Safety circuit and method for testing a safety circuit in an automation system

Abstract

A safety circuit for the multi-channel processing of an input signal. The safety circuit includes an analog-to-digital conversion device having a first analog input and a second analog input and at least one digital output for processing the input signal. Furthermore, the safety circuit has a test device which is set up to apply a test signal at the first and/or second input of the A/D conversion device in such a way that the test signal superposes the input signal such that the test signal dominates the input signal.

Claims

1. A safety circuit, comprising: an input circuit adapted to input a first input signal and a second input signal and provide the first input signal and the second input signal at an output; an A/D converter having a first analog input and a second analog input and a digital output; a first signal line connected to the output of the input circuit and to the first analog input of the A/D converter to relay the first input signal, from the input circuit, in analog form, wherein the A/D converter device is configured to convert the first input signal in analog form at the first analog input to a first input signal in digital form and to output the first input signal in digital form at the digital output; a second signal line connected to the output of the input circuit and to the second analog input of the A/D converter to relay the second input signal, from the input circuit, in analog form, wherein the A/D converter is arranged to convert the second input signal in analog form at the second analog input to a second input signal in digital form and to output the second input signal in digital form at the digital output; a control and evaluation device for evaluating the first input signal in digital form and the second input signal in digital form, wherein the digital output of the A/D converter is connected to at least one input of the control and evaluation device; and a test device to output an analog test signal, wherein the test device has a control input which is connected to a control output of the control and evaluation device and wherein the control and evaluation device is further configured to control the test device, wherein the test device has a first analog test output to output the analog test signal, the first analog test output being connected to the first signal line and the test device has a second analog test output to output the analog test signal, the second analog test output being connected to the second signal line.

2. The safety circuit according to claim 1, wherein the test device has a test input for the input of the analog test signal, wherein at least during a test period, the analog test signal is applied, wherein a signal source is connected to the test input and wherein the signal source is adapted to generate the analog test signal via a voltage or current source.

3. The safety circuit according to claim 1, wherein the analog test signal is a ground potential or a constant voltage potential or a variable voltage potential.

4. The safety circuit according to claim 1, wherein the analog test signal is a constant or a variable current.

5. The safety circuit according to claim 1, wherein the analog test signal follows a predetermined or predeterminable signal path during the test period.

6. The safety circuit according to claim 1, wherein the test device has a switching device, wherein the switching device is set up to switch the analog test signal to the first analog test output and/or to the second analog test output.

7. The safety circuit according to claim 6, wherein the switching device has at least two switches, wherein the switches are controlled individually and/or in groups.

8. The safety circuit according to claim 1, wherein the first signal line comprises a first damping element so that the input circuit with an interposition of the first damping element is connected to the first analog input of the A/D converter, and wherein the second signal line comprises a second damping element so that the input circuit with an interposition of the second damping element is connected to the second analog input of the A/D converter.

9. The safety circuit according to claim 8, wherein the first damping element, the second damping element and an output impedance of the test device and/or the signal source are configured such that the first input signal in analog form and the analog test signal are superposed during the test period at the first analog input of the A/D conversion device and/or wherein the second input signal in analog form and the analog test signal during the test period are superposed at the second analog input of the A/D conversion device such that the analog test signal dominates the first input signal in analog form or the second input signal in analog form.

10. The safety circuit according to claim 1, wherein the control and evaluation device has a processor for processing the first input signal in digital form and/or the second input signal in digital form.

11. The safety circuit according to claim 1, wherein the A/D converter comprises a first A/D converter and a second A/D converter, wherein the first A/D converter is configured to convert the first input signal in analog form to the first input signal in digital form and to output it at the digital output and wherein the second A/D converter is configured to convert the second input signal in analog form to the second input signal in digital form and to output it at the digital output.

12. The safety circuit according to claim 1, wherein the test device further comprises: a multiplexer having a controllable logic; and a switching device having a plurality of switches configured to be independently switched.

13. The safety circuit according to claim 1, wherein the test device is configured to output a continuous analog signal as the analog test signal.

14. A method for testing a safety circuit, the method comprising: providing a signal source for generating an analog test signal; and outputting the analog test signal, from a test device to a first and/or a second signal line, connecting, during a test period, the analog test signal applied to a test input of the test device via a switching device, replacing the analog test signal with a first input signal in analog form at the first analog input of an A/D converter and/or replacing the analog test signal with a second input signal in analog form at the second analog input of the A/D converter.

15. The method according to claim 14, wherein, during the test period, via the test device the first input signal in analog form is superposed with the analog test signal such that the analog test signal dominates at the first analog input of the A/D converter and/or wherein the second input signal in analog form is superposed with the analog test signal such that the analog test signal dominates at the second analog input of the A/D converter.

16. The method according to claim 14, wherein the analog test signal is changed by automatically following a predetermined or predeterminable signal path.

17. The method according to claim 14, wherein a control and evaluation device, during the test period checks the analog test signal output by the test device at the first analog input of the A/D converter and/or at the second analog input of the A/D converter for against an expected value and triggers an error signal of an event of a disparity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 is a block diagram of a safety circuit of an exemplary embodiment comprising an input circuit, a test device, an A/D conversion device and a control and evaluation unit,

(3) FIG. 2 is a block diagram of a safety circuit of an exemplary embodiment having, by way of example, three sensor signals, a test device, an A/D conversion device and a control and evaluation unit,

(4) FIG. 3 is a block diagram of a test device having a signal source, and

(5) FIG. 4A and FIG. 4B illustrate an exemplary signal path of the test signal and the input signal in analog form.

DETAILED DESCRIPTION

(6) FIG. 1 shows a block diagram of a security circuit 1 of an exemplary embodiment. The safety circuit 1 includes an input circuit 500 for connecting an analog sensor. The input circuit has a matching circuit for outputting a sensor signal S.sub.E at the output 501. A first signal line 410 is connected to the output 501 of the input circuit 500 and to the first analog input 101 of the A/D conversion device 100. Further, a second signal line 420 is connected to the output 501 of the input circuit 500 and to the second analog input 102 of the A/D conversion device 100.

(7) In the first signal line 410, the damping element Z.sub.1 is connected in series, so that the sensor signal S.sub.E output from the input circuit 500 at the output 501 is damped.

(8) Further, in the second signal line 420, the damping element Z.sub.2 is connected in series, so that the sensor signal S.sub.E output from the input circuit 500 at the output 501 is also dampened.

(9) The damping elements Z.sub.1, Z.sub.2 and the damping factors derived therefrom are co-determined by their impedances. The first and second input signals in analog form S.sub.EA1 and S.sub.EA2 dampened by means of the damping elements Z.sub.1 and Z.sub.2 are processed in the A/D conversion device 100.

(10) The A/D conversion device 100 as shown in the embodiment of FIG. 1 formed of two A/D converters known from the prior art. The A/D converters 150 and 160 convert the first and second input signals in analog form S.sub.EA1 and S.sub.EA2, present at the first and second analog inputs 101 and 102, to first and second input signals in digital form S.sub.1D and S.sub.2D and output these via a first and a second digital output 109 and 110.

(11) For further processing of the first and second input signals in digital form S.sub.1D and S.sub.2D, the signals are relayed via data lines 430 and 440 to a first and a second input 601 and 602 of the control and evaluation device 600.

(12) The control and evaluation device 600 formed of two microcontrollers μC1 and μC2, each of which is connected with one another and with the inputs 601 and 602 for data processing. The microcontrollers are configured to process the first and second input signals in digital form S.sub.1D and S.sub.2D, wherein the processing may include an evaluation and/or a relaying, for example, to a higher level controller.

(13) As shown in the exemplary embodiment in FIG. 1, the safety circuit 1 has a test device 300, wherein the first analog test output 310 of the test device 300, the first analog input 101 of the A/D conversion device 100 are electrically connected to the damping element Z.sub.1 at the node 411. Furthermore, the second analog test output 320 and the second analog input 102 of the A/D conversion device 100 are electrically connected to the damping element Z.sub.2 at the node 421.

(14) The test device 300 further comprises a test input 302 for inputting an analog test signal S.sub.TA. A signal source 700 coupled to the test input 302 serves to generate the analog test signal. The signal source is connected via a control line to the control output 610 of the control and evaluation unit 600 and is configured to set the analog test signal S.sub.TA according to a specification given by the control and evaluation device 600.

(15) To control the test device 300, the control input 301 is connected to the control and evaluation device 600. In addition, the test device is set up to switch the analog test signal S.sub.TA to the first analog test output 310 and/or to the second analog test output 320 according to a specification given by the control and evaluation unit 600.

(16) The test device is structured in a simple manner (see the exemplary embodiment of FIG. 3) and has a switching logic 360 and a switching device 350 with a number of switches 355, which are controlled by the switching logic and which connect the analog test signal S.sub.TA with the analog test outputs according to the specifications of the control and evaluation logic. The low output impedance of the first analog test output 310 and/or the second analog test output 320, as shown in the exemplary embodiment, causes a much larger signal amplitude of the test signal S.sub.TA than the signal amplitude of the input signal (S.sub.EA1/S.sub.EA2) such that the analog test signals S.sub.TA dominate at the first analog input 101 and/or at the second analog input 102 of the A/D conversion device 100.

(17) With the exemplary embodiment of FIG. 1, a safety circuit is realized in which the signal path can be simply tested, for example, for line breakage, since both the first input signal in analog form S.sub.EA1 and the analog test signal S.sub.TA are guided over a common signal path and are evaluated. Advantageously, the analog signals are subject to the same physical properties. Furthermore, it is possible to test the A/D conversion device 100, in particular the A/D converters (150, 160).

(18) FIG. 2 shows a block diagram of the safety circuit 1 of a further exemplary embodiment with for reasons of clarity, for example, 3 input circuits (500, 500′, 500″) for the independent processing of 3 sensor signals (S.sub.E, S.sub.E′, S.sub.E″).

(19) The A/D conversion device 100 is configured to process a corresponding number of first and second input signals in analog form (S.sub.EA1, S.sub.EA2, S.sub.EA1′, S.sub.EA2′, S.sub.EA1″, S.sub.EA2″).

(20) The A/D conversion device 100, designed for example as a microchip, can include an integrated multiplexer and an A/D converter. The integrated multiplexer can be controlled by one of the microcontrollers μC1 or μC2 and relays the input signal present on the signal lines in analog form S.sub.EA1,2 and/or the analog test signal S.sub.TA to the A/D converter for converting the analog signals (S.sub.EA1,2/S.sub.TA) to input signals in digital form. In addition to testing the correct operation of the A/D converter, it is possible to test the integrated multiplexer, for example, for a short circuit. This is possible because both the input signals of analog type and the analog test signals are routed via the same signal path.

(21) The number of the sensor signals to be processed depends on the number of first and second analog test outputs of the test device 300 (see exemplary embodiment of FIG. 3) and on the number of first and second analog inputs of the A/D conversion device 100.

(22) At the digital output 109 of the A/D conversion device 100, the data is for example made available to the control and evaluation device via an SPI interface (serial peripheral interface). In this case, the data line is (430) suitable for passing the data flow to an input (601) of the control and evaluation device. Thus, the circuit structure as described in the exemplary embodiment of FIG. 2 can produce a test circuit, which can be easily adapted to any number of sensor inputs.

(23) FIG. 3 shows a block diagram of a test device 300 of another exemplary embodiment, designed for example, for 6 sensors. The test device 300 includes a switching device 350 with 12 switches 355, which are independently and individually switchable by a switching logic 360 and can create a conductive connection between the test input 302 and the corresponding first and/or second analog test outputs (310, 320). The switching logic 360 is controlled by a control and evaluation device via the control input 301. The switches 355 are preferably designed as an integrated semiconductor circuit. The test device from FIG. 3 can be realized, for example, by a 6-channel CMOS analog multiplexer. Furthermore, the test device 300 comprises a test input 302 for inputting an analog test signal S.sub.TA. The analog test signal S.sub.TA is generated by a signal source 700.

(24) In the exemplary embodiment of FIG. 3, the signal source 700 is formed as an external component and also has a control input 701. Alternatively, the signal source 700 can be integrated in the test device 300 and be controlled via a switching logic 360. The signal source 700 may be a signal generator or a simple current/voltage source that outputs a constant or variable analog signal. Further, a simple transistor connected to ground is conceivable as the signal source 700. Preferably, the signal source 700 has a voltage or current source which can be set externally, for example, by a processor of a control and evaluation circuit 600 or is designed as such a source. For example, the signal source 700 has a digital-to-analog converter for generating the test signal.

(25) FIG. 4A shows, for example, a voltage curve (U [V]) at a first or second input 101, 102 of an A/D conversion device 100 as a function of time t, wherein S.sub.EA corresponds to an input signal in analog form and S.sub.TA corresponds to an analog test signal.

(26) At a time t=0, a first input signal dominates in analog form S.sub.EA, for example, at the first analog input 101 of the A/D conversion device 100. At time t=t.sub.1, the analog test signal S.sub.TA is applied via the first analog output 310 of the test device 300 to the first analog input 101 of the A/D conversion device 100 and superposes the input signal in analog form S.sub.EA up to the time t=t.sub.2. The analog test signal can be constant (S.sub.TA=const.) or variable. Preferably, the analog test signal traverses the entire measurement range of the A/D converter to determine correct operation.

(27) FIG. 4B shows a further example of a voltage curve at an input of an A/D conversion device, wherein two tests (T.sub.test1, T.sub.test2) are performed in rapid succession. For example, a first test during a first test period T.sub.test1 downstream of a voltage of an input signal in analog form with a test signal S.sub.TA1 and a second test during a second test period T.sub.test2 upstream of the voltage of the input signal in analog form with a test signal S.sub.TA2. Here, the duration of a test can be shortened because it is not necessary to pass through the entire measurement range, but only through individual sections of the measurement range in short time intervals.

(28) The safety circuit 1 of the exemplary embodiment of FIG. 1 preferably has at least two operating modes. A first operating mode is normal operation, i.e., the analog signals made available by a sensor are processed in the input circuit 500, provided at the output 501 of the input circuit and relayed via multiple channels, in the present case via two channels, via two signal lines 410 and 420 to the A/D conversion device 100. The A/D conversion device 100 generates corresponding first or second input signals in digital form S.sub.1D, S.sub.2D from the processed first or second input signals in analog form S.sub.EA1, S.sub.EA2.

(29) The first or second data in digital form S.sub.1D, S.sub.2D are transmitted via the data line(s) 430, 440 with, for example, a serial bus to the control and evaluation device 600 and are processed with the aid of programs on a processor or by means of the first microcontroller μC1 and/or the second microcontroller μC2. In this case, processing includes, for example, a comparison, which data communicated via the data lines 430 and 440 and/or are compared to their relay, for example, to a superordinate controller (PLC).

(30) A second operating mode is the test operation. In this operating mode, by means of the test device 300 each signal path 410, 420 can be tested for line breakage as well as the transfer characteristic or function of the A/D converter. In addition, it is also possible to check the first and/or second input signal in digital form S.sub.1D, S.sub.2D output by the A/D conversion device 100 against an expected value. Advantageously, the expected value is predetermined by the control and evaluation device 600.

(31) In test mode, a test routine is executed in the form of a program, preferably in the control and evaluation device 600. The test routine can be initiated manually by a user and/or cyclically by the control and evaluation device 600 or by a higher level controller (PLC) and contains a sequence of instructions for controlling parts of the safety circuit, particularly the signal source 700 of the test device 300.

(32) The signal source 700 is driven, for example, by a processor or preferably by one of the microcontrollers μC1 or μC2 for outputting a defined analog test signal S.sub.TA. This test signal S.sub.TA may be a ground potential, a voltage potential, a (temporally) variable voltage potential or a current or variable current (FIG. 4).

(33) The test device 300 according to the exemplary embodiment of FIG. 3, driven by the evaluation and control device 600, controls the switches 355 with the switching logic 360 such that the first signal line 410 is connected via one of the first analog test outputs, for example 310a of the test device 300, with the analog input 302 of the test device 300. The analog test signal S.sub.TA superposes the first input signal in analog form S.sub.EA1 on the signal line 410 and dominates the first input signal in analog form S.sub.EA1 at the analog input 101 of the A/D conversion device 100, while the first input signal in analog form S.sub.EA1 is damped by the damping element Z1.

(34) In the simplest case, the amplitude of the first input signal in analog form is changed, in particular reduced, during damping.

(35) The A/D conversion device 100 in the exemplary embodiment of FIG. 1 converts the analog test signal S.sub.TA, for example, to a first input signal in digital form S.sub.1D. The evaluation and control unit 600 checks the first input signal in digital form S.sub.1D against an expected value that corresponds to the digitized analog test signal S.sub.TA. If the values match, it can be assumed that the analog-to-digital conversion in the A/D conversion device 100, the corresponding signal and data lines, and the data interface are without errors.

(36) This test can also be performed for the second signal line 420. Advantageously, the tests can be performed in a time sequence, for example, one after the other, so that the signals S.sub.E output by the sensor can continue to be processed by the control and evaluation unit 600 without an interruption of the running process.

(37) FIG. 4 shows a diagram with a signal path in dependence on time that, for example, is present at the first analog input (101) of the A/D conversion device (100).

(38) The input signal in analog form S.sub.EA is superposed by the analog test signal S.sub.TA at time t.sub.1, the start of the test period Tt.sub.est, wherein the analog test signal S.sub.TA in its simplest embodiment satisfies the following condition S.sub.TA>0 and S.sub.TA>S.sub.EA. The test period is defined by the time interval Tt.sub.est=t.sub.2−t.sub.1. The analog test signal S.sub.TA may be a time-constant signal, for example a voltage potential, a ground potential (S.sub.TA=0) or else a constant current signal. However, it is also conceivable that the analog test signal S.sub.TA is a variable voltage potential or a variable current, wherein variable in this context may be, for example, a course of the analog test signal that is temporally altered over the test period T.sub.test. It is particularly advantageous that in this test, the entire value range of the A/D conversion device is run through and thus can be tested.

(39) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.