JP2010033119A - Analog output device with self-diagnostic function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analog output device capable of highly accurately detecting its own abnormality. <P>SOLUTION: The analog output device includes: an output unit 1 that is provided with a first output circuit 11 and a second output circuit 12, and combines and outputs an output of the first output circuit 11 and an output of the second output circuit 12; a first detection means 21 that detects an output state of the first output circuit 11; a second detection means 22 that detects an output state of the second output circuit 12; and a determination means 3 that performs self-diagnostic determination based on detection results of the first detection means 21 and second detection means 22. The determination means 3 separately determines respective abnormalities of the first output circuit 11 and the second output circuit 12 based on a detection value of the first detection means 21 and a detection value of the second detection means 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an analog output device having a self-diagnosis function.

As a current output module used in the field of process automation, a current output module having a source / sink function capable of outputting both a positive current and a negative current is used. A bipolar output current can be obtained by adding the source current and the sink current, and this output current is given to an external device such as a plant control device. In addition, the current output module is provided with a self-diagnosis function for detecting an abnormality of the module by reading back the output current.
JP 2008-107224 A

  However, since an abnormality does not appear in the output current depending on the failure mode of the current output module, the module abnormality may not be detected by the conventional self-diagnosis function. For example, even if both the source current and the sink current are abnormal, if no abnormality appears in the added output current value, the module abnormality cannot be detected.

  An object of the present invention is to provide an analog output device capable of detecting a self abnormality with high accuracy.

An analog output device according to the present invention is an analog output device having a self-diagnosis function, and includes a first output circuit and a second output circuit, and the output of the first output circuit and the second output circuit. An output unit that synthesizes and outputs the output, a first detection unit that detects an output state of the first output circuit, a second detection unit that detects an output state of the second output circuit, Determination means for making a determination on self-diagnosis based on the detection results of the first detection means and the second detection means.
According to this analog output device, since the output state of the first output circuit and the output state of the second output circuit are detected independently, the state of the output unit can be detected with high accuracy.
The first detection means detects an output value of the first output circuit, the second detection means detects an output value of the second output circuit, and the determination means is based on these output values. A determination may be made.
The determination unit may perform determination based on a sum of the output value detected by the first detection unit and the output value detected by the second detection unit.
The first output circuit may output a source current, the second output circuit may output a sink current, and the output unit may output an output current obtained by combining the source current and the sink current.

  According to the analog output device of the present invention, since the output state of the first output circuit and the output state of the second output circuit are detected independently, the state of the output unit can be detected with high accuracy.

  Hereinafter, embodiments of an analog output device according to the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram illustrating a configuration of an analog output device according to an embodiment.

  As shown in FIG. 1, the analog output device of the present embodiment includes a first output circuit 11 and a second output circuit 12, and the output of the first output circuit 11 and the second output circuit 12. Output unit 1 that combines and outputs the output, first detection unit 21 that detects the output state of the first output circuit 11, and second detection unit that detects the output state of the second output circuit 12. 22 and determination means 3 for making a determination on self-diagnosis based on the detection results by the first detection means 21 and the second detection means 22.

  The first output circuit 11 and the second output circuit 12 are given a set value indicating the output voltage or the output current, and the first output circuit 11 and the second output circuit 12 correspond to this set value, respectively. Outputs the voltage or current corresponding to the attached output value. The outputs of the first output circuit 11 and the second output circuit 12 are combined and output from the output unit 1 as an output voltage or output current (actual output) indicated by the set value.

  FIG. 2 is a block diagram illustrating a configuration of the determination unit 3.

  As shown in FIG. 2, the determination unit 3 includes comparators 31 to 34 for performing determination, and an adder 35 that adds the detection value of the first detection unit 21 and the detection value of the second detection unit 22. Are provided.

  The comparator 31 compares the sum of the detection value of the first detection means 21 and the detection value of the second detection means 22 obtained by the adder 35 with the value indicated by the set value, and the sum of the detection values. And the set value are not within a certain range, it is determined that the actual output is abnormal. As described above, by using the sum of the detection values, it is possible to perform the same determination as the determination by reading back the actual output value.

  The comparator 32 compares the detection value of the first detection means 21 and the detection value of the second detection means 22 obtained by the adder 35 with the open detection threshold value, and the sum of the detection values is open. When the detection threshold is exceeded (to the open detection side), it is determined that the output end is in the open state. As described above, by using the sum of the detection values, it is possible to perform the same determination as the determination by reading back the actual output value.

  The comparator 33 compares the detection value of the first detection means 21 with the corresponding output value of the first output circuit 11 associated with the set value, and compares the detection value of the first detection means 21 with the above-mentioned correspondence. When the difference from the output value is not within a certain range, it is determined that the first output circuit 11 is abnormal. Thereby, abnormality of the 1st output circuit 11 can be judged independently.

  The comparator 34 compares the detection value of the second detection means 22 with the corresponding output value of the second output circuit 12 associated with the set value, and compares the detection value of the second detection means 22 with the above-mentioned correspondence. When the difference from the output value is not within a certain range, it is determined that the second output circuit 12 is abnormal. Thereby, the abnormality of the 2nd output circuit 12 can be determined independently.

  FIG. 3 shows the correspondence between the state of the output unit 1 and the determination result for Case 1 to Case 6.

  As shown in FIG. 3, in case 3 to case 5, an abnormality has occurred in the first output circuit 11 or the second output circuit 12. However, the actual output (actual output) indicates normality, and the determination by the comparator 31 also indicates normality. In the analog output device of this embodiment, even when the actual output is normal, when the internal output circuit is abnormal, the comparator 33 or the comparator 34 can detect the abnormality. Therefore, a conclusion that there is an abnormality in the output circuit can be obtained as a final determination result in these cases.

  Hereinafter, the configuration of the output unit in the analog output device of the present invention will be described.

  FIG. 4A is a block diagram illustrating a configuration example of the output unit.

  As shown in FIG. 4A, the output unit 1 outputs a set value indicating the current value of the output current, receives the set value from the control circuit 13, and associates it with the set value. And a second output circuit 12 that receives the set value from the control circuit 13 and outputs a sink current associated with the set value.

  FIG. 4B is a block diagram showing the configuration of the first output circuit 11 that is a source current output circuit and the second output circuit 12 that is a sink current output circuit.

  As shown in FIG. 4B, the first output circuit 11 includes a level conversion circuit 11a for level-shifting the set value (voltage value) from the control circuit 13, and an output value (voltage value) of the level conversion circuit 11a. ) To a current value. The second output circuit 12 includes a level conversion circuit 12a for level shifting the set value (voltage value) from the control circuit 13, and a voltage for converting the output value (voltage value) of the level conversion circuit 12a into a current value. / Current conversion circuit 12b.

  FIG. 5 is a diagram illustrating a circuit configuration example of the output unit 1.

  In the example of FIG. 5, an operational amplifier 51, an n-type FET 52, a resistor 53a having a resistance value R1, a resistor 53b having a resistance value R1, a resistor 54a having a resistance value R2, and a resistor 54b are used to form an inverting buffer. Level conversion circuits 11a and 12a are formed by the amplifier 55 and the voltage source 56 for level shift. The operational amplifier 57 constituting the non-inverting buffer, the p-type FET 58 as the source current output element, and the resistor 59 having the resistance value R3 constitute the current / voltage conversion circuit 11b. The operational amplifier 60 constituting the non-inverting buffer, the n-type FET 61 as a sink current output element, and the resistor 62 having a resistance value R3 constitute a current / voltage conversion circuit 12b.

  The actual output current applied to the load 4 is a current obtained by combining the source current of the current / voltage conversion circuit 11b and the sink current of the current / voltage conversion circuit 12b.

  The capacitors in each part of the circuit are used to adjust the response of the circuit, and the resistor connected to the gate of the FET is used to prevent parasitic oscillation.

  Next, the value of the source current output from the current / voltage conversion circuit 11 b is detected as a voltage generated in the resistor 59 by the first detection means 21. The value of the sink current output from the current / voltage conversion circuit 12 b is detected as a voltage generated in the resistor 62 by the second detection means 22. Thus, since the source current and the sink current are detected independently, the state of the output unit 1 can be accurately grasped as described above.

  FIG. 6A is a diagram showing a correspondence relationship between the set value and the output current (corresponding output value) in the circuit of FIG.

  As shown in FIG. 6A, the source current of the current / voltage conversion circuit 11b and the sink current of the current / voltage conversion circuit 12b are linear corresponding to the set value (voltage value: -15V to -12.5V). To change. In this example, the slopes of the source current and the sink current with respect to the set value are made equal. The actual output current given to the load 4 is a combination of the source current and the sink current, and the current value matches the set value.

  FIG. 6B is a diagram illustrating a correspondence relationship between the set value and the output current (corresponding output value) when a failure occurs. As shown in FIG. 6B, when the source current is offset to the plus side and the sink current is offset to the minus side with the same width, the source current is in a region where the set value is B or more, and the sink current is set to A. Each of the following areas is clamped. For this reason, when the set value exceeds the range of A to B, the actual output current given to the load 4 deviates from the set value. However, in the range where the set value is A to B, the actual output current shows a correct value (set value). In such a case, the analog output device according to the present embodiment detects the source current and the sink current independently, so that the offset of the current value can be detected even if the set value is in the range of A to B. Therefore, an internal abnormality can be detected quickly without waiting for an abnormality in the output current value that occurs when the set value exceeds the range of A to B.

  By the way, there may be a case where the analog output device is required to perform a fail-safe operation so that an abnormality in the analog output device does not affect the output external device. In such a case, the analog output device according to the present embodiment can determine an inherent abnormality in which no abnormality appears in the actual output. The effect can be prevented in advance. In addition, if the actual output is normal even if an inherent abnormality is found, there is no problem with the external device.In this case, for example, only the abnormality is notified and the output is continued without fail-safe operation. Is also possible.

  FIG. 7 shows the configuration of the output unit in which the output current is controlled by negative feedback. In the current output device 1 </ b> A of FIG. 7, the actual output current flowing through the load 4 is detected by the resistor 41, and the actual output current is feedback-controlled by negative feedback by the resistor 42 and the negative feedback loop 43. In this case, even if a failure occurs in the first output circuit 11 or the second output circuit 12, a desired actual output current may be forcibly obtained by feedback control. However, since the source current and the sink current are detected independently by the first detection means 21 and the second detection means 22, even if no abnormality is found in the actual output current, the first output circuit 11 Alternatively, the failure of the second output circuit 12 can be detected.

  In the above embodiment, the current output circuit is exemplified as the first output circuit and the second output circuit, but the present invention can also be applied to a voltage output circuit. In this case, the output unit is configured to output an output voltage obtained by adding the output voltage of the first output circuit and the output voltage of the second output circuit, and the output voltage of the first output circuit and the second output circuit The output voltage of the output circuit may be detected independently. Further, by detecting the sum of the output voltage of the first output circuit and the output voltage of the second output circuit, it is possible to make a determination instead of the determination based on the actual output voltage value.

  Further, as shown in FIG. 8, the present invention can also be applied to a case where three or more output circuits are provided in the output unit. In the example of FIG. 8, output circuits PS1, PS2,... PSn are provided in the output unit 1B, and outputs from these output circuits are combined and output. The detection circuits DT1, DT2,... DTn are associated with the output circuits PS1, PS2,... PSn, respectively, and the detection values of the detection means DT1, DT2,. With such a configuration, it is possible to detect each abnormality of the output circuits PS1, PS2,. Further, by determining the sum of the detection values of the detection means DT1, DT2,... DTn, it is possible to determine the actual output value and the output end opening.

  The analog output device according to the present invention is particularly effective for application to an IO module for a safety system (EN 61311-2) requiring high-precision diagnosis.

  The scope of application of the present invention is not limited to the above embodiment. The present invention can be widely applied to an analog output device having a self-diagnosis function.

The block diagram which shows the structure of the analog output device of one Embodiment. The block diagram which shows the structure of a determination means. The figure which shows the correspondence of the state of an output part, and a determination result. It is a figure which shows the structural example of an output part, (a) is a block diagram which shows the structural example of an output part, (b) is the 1st output circuit which is a source current output circuit, and the 2nd which is a sink current output circuit The block diagram which shows the structure of an output circuit. The figure which shows the circuit structural example of an output part. It is a figure which shows the correspondence of a setting value and output current (corresponding output value), (a) is a figure which shows the correspondence at the time of normal, (b) is a figure which illustrates the correspondence at the time of failure occurrence. The figure which shows the structure of the output part which controlled the output current by the negative feedback. The block diagram which shows the structure of the output part which provided the 3 or more output circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Output part 3 Determination means 11 1st output circuit 12 2nd output circuit 21 1st detection means 22 2nd detection means

Claims (4)

In analog output device with self-diagnosis function,
An output unit comprising a first output circuit and a second output circuit, and combining and outputting the output of the first output circuit and the output of the second output circuit;
First detection means for detecting an output state of the first output circuit;
Second detection means for detecting an output state of the second output circuit;
Determination means for making a determination about self-diagnosis based on the detection results by the first detection means and the second detection means;
An analog output device comprising: The first detection means detects an output value of the first output circuit, the second detection means detects an output value of the second output circuit, and the determination means is based on these output values. The analog output device according to claim 1, wherein the determination is performed. The determination unit performs determination based on a sum of the output value detected by the first detection unit and the output value detected by the second detection unit. 2. The analog output device according to 2. The first output circuit outputs a source current, the second output circuit outputs a sink current, and the output unit outputs an output current obtained by combining the source current and the sink current. The analog output device according to any one of claims 1 to 3.

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