Circuit enabling external devices to communicate with central/decentralised data processing system by means of a bus

The invention relates to a circuit for communication External field devices with a data processing system, In particular a monitoring and control system via a 2-wire field bus, according to the preamble of claim 1.

Such circuits are used, for example, in process engineering Used to connect external devices, for example "smart" Sensors and actuators, to the central or decentralized Monitoring and control system.

As fieldbus systems, for example, HART are used in sensor technology (Righway Addressable Remote Transmitter), the DIN measuring bus, the PROFIBUS (PROCESS FIELD BUS), FIP (Flux Information Processor Or also Factory Instrumentation Protocol), the IEC fieldbus and Further common. The transmission of the data takes place The fieldbus is partially binary, for example over standardized Digital signals, partly also analog. For example, The data transmission is performed binary by the PROFIBUS, While for HART the measured value is analogous to a superimposed Amplitude - modulated communication signal to the Data processing plant. In many cases Is also a power supply to the external device via the Field bus system.

From the DE publication "Neutrale Buslinie" Fairs and 32, No. 4, April 1, 1996, page 24, bus terminals go And fieldbus couplers which provide the adaptation Of different fieldbus systems to an internal data bus of the Bus Terminals.

EP-A-0 654 742 discloses a circuit for communication Of peripherals with a computer system bus Which is responsible for the communication via known means in the Data processing technology For example PCMCIA-EISA-PCI-VESA bus systems. Through this interface the data communication is over Different bus systems that are common in data technology possible.

The object of the invention is to provide a circuit for the Communication of external field devices with a central or Decentralized transmission and control system via a Two-wire field bus in such a way that not only one Automatic detection of fieldbus systems, but also one Complete adaptation to these fieldbus systems, in particular Even when the power supply of the external field devices is over The field bus.

This task is used in a circuit for communication External field devices with a central / decentralized Monitoring and control system via a two-wire field bus According to the invention, is solved by the features of claim 1.

Advantageous embodiments of the invention are subject matter Of the subclaims.

For example, to protect the circuit, transmission circuits are used Which have a galvanic decoupling Of the current / voltage supply to the circuit Connected external device (sensor, actuator) to the To ensure explosion protection.

There is also galvanic separation of the current circuit Of the external device (sensor circuit) from the supply / communication circuit Of the circuit, ie The circuit intrinsically safe, the data transmission From the external device to the microcontroller via one Digital interface, preferably via a galvanic decoupled I²C-bus, instead.

It is also advantageous that the circuit is the use Of bus systems, both on a digital As well as on analogue data communication Based. Also in this respect is the arbitrary usability Of different external devices.

The following description of preferred embodiments the invention serves in conjunction with be iliegender Drawing of the detailed explanation. Show it:<dl tsize="6" compact="compact"><dt>FIG</dt><dd>Schematically a circuit according to the invention For communicating external devices with a Central data processing system Bus;</dd><dt>FIG</dt><dd>The detailed construction of the embodiment shown in FIG Circuit according to the invention and</dd><dt>FIG</dt><dd>Schematically the circuit diagram of external devices, Which is connected to a central data processing system In a manner known per se Buses are coupled.</dd></dl>

FIG. 3 is a schematic representation of a Central data processing system 1, to which In a manner known per se, several different ones External field devices 2, for example sensors or Actuators, via different fieldbuses 3 are.

The field devices 2 can be connected directly via the field bus 3 Can be connected to the data processing system 1, it But also a plurality of field devices 2 can first be connected via a Field distributor 4, which may be, for example, a multiplexer Can be connected, this field distributor 4 For its part via a field bus 3 with the data processing system 1. The data processing plant Can also be performed by a memory-programmed circuit (PLC), a process control system (PLS), a personal computer (PC) or a so-called hand-held terminal (HHT).

When several different field devices 2, Each requiring a different field bus system 3 For their connection to the data processing system 1 Different types of field buses 3 may be provided. If these different types, such as HART Or PROFIBUS and the like. Are not present, so is it Not possible between external devices, this Bus type and the data processing system 1 The existing buses 3 to make a data connection.

The basic idea of ​​the invention is to provide a Circuit, which is independent of the used Fieldbus system can recognize the corresponding bus protocols And to make the necessary adjustments so that: The field device 2 to any field bus system 3 without External measures eg actuation of switches or the like. Can be coupled and thus independent of the particular one used Field bus system 3.

As is apparent from FIG. 1, in which a circuit for the Communication of external devices 2 with a central Data processing system 1 via bus systems 3 schematically , The circuit substantially comprises A processing unit, for example a microcontroller 6, current / voltage supply circuits 7 and A display 8.

The external field devices 2 can be, for example, pH sensors, Conductivity sensors and the like. Be In explosive and non-explosive environments Environment can be arranged.

For use in explosive atmospheres the Entire circuit is intrinsically safe. For this it is Required that both the current / voltage supply Of the external devices 2 through the current / voltage supply circuits 7 as well as the data exchange of the Data acquired by the external devices 2 with the Microcontroller 6 via circuits 5, which A galvanic decoupling of the external devices 2 from The current / voltage supply circuit 7 and the Microcontroller 6.

Circuit for communication of external devices 2 By means of a central data processing system 1 A bus 3 is shown in more detail in FIG.

As shown in FIG. 1 and FIG. 2, circuits are circuits 5 to ensure the intrinsic safety of the circuit Provided.

Filter and overvoltage protection circuits 11 Not just a filtering of the by way of example A two-wire technique known per se Supply and data signals Also that no interfering voltages / currents from the Circuit can reach the data bus 3; they Thus enabling the use of the entire circuit in FIG Explosive environment.

The input signals are first passed through the circuits 5 as well as the filter and surge protection circuits 11 of a connection unit (MAU, English Medium Attachment Unit) 12. This connecting unit 12 serves Filtering the input / output signals, in the case of Analog signals for their conversion into digital Signals.

The signals pass from the connection unit 12 via a Modem 14 to the microcontroller 6 connected, for example, to the microcontroller 6 An external keyboard 16 and the display 8 or Is also connected to an EEPROM 20 via connection lines Is. The microcontroller 6 is - decoupled via a Digital interface 17, for example an I²C-bus 17 - is connected to a transmitter 22, via which a PH, temperature, conductivity measurement or the like. By means of a sensor (not shown).

The connection unit 12 also comprises a Controllable current source or sinker 12a for adaptation The current / voltage ratios of the controllable device And to the internal current / voltage supply of the whole Circuit.

Furthermore, in the connection unit 12, Microcontroller 6 via the modem 14 Summing amplifier 12b for outputting to the external one Device and the bus adapted communication signals and For controlling the current source / current sink 12a.

The circuit automatically detects the signal at its input Existing bus and takes an adjustment of the external Field device on this bus 3.

It is, for example, possible, by means of the circuit, Digital transmission of the data, as they do In which PROFIBUS is present, as well As an analogue data transmission, as it does For example in the known HART bus.

In this case, the circuit is switched on, Connection unit 12 of the modem 14 and the microcontroller 6 as well as the controllable current / voltage supply circuit Has detected which bus 3 is at the input To the different ones Bus systems - for example To a current value between 4 and 20 mA, depending on the Measured value, in the case of using the HART bus, Or to the corresponding current and voltage values ​​of the Digital signal transmission in the case of PROFIBUS.

Finally, it should be mentioned that the connection unit 12, The modem 14 and the microcontroller also form part of a Single integrated circuit.