JP2002043943A - Analog output device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an analog output device that can simply diagnose itself with high reliability at a low cost even when the circuit is in operation. SOLUTION: A channel in which a digital/analog converter 21 is provided is referred to as a channel ch1 and a channel in which a digital/analog converter 22 is provided is referred to as a channel ch2. When a CPU instructs diagnosis of a prescribed channel (the ch1 is selected), the other channel not being a diagnosis object is a comparison channel (the ch2 is selected). A digital signal with the same value as that of the diagnosis object channel is given to the digital/analog converter 22 of the comparison channel, a comparator circuit 51 compares an output of the digital/analog converter 22 with an output of an output buffer 31 in the diagnosis object channel to discriminate that there is a fault in the diagnosis object channel when they have a prescribed difference level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog output device having an operation diagnostic function in an analog output circuit for converting a digital signal used for a program controller or the like into an analog signal.

[0002]

2. Description of the Related Art Conventionally, a program controller is used for various devices, and for example, a configuration as shown in FIG. 8 is known.

The analog output device is a CP (not shown).
It has an input buffer 110 for receiving a signal from U, a D / A converter 120 for converting a digital signal to an analog signal, an output buffer 130 for stably outputting the output of the D / A converter 120 to the outside, and the like. are doing.

The analog output device is often provided with multiple channels so that a plurality of signals can be processed. In FIG. 8, a D / A converter 1 for channel 1 (ch1) is used.
21 and an output buffer 131, and a two-channel D / A converter 122 and an output buffer 132 for channel 2 (ch2).

[0005] The digital signal input from the CPU to the input buffer 110 is input to the D / A converter 120 of the corresponding channel, converted into an analog signal, and output from the output buffer 130.

At this time, the D / A converter 130 to be used is selected by designating a channel (designating an address) from the CPU.

It is very important to properly grasp whether or not such an analog output device is operating normally in a field where the reliability of equipment is strictly required, such as a nuclear power plant. .

[0008]

However, as described above, the analog output device does not have a self-diagnosis function for judging whether or not the device is operating normally. Or an analog input circuit to monitor the output status and compare the output value and the input value with the host computer for diagnosis. It is necessary to perform circuit diagnosis by comparing with an output value, and the following problems have been pointed out.

That is, when an external digital input circuit or an analog input circuit is attached to monitor the output state or when an input function is attached to the output circuit, the amount of hardware increases and the device becomes expensive and the mounting becomes expensive. There is a problem that the area becomes large and the device becomes large, and there is a problem that the processing speed is reduced due to an increase in the amount of software.

Therefore, the present invention provides a highly reliable, inexpensive,
It is another object of the present invention to provide an analog output device capable of easily performing self-diagnosis.

[0011]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a D / A converter for converting at least a digital signal into an analog signal and an analog signal from the D / A converter. A plurality of channels each including an output buffer for stably outputting the data; and an input buffer for inputting a digital signal of a predetermined value to a D / A converter of a predetermined channel based on a signal from the control unit. In the analog output device having the analog output circuit, when the control unit instructs the diagnosis of the predetermined channel, one channel not to be diagnosed is set as a comparison channel, and the D / A converter of the comparison channel is used as a diagnosis target channel. And the output of the D / A converter in the comparison channel and the output of the output buffer in the channel to be diagnosed. And a diagnostic means for judging that there is an abnormality in the channel to be diagnosed when there is a predetermined difference between them, so that self-diagnosis can be performed with high reliability, at low cost, and easily. It is characterized by.

According to a second aspect of the present invention, two or more analog output circuits are provided, and when one is operating, the other is on standby to configure a redundant circuit, and when there is an abnormality in a channel to be diagnosed, diagnosis is performed. An operation switching means for setting an operating analog output circuit to a standby state by a signal output from the means and for setting the standby analog output circuit to an operating state, and automatically operating according to a diagnosis result; The circuit is switched.

[0013] According to a third aspect of the present invention, in the diagnostic device, the diagnostic means comprises:
Provided between the / A converter and the output buffer, even if the input value of the D / A converter is temporarily changed during diagnosis.
It has a CR filter that prevents the output of the output buffer in the channel from being affected, so that the diagnostic processing does not affect the operation state.

According to a fourth aspect of the present invention, there is provided a comparison circuit wherein the diagnosis means compares the output of the output buffer in the diagnosis channel with the output of the D / A converter in the comparison channel, and can hold the output. The diagnostic processing is characterized in that it does not affect the operation state.

According to a fifth aspect of the present invention, the diagnostic means includes: a diagnostic D / A converter to which a digital signal having the same value as the value input to the D / A converter of the diagnostic channel is input at the time of diagnosis; Output selecting means for selecting and outputting the analog signal from the D / A converter of the diagnostic channel among the analog signals from the D / A converter of each channel, and the signal from the output selecting means and the diagnostic D / A Compare with the signal from the converter,
And a comparison circuit capable of holding the output.
It is characterized in that the diagnostic processing does not affect the operation state.

The invention according to claim 6 is characterized in that a notifying means such as an LED for notifying the output state of the comparison circuit is provided so that the diagnosis result can be easily understood.

According to a seventh aspect of the present invention, an output of a comparison circuit in a plurality of channels is inputted, and when at least one of these channels is abnormal, an OR buffer or the like for outputting a signal indicating the abnormality is provided. It is characterized in that a judgment means is provided so that the presence or absence of an abnormality can be easily recognized.

According to an eighth aspect of the present invention, the judging means has a counting means for counting a diagnosis result when a plurality of diagnoses are performed intermittently, thereby preventing erroneous diagnosis due to a transient cause. It is characterized by doing.

A ninth aspect of the present invention is characterized in that a comparison reference setting device for setting a comparison reference in the comparison circuit is provided so that differences in circuit characteristics and the like can be adjusted.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an analog output device having an analog output circuit in a programmable controller having a self-diagnosis device according to the present invention.

An input buffer 10 to which a signal for designating a channel to be used (designating an address) is input from a CPU (not shown), a D / A converter 20 for converting a digital signal from the input buffer 10 into an analog signal, An output buffer 30 for holding a stable output, and C for delaying a signal input to the output buffer 30 by a predetermined time constant
The R filter circuit 40 includes a comparison circuit 50 that compares the output of the D / A converter 20 with the output of the output buffer 30 of another channel.

The CR filter circuit 40 and the comparison circuit 50 constitute a main part of the self-diagnosis function.

The analog output circuit has multiple channels so that a plurality of signals can be processed. FIG. 1 shows the case of two channels, and correspondingly, channel 1
D / A converter 21 and output buffer 31 for (ch1)
Are provided, and a D / A converter 22 for channel 2 (ch2) and an output buffer 32 are provided.

The CR filter circuit 40 and the comparison circuit 50 are also provided with a CR filter circuit 41 and a comparison circuit 51 for channel 1 (ch1) corresponding to the channel, and a CR filter circuit for channel 2 (ch2). 42 and a comparison circuit 52 are provided.

When self-diagnosis is performed in such a configuration, first, as shown in FIG. 2, the channel ch1 is designated, and the value of the channel ch2 is written to the channel ch1.

The output buffer 3 of the channel ch2
The output of the D / A converter 21 of the channel ch1 is compared with the output of the D / A converter 21 of the channel ch1, and the output is latched. I do.

At this time, when the difference between the value of the output buffer 32 and the value of the D / A converter 21 is large, the output of the comparison circuit 52 is set to, for example, a high level. Of course, it goes without saying that it may be set to a low level.

Next, the channel ch2 is designated, the value of the channel ch1 is written to the channel ch2, and the channel c
h1 output from the output buffer 31 and D /
The output of the A converter 22 is compared with the output of the comparison circuit 51, and the output is latched.

After performing the above processing, the comparison circuits 51 and 5
2 is read into the CPU to check the state of the analog output circuit.

At this time, when the output of the comparison circuit 51 is at a high level, it can be diagnosed that there is an abnormality in the channel ch2, and when the output of the comparison circuit 52 is at a high level, there is an abnormality in the channel ch1. Can be diagnosed.

The above diagnosis may be performed when the analog output circuit is actually used. In such a case, a signal set in the input buffer 10 for diagnosis is output from the output buffer 30. Therefore, there is a concern that various inconveniences may occur.

To prevent such inconvenience, a CR filter circuit 40 is provided for each channel.

That is, for example, when the value of the channel ch2 is set to the channel ch1 of the input buffer 10, the output from the D / A converter 21 becomes a value corresponding to the value of the channel ch2.

However, since the capacitor of the CR filter circuit 41 is charged with the value before the change of the set value, the time during which the set value is changed is sufficiently shorter than the time constant of the CR filter circuit 41. If there is, the input value of the output buffer 31 hardly changes, and therefore the output from the output buffer 31 hardly changes.

However, even if the set value is changed in such a short time, the time may be too short for the CPU to perform the diagnosis. Therefore, the output of the comparison circuit 50 is latched. I have.

As described above, even if the analog output circuit is in operation, diagnosis can be performed with a simple configuration without affecting the operation, and it is possible to secure low cost and high reliability. Become.

In the above description, the signal from the comparison circuit 50 is read into the CPU to diagnose whether or not each channel is abnormal. For example, as shown in FIG. Notification means 83 and 84 such as LED and buzzer
May be provided, and the output of the comparison circuit 50 may be input to the CPU together with the notification means 83 and 84.

By providing the notifying means 83 and 84 in this way, for example, when there is an abnormality in the channel ch1, the notifying means 83 is turned on, and the state of each channel can be easily checked.

In the case where it is sufficient to diagnose whether or not there is an abnormality in the analog output circuit, instead of individually diagnosing the presence or absence of an abnormality for a plurality of channels, for example, as shown in FIG. Alternatively, the output from the comparison circuit 50 may be input to the OR buffer 85, and diagnosis may be performed from the output.

By the way, it is supposed that noise enters from outside or the like during the diagnosis, resulting in erroneous diagnosis. As a method of avoiding such erroneous diagnosis, for example, it is preferable to diagnose the presence or absence of an abnormality by intermittently performing a diagnostic test a plurality of times and statistically evaluating the results.

In this case, for example, as shown in FIG. 5, the output from the comparison circuit 50 may be input to the OR buffer 85, and the output may be counted by the counter 86.

With this configuration, for example, diagnosis is performed five times, and even if an abnormality is detected once due to a transient factor such as noise, the number of times of abnormality detection is known, so that an appropriate judgment can be made. become.

In particular, such a configuration has an advantage that it is possible to determine (or estimate) a state in which an abnormality has begun to occur before the state becomes completely abnormal. That is,
For example, if the diagnosis is performed five times and the abnormality is detected three times, in such a case, it is difficult to imagine a transient cause such as noise, and it is suggested that some abnormality has begun to occur as the cause. You.

In a plant such as a nuclear power plant that requires extremely high reliability and cannot be easily stopped, the analog output device and the like are required to improve the reliability of the analog output device. A plurality of output circuits are provided and multiplexed. Normally, one analog circuit operates and the other analog circuit is in a standby state.

In such a case, as shown in FIG. 6, the standby analog output circuit can be operated based on the diagnosis result of the active analog output circuit.

That is, the analog output device shown in FIG. 6 basically shows a case where two analog output circuits having the configuration shown in FIG. 5 are provided for redundancy, and each analog output circuit has the same configuration as FIG. The output from the OR buffer 85 is input to the output selector 89.

As described above, when an abnormality is detected in one of the analog output circuits, the OR buffer 85 outputs a predetermined signal (for example, a high-level signal). Then, a signal is output from the standby analog output circuit assuming that an abnormality has occurred in the analog output circuit.

As described above, the switching to the standby analog output device is performed based on the diagnosis result without the intervention of the CPU or the like, so that the reliability is improved and the load on the CPU or the like can be reduced.

At this time, OR buffer 85 is generated due to noise or the like.
If an inconvenience such as a fluctuation in the output level occurs, a photo coupler (not shown) that is turned on in accordance with the output from the OR buffer 85 may be provided.

Next, a second embodiment of the present invention will be described with reference to the drawings. In the above embodiment, the CR filter circuit 40 is provided so that the diagnosis can be performed even while the analog output device is operating, and the output of the comparison circuit 50 can be latched.

On the other hand, in the present embodiment, a channel chx for diagnosis is provided as shown in FIG. 7 so that the influence of the diagnosis does not appear in the output buffer 30.

That is, the analog output device shown in FIG. 7 has an input buffer 1 to which a signal for designating a channel to be used (designating an address) is inputted from a CPU (not shown).
0, a D / A converter 20 for converting a digital signal from the input buffer 10 into an analog signal, an output buffer 30 for holding a stable output, and a D for diagnosis.
/ A converter 23, multiplexer 81 for selecting and outputting a signal from D / A converter 20, multiplexer 81
, And a signal from the diagnostic D / A converter 23.

The analog output device has a multi-channel structure so that a plurality of signals can be processed. FIG.
2 shows the case of two channels, and correspondingly, the D / A converter 21 for channel 1 (ch1) and the output buffer 3
1 and the D / A converter 22 for channel 2 (ch2) and the output buffer 32 are provided in the same manner as in the previous embodiment.

The D / A converter 23, the multiplexer 81 and the comparison circuit 82 constitute a diagnostic channel chx. Of course, as described above, the diagnostic channel ch
x does not interfere with other channels.

With the above configuration, when diagnosing the channel ch1, the D / A converter 23 for the channel c
The value of h1 is set, and the multiplexer 81 controls to select and output the signal from the D / A converter 21.

As a result, in the comparison circuit 82, the channel c
Signal from D / A converter 21 of h1 and diagnostic channel c
The signal from the hx D / A converter 23 is input, these values are compared, and the output is latched and read by the CPU.

As a result, if the difference between the signal from the D / A converter 23 for diagnosis and the signal from the D / A converter 21 of the channel ch1 to be diagnosed is large, the channel ch
Diagnose that 1 is abnormal.

The diagnosis is sequentially performed for the other channels by performing the above-described procedure.

Therefore, even when the analog output device is in operation, diagnosis can be performed with a simple configuration without affecting the operation, and it is possible to secure inexpensive and high reliability.

In each of the embodiments described above, each channel is formed with the same configuration and has the same characteristics. However, the characteristics may be slightly different depending on the parts used. In some cases, the characteristics are intentionally set to have different characteristics.

Accordingly, a configuration assuming that the channels have exactly the same characteristics (the same characteristics) may cause erroneous diagnosis.

In such a case, the comparison circuit 5
It is a simple, inexpensive and highly reliable method to set the comparison reference of 0 and 82 in correspondence with the channel to be diagnosed, and it is preferable.

That is, the comparison circuits 50 and 82 can change the output inversion voltage by a resistance value generally attached to the outside.

Therefore, an electronic potential meter is used for the externally mounted resistor, the value of the electronic potentiometer is specified from the outside (for example, a CPU), and the diagnosis is performed in consideration of the characteristics of each channel. The performance is improved.

[0065]

As described above, according to the present invention,
High reliability, low cost, and self-diagnosis function
Self-diagnosis can be easily performed.

Further, when a plurality of analog output circuits are provided and made redundant, the standby analog output circuit is automatically operated according to the diagnosis result, so that the reliability is improved and the control section is improved. Load can be reduced.

Further, since a CR filter is provided between the D / A converter and the output buffer, even if the input value of the D / A converter is temporarily changed at the time of diagnosis, the output buffer of the channel is not changed. The output is no longer affected,
Diagnosis can be performed even while the analog output circuit is operating, and convenience is improved.

Further, since the output of the comparison circuit can be held, the output of the output buffer in the channel can be prevented from being affected.

Further, since the channel used for the diagnosis is provided exclusively, it is possible to prevent the diagnosis processing from affecting the operation state.

Further, since the diagnosis result is notified by the LED or the like, the diagnosis result can be easily understood.

Further, since the determination means such as the OR buffer is provided, even if the analog output circuit is provided with a plurality of channels, it is easy to determine whether or not there is an abnormality in the analog output circuit. .

Further, since the counting means is provided, accurate diagnosis can be performed from a plurality of diagnosis results, and erroneous diagnosis due to a temporary cause can be prevented.

Further, a comparison reference setting device for setting a comparison reference in the comparison circuit is provided so that differences in circuit characteristics and the like can be adjusted, so that reliability is improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an analog output device applied to a description of a first embodiment of the present invention.

FIG. 2 is a diagram showing a diagnostic procedure of the analog output device shown in FIG.

FIG. 3 is a schematic configuration diagram of an analog output device having a configuration alternative to FIG. 1;

FIG. 4 is a schematic configuration diagram of an analog output device having a configuration replacing FIG. 1;

FIG. 5 is a schematic configuration diagram of an analog output device having a configuration replacing FIG. 1;

FIG. 6 is a schematic configuration diagram of an analog output device having a configuration replacing FIG. 1;

FIG. 7 is a schematic configuration diagram of an analog output device applied to the description of a second embodiment of the present invention.

FIG. 8 is a schematic configuration diagram of an analog output device applied to a description of a conventional technique.

[Explanation of symbols]

 Reference Signs List 10 input buffer 20 (21, 22) D / A converter 30 (31, 32) output buffer 40 (41, 42) CR filter circuit 50 (51, 52), 82 comparison circuit 81 multiplexer 83, 84 notification means 85 OR Buffer 86 Counter 89 Output selector

Claims (9)

[Claims] A plurality of channels including at least a D / A converter for converting a digital signal into an analog signal and an output buffer for stably outputting an analog signal from the D / A converter; An analog output device having an analog output circuit provided with an input buffer for inputting a digital signal of a predetermined value to the D / A converter of a predetermined channel based on a signal from a control unit, wherein the control unit has a predetermined channel When the diagnosis is instructed, one channel not to be diagnosed is set as a comparison channel, and a digital signal having the same value as that of the channel to be diagnosed is input to the D / A converter of the comparison channel. The output of the A converter is compared with the output of the output buffer in the channel to be diagnosed. Analog output apparatus characterized by comprising a diagnostic means for determining that the channel is abnormal. 2. The system according to claim 1, wherein two or more analog output circuits are provided, and when one is in operation, the other is on standby to form a redundant circuit, and when there is an abnormality in a channel to be diagnosed, the circuit is output from the diagnostic means. 2. The analog output device according to claim 1, further comprising an operation switching unit that sets the analog output circuit in operation to a standby state by a signal, and sets the analog output circuit in the standby state to an operation state. 3. The diagnosing means is provided between the D / A converter and an output buffer, so that even if an input value of the D / A converter is temporarily changed at the time of diagnosis, the diagnosing means may be used. 3. The analog output device according to claim 1, further comprising a CR filter configured to prevent an output of the output buffer from being affected. 4. A diagnostic circuit comprising: a comparing circuit for comparing the output of an output buffer in a diagnostic channel with the output of a D / A converter in a comparison channel and holding the output. The analog output device according to claim 1, wherein: 5. A diagnostic D / A converter for inputting a digital signal having the same value as a value input to a D / A converter of a diagnostic channel at the time of diagnosis, and a D / A converter for each channel. Output selecting means for selecting and outputting an analog signal from the D / A converter of the diagnostic channel among analog signals from the A converter, and a signal from the output selecting means and a signal from the diagnostic D / A converter. 4. The analog output device according to claim 1, further comprising a comparison circuit configured to compare a signal with an output of the analog output device. 6. An LE for notifying an output state of the comparison circuit.
The analog output device according to claim 4, further comprising a notification unit such as D. 7. An output of the comparison circuit in a plurality of channels is input, and at least one of the channels is output.
5. An apparatus according to claim 4, further comprising: an OR buffer for outputting a signal indicating the occurrence of an abnormality.
Or the analog output device according to 5. 8. The analog output device according to claim 7, wherein said judging means has a counting means for counting a diagnosis result when a plurality of diagnoses are performed intermittently. 9. The analog output device according to claim 4, further comprising a comparison reference setting device for setting a comparison reference in said comparison circuit.