resistor R2. The cons stand 1, r2 have the same resistance values ​​and lie between the positive DC voltage + Ul and ground SN. The cons stand 1, r2 and comparator kk 'serve to balance the output of the pulse duration modulator pm with respect to half of the DC + Ul. The exciter arrangement 16 thus obtained at each positive-going zero crossing of the output signal of the sensor 17 or the sum of the output signals from the sensors 17,18 a positive current pulse and negative-going at each zero crossing of the output signal of the sensor 17 or the sum of the output signals from the sensors 17, 18 a negative current pulse supplied. The respective duration of these current pulses arises automatically so that the predetermined reference signal Sr by the vibration amplitude of the measuring tube is achieved thirteenth

p0089[0085] FIG. 11 is a circuit diagram of another embodiment of an output stage ps "is shown which can be used for example in the amplitude modulation stage aml according Fig. 8. The" core "of this embodiment of the power amplifier, which is a complementary push-pull output stage again , is also here, as in Fig. 10, a series circuit of the controlled current path of a P

p0090Channel enhancement-mode insulated gate field effect transistor P'mit an N-channel enhancement-mode insulated gate field effect transistor N ', which are again referred to hereinafter shortly as transistors. At the connecting point of the controlled current paths of the excitation device 6 is connected. Each of said controlled current path, a protective diode dn ', dp' connected in parallel, wherein the respective cathode is located on the positive point of the respective transistor. The P-transistor-side end of the series circuit is + u and their N-transistor-side end to the dependent from the output signal of the comparison stage sa negative DC voltage -u the dependent from the output signal of the comparison stage sa positive DC voltage. The gates of the transistors N ', P' are "connected. The non-inverting input of the comparator kk" together and to an output of a comparator kk is located at the output of the comparator kk, see. Fig. 8. The inverting input of the comparator kk " is connected to a tap of a voltage divider consisting of a resistor r3 and a resistor r4. the resisters e r3, r4 have the same value and are connected between the constant positive first DC voltage + Ul and ground SN. the resistors r3, r4 and the comparator kk 'serve to balance the output of the comparator kk with respect to half of the DC + Ul. The exciter arrangement 16 thus obtained during each positive half cycle of the output signal of the sensor 17 or the sum of the output signals from the sensors 17,18 a positive current pulse and during each negative half cycle of the output signal of the sensor 17 or the sum of the output signals from the sensors 17,18 a negative current pulse is supplied. The respective amplitude of these current pulses is of the dependent from the output signal of the comparison stage sa direct voltages + V, -V in turn dependent, so that the position predetermined by the reference signal Sr vibration amplitude of the measuring tube 13 is automatically adjusted.

p0091. [0086] In Figure 12, finally, is an embodiment of a hybrid - so proportionately digital and analog operating proportionately - driving circuit 50B schematically represented as a block diagram. The drive circuit 50B comprises a digital signal generator, which serves generated by the microcomputer 50A, esp. Numeric, default values ​​for the individual parameters of the excitation signal, for example an amplitude Converting the excitation current i, a phase of the excitation signal and / or a vibration frequency exc supply thereof into a corresponding digital vibration signal. The individual parameters can, as already mentioned, has to be passed, for example, as absolute values ​​and / or as an incremental or Dekrementalwerte to the driver unit 50B. [0087] As already mentioned, the field-device electronics and thus also the

p0092Field device from an external electrical power supply 70, for example, a remote transducer supply or the like, fed, which is connected via at least one pair of electric lines 2L to the field device, or more specifically with the field-device electronics 20th The transducer supply turn can for example be connected via a fieldbus system with one in a stationed in a process control waiting parent process control system. In the embodiment shown here, the field-device electronics is further, as in numerous applications industrial measurements and automation technology often the case, at least temporarily electrically operatively connected to the external electrical power supply solely via a single pair of electric lines 2L. So then the field device electronics, accordingly, is supplied on the one hand this is a pair of leads with electrical energy. On the other hand it is provided that the field-device electronics the measured value at least temporarily generated XM also arranged on the single pair of electric lines 2L to a resident of the external electrical power supply 70 and / or to the power supply electrically coupled external evaluation 80 sends. can 2L pair of electrical cables for example, with a supply current I feeding energy source 71, such as a battery or fed on a plant-internal supply network DC voltage source, and a measuring resistor RM be connected in series - The transducer supply and field device connecting - here only. , The energy source 70 drives the supply current I and thus supplies the field device electronics

p009320 with the electric power required for its operation. The measuring resistor R is also provided with two measurement terminals 72, 73, where the the value X

p0094MM currently representing supply current as a current proportional voltage U is tapped. The voltage U can, for example visualized locally or on a higher measured value are supplied. The - only here - pair of electric lines 2L, for example, as so-called two-wire current loop, especially 4 mA -. 20 mA current loop, or as a connecting line to an external digital fieldbus, for example, a PROFIBUS PA or a FOUND ATION HELDBUS be formed ,

p0095[0088] In a further embodiment of the invention is therefore further provided zumodulieren current measurement XM to the supply current I on. examples for example, by an instantaneous, especially the currently determined by means of the field device measurement. a between 4 mA and 20 mA lying value set, amperage of the electrical where designed as two-wire current loop pair lines 2L flowing supply current I represented.

p0096[0089] According to another embodiment of the invention that the field device at least temporarily with an external command and control unit, for example, a pendant or a speicheφrogrammierbare controller (PLC), communicates via a data transmission system, for example, field device-specific exchanges data. For a communication circuit COM is provided in the field-device electronics 20 further, which controls communication via data transmission system and controls. In particular, the communication circuit and internal field device parameters in signals serves in addition to the measured value X as environmentally

p0097M zuwandeln, the electrical lines on the pair 2L are transferable, and then inject it. Alternatively or in addition to the communication circuit COM can also be adapted to receive transmitted externally through the pair electric lines 2L field device parameters accordingly. As a communication circuit COM can, esp. For the above case where the field device is simply connected to the external power supply circuit during operation via two-wire current loop, z. B. an in accordance with the

p0098HART® field communication protocol of the HART Communication Foundation, Austin TX be working interface circuit that uses so FSK encoded higher-frequency alternating voltages as signal carrier.

p0099[0090] As seen from the comparison of FIGS. 1 and 5, field device includes electronics 20 for the adjustment and regulation of voltages and / or currents internally in the field device further comprises at least one through which the supply current I current adjuster IS for setting and / or modulating, esp. clocks of the supply current I on. In addition, in the field-device electronics 20, an internal power supply circuit 40 is provided, which abuts a divided by the terminal voltage U internal input voltage U of the field-device electronics 20 and serves to feed the internal operating and evaluating circuit 50 electrically.

p0100[0091] For detecting and regulating currently falling in the field-device electronics 20 voltages and / or currently flowing streams further includes the supply circuit 40 a corresponding measuring and control unit 60. In addition, the measuring and control unit 60 serves, in particular, for the above-mentioned case that the measured value XM is modulated onto the supply current I, also, one of the

p0101Operating and evaluating circuit 50 supplied, the measured value currently generated XM representative measured value signal x M in a current adjuster IS and therefore also comply

p0102Supply current corresponding to adjusting the first current control signal I implement. The measuring and control unit 60 forms so far, together with the current adjuster IS practically a current regulator - here called a linear series regulator - for the supply current. The current control signal I is in accordance with an embodiment of the alternate

p0103Invention designed so that the aforesaid flow controller is able to adjust the supply current I proportional to this, taking into account the currently measured value X determined. Alternatively or in addition to the current control signal I is designed so that the current controller to supply current I is clocked, for alternate example for the purpose of communication in binary code according to the standard PROFIBUS-PA. For generating current representative accordingly, esp. Essentially current-proportional, sense voltages I, 1, 1 are further 3_ist in l_ist 3_ist the supply circuit 40 corresponding, at least temporarily, from the power supply or it abgezeigten substreams 1, 1, 1 according flown through sense resistors R, R, R provided.

p0104[0092] At least for the above case in which the supply current is I modulated for purposes of illustration of the measured value X in its amplitude and due to the limited electric power of the external power supply that it delivered supply voltage U and, consequently, also the terminal voltage U with increasing supply current I drops accordingly or vice versa increases again with decreasing supply current I, the supply voltage U and so far also the terminal voltage U in its voltage level in advance not determinable manner is vague and so far as the operation to a large extent variable to watch. If the field device operates according to the above-mentioned, in the industrial measurement technology has long established standard of 4 mA to 20 mA, thus stands for the power supply in normal operation, only the current range below 4 mA and depending on the level of the supply voltage thus only about 40 to 90 mW (= milliwatts) of electric power permanently available.

p0105[0093] The supply circuit 40 has, therefore, as also shown in Figure 5 shows schematically, further input a voltage Steep 30 which -. Actuated by the measuring and control unit 60 - is provided for a primary or base voltage of the internal power supply serving internal input voltage U of the field-device electronics adjust as closely as possible to a predetermined, possibly in operation also varying voltage levels, and at least for the undisturbed normal operation, at the least, among other things, the terminal voltage U equal to a minimum voltage value U is K_min, also as constant and steady keep on this currently selected voltage level. The measuring and control unit 60 forms so far, together with the voltage Steep 30 an input voltage regulator for the internal input voltage U, which especially serves. To this possible to accurately adjust and broadly stabilizing. The voltage level of the internal input voltage U in accordance with an embodiment of the invention maintained so that the internal input voltage U, as well as in Fig. 13 schematically shown e, always is lower than the terminal voltage U. Here, the voltage may level at which the internal input voltage U is held by means of the aforementioned input e output voltage regulator 30, 60, are continuously changed during operation depending on the currently flowing supply current I, for example, essentially. Alternatively, however, the voltage level over a certain current range of the supply current is also possible, I and the extent to keep a corresponding voltage range of terminal voltage U constant and as shown in FIG. 13 indicated by the dash-dotted line drawn to gradually change, for example, exceeds or falls below specified thresholds accordingly for the supply current I and / or the terminal voltage U. According to a further embodiment of the invention is the input voltage regulator 30, 60 is designed so that the the voltage level after reaching a predetermined or predeterminable maximum voltage level U, in_max for example in the order of 15 V, despite allfällig further increasing the terminal voltage U, for example to about 20 V, is kept constant. Therefore, as far affects the input voltage controller 30, 60 not only as a voltage stabilizer for the internal input voltage U but also as a voltage limiter for this. To further internal sub-distribution of electric power to individual

p0106Components or subassemblies of the field-device electronics has this further comprises a stabilized internal input voltage U-converting first useful-voltage controller UR, which is at least intermittently flows through one, esp. Variable, the first current component I of the supply current I and which serves a predetermined on a , possibly also programmable, the first voltage level U in

p0107Nljsoll substantially constant controlled first internal useful voltage U in the field device

p0108nl

p0109Electronics 20 provide. in the supply circuit 40 a also the stabilized internal input voltage U-converting second useful-voltage controller UR variable, the second current component I of the supply current I is further provided, which at least temporarily, by an, especially. flowed through. The second useful UR turn serves to provide a variable over a predetermined voltage range second internal useful voltage U in the field-device electronics 20th The for the current consumption situation in the field-device electronics most suitable voltage level for the useful voltage U can be, for example, by the measuring and control unit 60 determined in consideration of a current consumption situation in the field-device electronics and communicated to inform a voltage control signal U to the Nutzsspannungsregler U , As useful-UR, UR example so-called switching regulator and / or unmetered linear regulator can be used during the voltage Steep 30 nor will the input voltage regulator realized for example by means of an in a shunt to internal input voltage U, for example by transistor and / or ALPA adjustable Zener diodes , shunt regulator iS can be formed.

p0110is [0095] Moreover, the input voltage regulator, as shown also in FIG. 5, designed such that it in normal operation at least temporarily by an, especially. variable, third current component I of the supply current I flowing through, wherein the measuring and control unit 60, a the voltage Steep 30 - here the shunt regulator IS - accordingly controlling the extent and also the third current component determining second current control signal I delivered. The current control signal I is at least for the

p01113_stell 3_stell

p0112Case which exceeds the part of the operating and evaluating circuit 50 currently actually required electric power from the internal in held substantially constant input voltage U and the currently set supply current I resulting, currently available in the field-device electronics 20 electric power, designed that it can be a conductive provided in the input voltage regulator transistor to a sufficient extent to allow a sufficiently high for the stabilization of the input voltage U part current I to flow. For this purpose, the input voltage regulator - here in voltage Steep 30 - a further embodiment of the invention, the dissipation of electrical energy and the removal of this arising thermal energy serving components, especially a semiconductor element with heat sink or the like, provided.. On the other hand, the current control signal I also designed so that it becomes larger conductor

p01133_stell stungsbedarf again decreased in the operating and evaluating circuit 50 to the voltage Steep 30 currently flowing partial current I.

p0114[0096] Further, as shown in FIG. 5, is provided in the inventive field-device electronics 20 and thus also the field device according to the invention that the operating and evaluating circuit 50 at least temporarily both of one of the at least in normal operation is kept constant substantially first useful voltage U GE

p0115Nl exaggerated, esp. The variable, the first useful current I and of one of the described

p0116Nl drove vary according serene second useful voltage U-driven, esp. Verän-

p0117N2 sary, second useful current I is flowing through it. This has the advantage that, at least

p0118N2 the controlling normal operation and thus a field device in gear holding assemblies and circuits of the field-device electronics 20, esp. The mentioned at least one microprocessor .mu.C, can be supplied with the electric power is always that they actually need currently. Accordingly, the invention is according to one embodiment, provided the above-mentioned microprocessor .mu.C and / or the aforementioned signal processor, at least partially with the kept largely constant in normal operation the first useful voltage U or derived from secondary

p0119Nl secondary voltage to operate. According to a development of this embodiment of the invention, the first useful voltage U or is derived from secondary

p0120Nl further därspannung at least partially, also the at least one provided in the operating and evaluating A / D converter as an operating voltage. According to another embodiment of the invention, at least also controlling the communication with the mentioned parent command and control unit and maintaining the components of the field-device electronics, in this case in addition to the microprocessor .mu.C, the communication circuit COM, at least in part by the first useful voltage U or one of them partitioned secondary voltage to

p0121Nl supply.

p0122[0097] Depending on which electric power can be effectively provided in the operating part of the external power supply circuit 70 as well as a function also of the actual power requirement of the above-mentioned manner already from the first useful voltage U-fed consumers can take individual, especially the generating the drive signal i serving components of the driver unit 50B, for example, it provides amplifiers, D / a converter and / or signal generators, etc., at least by the first useful voltage U or one of them be fed proportionately partitioned secondary voltage. see also refer to the FIG.

p0123nl

p012412. However, it has been found that if only with currently available microprocessors .mu.C and / or A / D converters and for required peripheral loading circuits in normal operation is already expected to permanent power requirement of about 30 mW, so that at least be connected in applications with a permanently available power of only 40 mW, so at a terminal voltage of 12 V (= V) or less, the aforementioned components of the driver unit 50B only in very small amount of the first useful voltage U

p0125Nl can without jeopardizing their desired high stability. In that regard, it is further provided according to an embodiment of the invention, individual components of the drive unit 50B esp. Permanently to operate only on the second useful voltage U. More particularly, second useful voltage U, as well as in Figure 12 is suitable.

p0126N2 shown is representative, as the operating voltage for the period specified in the driver unit 50B OpAmps. Accordingly, then the exciting current I for the magnetic field coil is substantially of the second useful voltage U, or a secondary voltage derived therefrom would be driven.

p0127[0098] In order to bridge transient voltage fluctuations from the power supply and / or for buffering of any short-term "overloads" the field device's internal power supply due to a higher internal conductor Arnold Böcklin stungsbedarfs, for example during start-up of the transducer or in describing the aforementioned persistent memory EEPROM, is in the operating and evaluating in accordance with an embodiment of the invention further includes the temporary storage of electrical energy serving, esp. capacitive memory circuit provided. The energy buffer C is illustrated in the embodiment shown here as part of the voltage controller 30, so that virtually permanently located on the internal input voltage U. However, a breakdown of the useful voltage U e Nl to avoid at least safe in normal operation, is in the interpretation of these supplied by the first useful voltage U assemblies and circuits in advance

p0128Nl of course ensure that the maximum electrical power is converted most equal to a minimum available during normal operation, electrical power and / or their currently converted electrical power is at most equal to a currently available power. According to another embodiment of the invention further provides that the second useful voltage U N2 during operation depending on a current

p0129Voltage level of the internal input voltage U of the field-device electronics is regulated. Alternatively or in addition to it is provided that the second useful voltage U

p0130N2 is controlled as a function of an instantaneous voltage level of the supply voltage divided over the field-device electronics dropping from the input terminal voltage U. Be advantageous it has here also demonstrated the internal input voltage U to regulate so that an existing between it and the terminal voltage U voltage difference is kept as constant as possible, at least in normal operation, for example, about 1 V. This allows, among other things, the input voltage U even under changing operating temperature of the current controller IS e __ 1 or even the entire current controller and a concomitant change in its respective transfer characteristic comparatively accurately adjust so easily to achieve a very robust control for the internal input voltage U. The control can be realized, for example, by means of 60 provided for in the aforementioned measuring and control unit differential amplifier having a correspondingly derived from the internal input voltage U e Sense voltage of a corresponding derivative of the terminal voltage U sense voltage subtracted. Alternatively or in addition thereto, the second useful voltage U as a function of an instantaneous current of at least one of the three sub-streams 1, 1, 1 regulated. For example, may be controlled depending on the instantaneous current of the third part of the current I, the second useful voltage U, which practically represents a currently existing in the field-device electronics surplus power according to the current input voltage U. As parameter in this case is in particular also the voltage regulator controlling the extent and also the third part of current I-determining second current

p01313

p0132Control signal I adapted.

p01333_stell To establish and / or monitoring a current operating state of the field-device electronics are in accordance with another embodiment of the invention further includes means for comparing sloping in the field-device electronics electrical voltages and / or current flowing in the field-device electronics electrical currents with predetermined, esp. adjustable thresholds provided. This means for comparing voltages and / or currents can be formed as an integral part of the aforementioned measuring and control unit of the power supply circuit, for example. According to one embodiment of the invention, the means are adapted to compare that part of the field-device electronics at least then an insufficient supply of the field device electronics signaling alarm signal x generated when falling below one for the second pwr_fail

p0134Useful voltage U N2 predetermined minimum useful voltage by the second useful voltage U and an undershooting of the third current component I pre-

p0135^{V b} N2 3 given minimum partial flow limit can be detected by the third current component I. To detect the third current component I can as a minister in Eingansspannungsregler 30, 60 provided in accordance with Part-carrying the current I sense resistor R, which provides an essentially current-proportional sense voltage. According to another embodiment of the invention the measuring and control unit 60, the voltage Steep 30 controls by means of the current control signal / so that the

p01363_steü third current component I, esp. Only flows when the second useful voltage with at least one associated reference voltage comparative comparator signals an exceeding of a predetermined for the second useful maximum useful voltage limit by the second useful voltage. The means for comparing voltages and / or currents may be, for example, simple comparators comparing the respective sense voltage with an associated, internally generated for example by means of the input voltage U, the e respective threshold proportional reference voltage.