Field device for determining or monitoring a process variable in automation technology

1. A field device for determining or monitoring a process variable in automation technology, wherein the field device meets a safety standard, which is required in a predetermined safety-critical application, comprising:

a sensor, which works according to a defined measuring principle;

a control/evaluation unit, which processes and evaluates measurement data delivered by said sensor along at least three redundantly and/or diversely designed measuring channels; and

a voter which is associated with said control/evaluation unit and which is composed of a plurality of components, which are at least partially double redundantly designed and which is embodied as a majority voter and has three components: a comparator stage, which compares output signals delivered by said individual measuring channels with one another, a failure recognition stage, which by correlating the output signals of said comparator stage detects a failure occurring in a measuring channel of said individual measuring channels, and an output selection stage, wherein

said output selection stage has a multiplexer, which is so embodied that it makes a selection between the output signals of said measuring channels and an alarm signal, as a function of the output signals of said failure recognition stage.

2. The field device as claimed in claim 1 , wherein:

said voter is composed of a plurality of voter channels, wherein each voter channel includes a part of said comparator stage and a part of said failure recognition stage; and

each voter channel is embodied as an integrated component of an associated measuring channel.

3. The field device as claimed in claim 2 , wherein:

said comparator stage includes in each voter channel two redundant comparators, which compare an output signal of a selected measuring channel, in each case, with an output signal of remaining measuring channels, so that output signals of the three measuring channels are doubly compared by said two redundant comparators.

4. The field device as claimed in claim 3 , wherein:

said failure recognition stage is a logic stage, which is constructed of logic gates.

5. The field device as claimed in claim 4 , wherein:

each logic stage is composed of two AND gates and an OR gate;

connected to inputs of a first AND gate are output signals of two redundant comparators of a first voter channel associated with the selected measuring channel;

connected to a second AND gate are output signals of said two redundant comparators of a second voter channel and of a third voter channel redundant to the inputs of said first AND gate; and

the output signals of said first AND gate and of said second AND gate form input signals of said following OR gate.

6. The field device as claimed in claim 3 , wherein:

said output selection stage is so embodied that it either selects a measuring channel, when no failure or a failure in one of the three measuring channels or in one of said voter channels occurs, or that it generates a failure report, when at least two failures occur in at least two measuring channels and/or two voter channels.

7. The field device as claimed in claim 2 , wherein:

said control/evaluation unit with said measuring channels and/or associated components of said voter, respectively said voter channels, is embodied in said measuring channels at least partially as a reconfigurable logic chip (FPGA) with a plurality of partially dynamically reconfigurable function modules.

8. The field device as claimed in claim 7 , wherein:

said control/evaluation unit so configures the partially dynamically reconfigurable function modules in said measuring channels as a function of the respectively defined safety-critical application that the field device meets the required safety standard.

9. The field device as claimed in claim 7 , wherein:

there is associated with said control/evaluation unit at least one microprocessor, which partially dynamically reconfigures the partially dynamically reconfigurable function modules of a measuring channel of said diversely designed measuring channels and/or a voter channel of said voter, in which a failure has been detected.

10. The field device as claimed in claim 9 , wherein:

said at least one microprocessor is configured permanently in a static region of the logic chip (FPGA).

11. The field device as claimed in claim 1 , wherein:

each measuring channel has its own voltage supply.

12. The field device as claimed in claim 1 , wherein:

at least one of the three measuring channels is configured analog-based in an FPAA.

13. The field device as claimed in claim 1 , wherein:

the individual measuring channels are so spaced from one another that a temperature and/or voltage change in a measuring channel have/has no influence on a neighboring measuring channel.