JPH057155A - Output circuit with characteristic check function - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an output circuit with a characteristic check function that enables inspection of the output circuit while the system is operating by adding a test circuit to the output circuit. The D / A converter includes a detection circuit for detecting a signal output from the D / A converter and a signal simulation circuit for adding a test signal to an input signal of the D / A converter. A correction circuit for adding / subtracting the test signal component from the output signal is provided. In addition, by operating the signal simulation circuit, D from the detection signal output from the detection circuit and the input signal of the D / A converter.
An arithmetic circuit for collecting input / output characteristic data of the A / A converter;
Further, a detection circuit for rechecking the soundness of correction of the correction circuit is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog signal output circuit used in a digital controller or the like, and more particularly to an output circuit with a characteristic check function capable of inspecting the output circuit while the controller is operating.

[0002]

2. Description of the Related Art Regarding the inspection of digital control devices used in various plants, usually, the operation of the entire system using the control device to be inspected is temporarily stopped, the control software of the control device is checked, and external control is performed. The operation of the input / output circuit that carries out the signal connection is checked. The input / output circuit has an analog input / output circuit and a digital input / output circuit. To check the operation of the analog input / output circuit, consider the secular change of the analog part and collect the input / output characteristic data at regular intervals. It is necessary to confirm that the data is within the specified accuracy.

An inspection of a conventional analog output circuit that outputs a signal to an actuator will be described as an example with reference to the block diagram of the output circuit shown in FIG. The output circuit 1 is installed in the control panel of the digital control device as a component of the digital control device, replaces a digital input signal with a current value which is a command value to the actuator 2, and outputs the signal via the output signal line 3. It outputs to 2. A digital / analog converter (hereinafter abbreviated as D / A converter) 4 is built in the output circuit 1 and has an input signal S.
_{By 1} , the value corresponding to this is output via the output signal line 3 as an analog current signal.

When the output circuit 1 is inspected,
After temporarily stopping the operation of the entire system using this digital control device, the actuator 2 is disconnected from the output signal line 3, and the test current measuring device 5 separately prepared is connected to the output signal line 3. Therefore, the input signal S ₁ of the D / A converter 4 is changed stepwise within the signal input range, and D
The current signal output from the / A converter 4 is read by the test current measuring device 5. The soundness of the output circuit 1 is confirmed by whether the input / output characteristics of the output current value with respect to this input signal satisfy the instrument accuracy of the D / A converter 4.

The confirmation of the input / output characteristics of the D / A converter 4 not only finds a malfunction of the D / A converter 4 but also gives a symptom leading to malfunction by regularly collecting data. It is possible to find it and therefore this inspection work should be carried out regularly.

[0006]

The conventional soundness confirmation of the output circuit 1 cannot be frequently performed because it is necessary to stop the operation of the entire system using the output circuit 1. Therefore, the period between inspections tends to be long, and if a problem occurs in the input / output characteristics of the D / A converter 4 during this period, the discovery will be delayed and the operation of the entire system will be delayed. There was a risk that it would have an impact.
In addition, the inspection performed by stopping the operation of the entire system,
Since many output points are carried out at once, there is a problem that a lot of time and man-hours are spent for these inspections.

It is an object of the present invention to provide an output circuit with a characteristic check function, which makes it possible to inspect the output circuit while the system is operating by adding a test circuit to the output circuit. ..

[0008]

SUMMARY OF THE INVENTION The present invention provides a detection circuit for detecting a signal output from a D / A converter to a conventional output circuit, and a signal for adding a test signal to an input signal of the D / A converter. A correction circuit for adding and subtracting a test signal component from the output signal of the D / A converter is provided by adding a simulation circuit. An arithmetic circuit for operating the signal simulation circuit to collect input / output characteristic data of the D / A converter from the detection signal output from the detection circuit and the input signal of the D / A converter, and further the correction circuit. A detection circuit is provided to recheck the soundness of circuit correction.

[0009]

The input of the D / A converter is changed within the range of use of the D / A converter by adding the test signal to the input signal input to the D / A converter. Input / output characteristic data of the D / A converter is collected by measuring the output data. As the output of the output circuit, the value of the test signal is corrected from the output signal of the D / A converter including the test signal, the original output signal is output, and the soundness of the correction is rechecked. To do.

[0010]

An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those of the above-described conventional technique are denoted by the same reference numerals and detailed description thereof will be omitted. FIG. 1 is a block diagram of an output circuit with a characteristic check function. The output circuit with a characteristic check function 10 inputs an input signal S ₁ which is a command value to an actuator 2 and outputs a current signal via an output signal line 3. Is output to the actuator 2 as. The built-in signal simulation circuit 11 inputs the input signal S ₁ and the simulation command signal S ₂ which is a test signal, selects both depending on the situation and outputs them as the D / A converter input signal S ₃ . In the circuit, the D / A converter 4 is a digital D / A converter input signal S ₃ from the signal simulation circuit 11.
Is input, converted into an analog signal, and output.

Further, the first detection resistor 12 and the second detection resistor 13 are inserted in the output signal line 3 and a current flows through the output signal line 3 to generate a voltage proportional to the current across the output signal line 3. It is resistance. Detection circuit 14
The correction detection circuit 15 inputs the voltage generated across the first detection resistor 12 and the voltage generated across the second detection resistor 13 via the switching contact 16, and outputs the D / A converter output signal S ₄ and the actuator 2 respectively. And outputs a command signal output to the circuit confirmation signal S ₅ . The correction circuit 17 is a circuit for inputting the correction signal S ₆ from the arithmetic circuit 18 and outputting a correction current to the output signal line 3, and the arithmetic circuit 18 outputs D from the detection circuit 14.
Input the A / A converter output signal S ₄ and the input signal S ₁ ,
The input / output characteristics of the D / A converter 4 are calculated, and the simulation command signal S ₂ and the correction signal S ₆ are output to the signal simulation circuit 11 and the correction circuit 17, respectively. The arithmetic circuit 18 outputs the data output signal S ₇ to a recording device (not shown) in order to leave the recording. The switching contact 16 is a contact for switching the detection circuit 14, the correction detection circuit 15, and the correction circuit 17, and another circuit that outputs a signal of another actuator not shown in the drawing.

Next, the operation of the above configuration will be described. As an example, the case of inputting 25% of the input signal S ₁ will be described. The output circuit with characteristic check function 1
When checking the circuit outputting to the actuator 2 in 0, first, the switching contact 16 is turned “ON” to connect the detection circuit 14, the correction detection circuit 15 and the correction circuit 17 to the output signal line 3. Here, assuming that the signal input range of the input signal S ₁ is 0 to 100%, the D of the D / A converter 4 before inspection is
/ A converter input signal S ₃ is the same as input signal S ₁ 25%
Is input and the output range is 4 to 20 mA, 8 mA corresponding to 25% flows in the output signal line 3.
Here, the correction circuit 17 does not perform correction.

When confirming the output value when the D / A converter 4 receives the 0% signal, the arithmetic circuit 18 outputs a 0% simulation command signal S ₂ to the signal simulation circuit 11. Here, the signal simulation circuit 11 forces the D / A regardless of the input signal S _1.
The converter input signal S _{3 is set} to 0%. Since the D / A converter input signal S ₃ is 0% in the D / A converter 4, a current equivalent to 4 mA flows through the output signal line 3 on the output side. The arithmetic circuit 18 compares the D / A converter output signal S ₄ with respect to the simulated command signal S ₂ with a calculated value to calculate a meter error, and also compares the D / A converter output signal S ₄ with a previously stored meter accuracy to calculate the D / A. The quality of the operation of the converter 4 is determined. The arithmetic circuit 18 can also store this test data and output it as a data output signal S ₇ .

Here, the arithmetic circuit 18 outputs the simulation command signal S ₂ and at the same time inputs the error component (+ 25% equivalent signal) between the input signal S ₁ and the simulation command signal S ₂ to the correction circuit 17 as the correction signal S _6. A current of 4% corresponding to 25% as an output signal of the correction circuit 17 is added to the output signal line 3 to obtain the original command value of 25% (8 mA). The correction detection circuit 15 outputs a circuit confirmation signal S ₅ for rechecking the soundness of the corrected command value to the arithmetic circuit 18.

As a result, in the arithmetic circuit 18, the input signal S ₁
And the circuit confirmation signal S ₅ are compared and checked that there is a one-to-one correspondence. When the one-to-one correspondence is not established, an alarm signal S ₈ is output to the alarm device 19. At the same time as notifying, the switching contact 16 is turned "OFF" to detect the detection circuit 1
4 and the correction detection circuit 15 and the correction circuit 17 are disconnected from the output signal line 3 to stop the test. The above operation is D
0%, 25%, 50% of the signal input range of the / A converter 4,
It is possible to know the input / output characteristics of the D / A converter 4 in the entire input range by carrying out at 100%.

As a result, the output circuit 1 with the characteristic check function is provided.
0 means that the signal from the D / A converter 4 does not stop the system, does not need to be disconnected, and does not affect the command value to the actuator 2; You can check the characteristics. Further, it is possible to recheck the soundness of the corrected command value.

[0017]

As described above, according to the present invention, it is possible to check the soundness confirmation work of the output circuit without stopping the operation of the entire system using the output circuit. This makes it possible to inspect in a short cycle, and
It is possible to detect signs of A converter failure in advance,
It is possible to prevent serious accidents due to malfunctions. Further, there is an effect that the inspection performed by stopping the operation of the entire system can be completed in a short time.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an output circuit with a characteristic check function of the present invention.

FIG. 2 is a block configuration diagram of a conventional output circuit.

[Explanation of symbols]

2 ... Actuator, 3 ... Output signal line, 4 ... Digital / analog converter (D / A converter), 10 ... Output circuit with characteristic check function, 11 ... Signal simulation circuit, 12 ... First
Detection resistor, 13 ... second detection resistor, 14 ... detection circuit,
15 ... Correction detection circuit, 16 ... Switching contact, 17 ... Correction circuit, 18 ... Arithmetic circuit, 19 ... Alarm device.

Claims (1)

Claim: What is claimed is: 1. An output circuit for inputting a digital signal, converting the signal into an analog signal and outputting the analog signal, and a digital / analog converter for converting the digital signal into an analog signal, and a digital command value for the actuator. A signal simulating circuit for simulating an input signal of the digital-analog converter by adding a test signal to the input signal, a detection circuit for detecting an output signal of the digital-analog converter, and the digital-analog converter Input signal and the detection signal of the detection circuit to collect the characteristic data of the digital-analog converter, and to calculate an error by comparing the characteristic data with a reference value;
An output circuit with a characteristic check function, comprising a correction circuit for adding / subtracting the test signal equivalent to an output signal of an analog converter, and a correction detection circuit for checking the quality of correction of the output signal by the correction circuit.