Multimeter having at least three input connections.

The invention relates to a multimeter said in the preamble of claim 1 is known.

Multimeters are the generalists among the meters and enjoy because of their versatile applicability in laboratories and workshops but also for hobbyists great popularity. The spectrum of the measured variables, which is covered by many of these devices ranges from voltages above currents, resistors, level up to frequencies, just to name a few. The measurement circuits that are needed for detecting the different measured variables, vary considerably in some cases, which means that for the different variables also must be different input circuits for measurement.

The versatility of the multimeter also poses dangers. Thus, it is important that before each measurement the right, the associated measured variable to be examined input circuit is connected. If, for example the mains voltage are measured and is inadvertently left the input circuit is turned on, which is provided for measuring currents, so the can for the multimeter, sometimes even for the operator, have serious consequences if the mains fuse does not switch off fast enough. As envisaged in the multimeter device fuse is not enough in most cases, in order to disconnect the multimeter from a high-energy Spannungsgquelle as occurring when opening the circuit arc bridges the device fuse.

Similar problems and dangers can also in other combinations, in which a measured variable meets a wrong input circuit, for the measuring object, the multimeter and the operator arise. But even when a service error results no immediate danger, it can still lead to an indirect threat if, for example, the display of the multimeter, the absence of a test voltage simulates because an input circuit has been connected, the not in service, so do not was connected to the measuring system. By feigned absence of voltage, the operator is tempted at times to him hazardous actions.

what to look for, so as to avoid such incorrect operation at a multimeter, depends on the structure of this device. In many multimeters the various input circuits have a common input circuits all first input terminal and a separate of each measuring circuit associated with the associated process variable corresponding second input terminal. Usually associated with each measured variable in turn multiple ranges such as the measurement quantity "Voltage" the ranges 1, 3, 10, 30V, etc. The input circuit in this case has a voltage divider, at which all voltages divided down to values ​​or be increased by amplification, therefore stand to the measuring system adjusted values ​​available.

For switching of the voltage divider to a desired voltage measuring or switching of the shunt to a desired current measuring range using a measurement range. When operating the meter so you have to ensure that the measurement range is set to the process variable to be measured. At the same time it must be ensured that the input side to the multimeter test leads with the right input terminals and thereby connected to the correct input circuit.

It is obvious that can be forgotten in less concentrated work, especially by non-professionals, one of the two operating handles, then connect either the incorrect input circuit, or an incorrect measuring range is switched.

Of course, one has tried to keep up with additional safeguards the dangers of incorrect operation within limits. The protection circuits used employ passive and active relay switches controlled semiconductor switches, with transistors and thyristors and fuses of a particular type. Despite the sometimes very high cost, it is possible with prior art techniques, however, by no means always, disable powerful power sources safely inside the small, available in the event modern multimeters space in case of error. Reducing the hazards thus can only be achieved if the incorrect operation is largely excluded.

An attempt this task by solving that one replaced the plugging of the test leads by switching the input circuits was. This, although the operation of the meter was somewhat relieved, but not eliminate the problem. Thus, the switching of the input circuits can either be done by an additional input circuit switch or additionally acquired by the measurement range. An additional input circuit switch shifts the problem only to a different component, since now it must be ensured with the same attention to the fact that both the input circuit switch and the measurement range are set to the measured variable to be examined. In contrast, represents a summary of all switching functions on measurement range, that it must be able to turn out very small and large loads, which in turn results in a considerable increase in the price of this device to follow. An additional consideration is that the thus achieved reduction in the number of the controls does not necessarily make the operation much safer, because even a single switch can still be brought to a wrong switch position, which then inevitably to connect also an incorrect input circuit with corresponding consequences resulting , To this extent forced to the correct position of two control elements can have, lead to increased attention eighth.

The object of the invention is to provide a multimeter according to the preamble of claim 1, which manages with a measurement range, which must turn very small benefits for submission to the measurement system, the operator, however, prevents them to join such an input circuit associated with a measured quantity is, which has not been set on the measurement range switch.

This problem is solved by the features characterized in claim 1. Expedient refinements and developments of the subject matter recited in the dependent claims.

Since according to the invention a locking device with the respective switching position of the measurement range switch is coupled, it is possible to lock the input terminals with respect to a measuring signal receiving contact so that in each case only a certain input terminal is contactable. The input terminal of this associated process variable corresponding to the coupling of the set on the measurement range switch variable. The coupling with the measurement range switch can be performed on both mechanical and electrical manner. In both cases, the user is in front of it protected, erroneously turn on an input circuit for a different measurement quantity than was given also the measurement range, thereby increasing the operating safety of the meter substantially increased.

A locking device particularly simple construction can be realized by mechanical means when connected to the measurement range locking guide is provided, the location of which, upon actuation of the measurement range with respect to the input terminals so changed that they contacting certain input terminals through the preferably designed as a plug contact parts of the measuring lines prevented. The rigid coupling between measurement range and locking guide a substantial safety advantage is achieved insofar as in the connected measuring lines the inserted plug fix the locking guide in position and thus the measurement range is protected from unintentional switching by the coupling elements. The user is thus forced to another measured variable to consider before switching the plug and thereby release the locking device. Through the opening of the input circuit is ensures that can be switched from the power supply state, so no switch contacts endangering currents. After switching in turn can only such input terminal can be contacted, which is assigned a predetermined measurement range with the measured variable.

The locking guide will be advantageously produced from an insulating plastic and position it so that it can block the insertion direction the receiving channel of at least one of the input terminals configured as sockets transversely. For the detailed design of a mechanically acting locking device, there are any number of variations, which can not all be mentioned here. It will adjust the locking guide based on the nature and the structure of the corresponding measurement range, and accordingly is preferably used a rotary or slide link for the application. In the locking detent recesses are provided, their positioning with the switching position of the measurement range so correspond that the recesses each release the receiving channel of the input port that is assigned to the set with the measurement range variable.

It is further provided to arrange the movable locking guide in the area of ​​the input terminals in a provided for their reception and storage recess of the top wall of the housing. A manually operable actuating portion of the measurement range may act on the locking guide that these changes its position to the input terminals accordingly.

The coupling between the measurement range and the locking guide is expediently carried out in that the operating part of the measurement range in the same or a parallel plane lying, as designed as drebbewegliches element locking guide is arranged and provide coupling elements for mutual engagement. Suitable measures can ensure that a forced entrainment of the locking guide is only in a portion of a switch element executable rotation.

Solutions that do not have the full range of rotation of the measurement range there is a rigid coupling with the locking guide, have the sense of being able to switch to different ranges of the same measured variable, without creating changes in the position of the locking guide something.

A trained on the actuation part switch wheel has at least one tooth, with which it can intervene in another tooth of the rotatable locking guide, preferably in the groove of a two-pronged fork, as in a Geneva mechanism.

The releasing of certain input terminals provided in the locking detent recess must be designed so that it corresponds with the switch to the respective position of the input terminal. When configured as a rotatable disc locking guide recess may be a round hole, when the input terminals are at a corresponding arc. If the input terminals on the other hand, as usual, on a straight line, so the cut is to be designed as an elongated hole to equalize the pressure developed during the rotation offset.

Instead of a one-piece locking guide with a corresponding recess and a locking guide formed from a plurality gate valves can occur. Each of these locking slide is stored so that it can be brought by a displacement against the force of holding him in rest position by a spring driven by the measurement range switch cam slider into the input terminal locking position. The operating part of the measurement range can act by a translation or rotation of the cam slider.

An electrically operating blocking device is set up so in principle that at least one of the input terminals, preferably designed as plug-in sockets is provided with an electromagnetically operable locking element that must be arranged so that it can assume a contact-preventing locking position. For example, the receiving channel of a plug socket is blocked when set on the measurement range switch measured variable with the input terminal associated measurement variable does not match. Here again, a coupling of the electromagnetically operated locking element with the measuring range switch is required which manages characterized in that a trigger circuit is passed via a switching path of the measurement range.

This problem is solved by the features characterized in claim 1. Expedient refinements and developments of the subject matter recited in the dependent claims.

Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>Multimeter in plan view with rotatable locking guide,</dd><dt>FIG. 2</dt><dd>Multimeter according to Fig. 1, from the side, partly in section along the section line II</dd><dt>Fig. 3</dt><dd>Switch element in plan view,</dd><dt>Fig. 4</dt><dd>Switch element laterally on average,</dd><dt>Fig. 5</dt><dd>rotatable locking guide in plan view,</dd><dt>Fig. 6</dt><dd>rotatable locking guide laterally,</dd><dt>Fig. 7</dt><dd>Locking guide with individual gate valves,</dd><dt>Fig. 8</dt><dd>Measurement range as a sliding switch having a plurality of gate valves as locking guide</dd><dt>Fig. 9</dt><dd>Measurement range as a sliding switch with a single locking guide</dd><dt>Fig. 10</dt><dd>Range switch with electromagnetic locking device,</dd><dt>Fig. 11</dt><dd>Receptacle with electromagnetically driven locking bolt.</dd></dl>

Of the various ways to couple a measurement range with a mechanically acting locking device, is a first embodiment in FIGS. 1 and 2 in detail. In the area of ​​a cover plate 21a of a multimeter housing 20 can be seen a display 28, a plurality of operating elements 29, a measurement range switch S and input terminals 1,2a-2c. Coupled with the range switch S locking guide SK 1 is represented by a dotted line in Fig., Since it is located in a not identifiable from the outside recess 22 in the top wall 21a.

Further details of the measurement range switch S, more specifically its operating section 5, which are also for its interaction with the locking guide SK important will become apparent from the detailed drawings Fig. 3 to Fig. 6. At the operating part 5 of the measurement range S includes 5d a ring-like shaped switch wheel 5a, a toggle switch 5b, designed as a pin first coupling element 5c and serving as a carrier for the contact carrier plates of the measurement range is not shown switching threshold value. The switching threshold value 5d is connected to the switch wheel 5a by acting as a bridge switch knob 5b. The molded-on switch wheel 5a peg-like first coupling element 5c permits at a second of the shifting gate SK associated second coupling element 25 a the two parts together coupling engagement.

The coupling device operates in the manner of a one-armed Maltese cross with a two-pronged fork 25a, 25b, 25c form a the pin-like first clutch element 5c receiving guide groove. If a predetermined rotational angle is exceeded during a rotational operation of the switch wheel 5 so as to slide the pin-like first clutch element 5c of the guide groove 25c out, and thus solves the rigid coupling between the two parts. In this area it is possible the measurement range switch S continues to rotate and where applicable, to other, usually belonging to the same process variable measurement ranges, while the locking guide SK remains in its end position. Only when turning back the switch wheel 5a engage the first coupling element 5c, upon reaching the second coupling element 25 back to this one and ensures that the locking guide SK is entrained at least until the next shift position.

In the present example of FIG. 1 has the meter 3 each specific measured variables A, B, C associated with the input terminals 2a, 2b, 2c, and a common to all the three input terminals of input terminal 1. The locking guide SK has a recess 3, depending on the switching position of the measurement range S a certain input terminal 2a or 2b or 2c releases. The measurement range switch S was adjusted to the measured quantity B and in this position is the locking guide SK only the input terminal 2b free. If the measurement range switch S is further rotated clockwise to the measured variable C, so the locking guide SK would adjust accordingly, and share the input terminal 2c. The recess 3 is formed as an elongated hole, so that the resulting in rotating the locking guide SK offset from the arrayed on a straight line input terminals 2a to 2c balanced. If one arranges the input terminals 2a to 2c so on, that they lie on a circular arc to the bearing point of the locking guide SK, so sufficient a circular recess of sufficient diameter.

The bearing of the locking guide SK is done by a trained on the inside of the top wall 21a of bearing pin 24 which engages in a bearing hole 33 of the locking guide SK. Likewise mounted in the top wall 21a, but placed from the outside, the actuating part is 5. Starting from the plane in which the coupling elements 5c, 25 lie, the locking guide SK extends to a lock plate 26, in which the recess 3 is located, so that they can slide over the designed as sockets 4 input terminals 2a, 2b, 2c, and only a particular receiving channel 4a releases. For the housing inner side, the locking guide nor the recess is protected 22 cover covering 27th The recess 22 is sized to the size and angle of rotation of the locking guide SK.

As shown in FIGS. 7 to 9 reveal, there are a variety of possible solutions, such as coupled to the measurement range switch S locking guide SK, certain input terminals 2a to 2c lock or unlock against a contacting connecting leads. So 7 is shown in Fig., The locking guide SK constructed using three gate valves SS1 to SS3, each of which is held by a spring FE in a blocking position, from which it can be NS only by a cam slide displaced, and then into a release position arrives. In this example, the cam slider ensures NS sure that the locking slide SS2 with its recess 3 releases the input terminal 2b. This input terminal 2b is associated with the set on the measurement range switch S B measured variable.

The operation of the locking guide according to Fig. 8 corresponds to that of Fig. 7, the cam slider NS is only driven by a translating device, constructed as a slide switch and the measurement range switch S not by a rotatable measurement range as shown in Fig. 7 P.

Fig. 9 shows that the associated with the measurement range switch S actuating member may not necessarily be on the operating surface, but of course also attached to one of the side surfaces of the measuring instrument housing. In this example, a locking detent particularly simple type is used because its straight displacement corresponds directly to the linear arrangement of the input terminals 2a to 2c.

Figs. 10 and 11 indicate that the blocking of certain input terminals 2a, 2b is also possible with the aid of an electromagnetically actuated locking bar R. Fig. 10 allows the coupling of the measurement range switch S with two auxiliary circuits H1 to detect H2, in each of which a solenoid actuator M1, M2 is disposed, which each have a catch R1, R2 from the corresponding input terminals 2a, 2b with respect to the contacting connecting a measuring line L2 with can lock the connector ST2. In the present example of the measurement range switch S is provided with an additional switching path S1 which activates according to the predetermined by the measurement range S selection of measuring B, which is also assigned to the input terminal 2a, connecting the auxiliary circuit H1 to a voltage source U and thus the magnetic plates M1 , in turn, with the safety catch R1 to the input terminal 2a is blocked. On the basis of the measurement object Q represented as a voltage source can thus provided with the connectors ST1, ST2 measuring lines L1, L2 only the common input terminal 1 and the measured quantity of B1 associated input terminal 2b contact and thus close the input circuit b. About one connected to the measurement range switch S Meßbereichsnetzwerk N, which must depend on the nature and structure according to the respective measured value, the test signal arrives at the actual measuring system Z, which provides for the evaluation and display of the measured signal. After switching the measurement range switch S to the measurable variable A of the magnet plate would M1 the associated catch R1 retreat back into the starting position, thus releasing the input terminal for the process variable A, while the second magnetic positioner M2 would now ativiert and the second locking bolt R2 the input terminal 2b would terminate.

Fig. 11 is the formed as a socket 4 input terminals 2a, 2b illustrate with the driven locking bolt by a magnetic plate M R, which closes the receiving channel 4a of the receptacle 4 relative to a contact.