JPH06265605A - Electronic circuit used in radiation environment - Google Patents

Abstract

(57) [Summary] [Construction] An operating state detecting means 1 for electronic circuits 3 and 5, an input switching means 4, 10 and 11 for electronic circuits, and a characteristic deterioration detecting means 2 for detecting characteristic deterioration of electronic circuits are provided. The operating state detecting means detects that the output of the electronic circuit is not in use, the characteristic deterioration detecting means 2 outputs a test signal to the input switching means, and the output of the electronic circuit is detected to detect the output of the electronic circuit. Characteristic deterioration can be detected. [Effect] It is possible to easily and early detect the characteristic deterioration of an electronic circuit under a radiation environment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to electronic circuits, and more particularly to
The present invention relates to an electronic circuit suitable for use in an environment such as a nuclear power plant that may be exposed to radiation.

[0002]

2. Description of the Related Art Conventionally, in a nuclear power plant, an electronic circuit including a semiconductor element is not installed in a storage container which is an environment exposed to radiation. However, it is expected that electronic circuits will be installed in the radiation environment in the future as the functions of sensors and control devices become more sophisticated. In addition, inspection and monitoring robots are being introduced in a radiation environment from the viewpoint of reducing radiation exposure. Since these robots are highly functional, a control circuit using an LSI such as a CPU or a memory or an operational amplifier (hereinafter referred to as an OP amplifier) is mounted inside.

It is known that semiconductor elements used in electronic circuits are vulnerable to radiation irradiation and their characteristics are deteriorated. Therefore, in order to prevent the electronic circuit from malfunctioning due to radiation, the radiation dose to the electronic circuit is estimated by calculating the radiation dose to the electronic circuit or measuring it with a radiation detector. It is conceivable to replace the electronic circuit before the amount exceeds the dose that deteriorates the electronic circuit.

However, it is known that the characteristic deterioration of the semiconductor element greatly changes depending on the type of radiation, the dose rate, the environmental temperature and the like. Further, it largely depends on the type of element and the manufacturing process. Therefore, it is difficult to predict the deterioration of the characteristics of the semiconductor device only by monitoring the radiation dose as described above.

For this reason, the same semiconductor element as the mounted IC is mounted as a sensor on each exchange circuit board of the electronic circuit, and deterioration of the sensor due to radiation can be monitored so that the circuit board can be replaced before the circuit board malfunctions. It is also considered to do. This is to measure changes in the amplification factor and threshold voltage of a semiconductor element and to issue an alarm when they exceed the threshold value.

However, such a sensor is not usually commercially available and needs to be newly developed. Further, as the number of types of IC increases, many types of sensors are required, which may be impractical.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide means for easily detecting the characteristic deterioration of an electronic circuit used in a radiation environment due to radiation.

[0008]

In order to achieve the above-mentioned object, the present invention has an operational state detecting means for the electronic circuit, an input switching means for the electronic circuit, and a characteristic deterioration for detecting characteristic deterioration of the electronic circuit. A detection means is provided.

[0009]

The operating state detecting means detects that the output of the electronic circuit is not in use, switches the input of the electronic circuit, and applies the input switching means to apply the test signal to the input terminal of the electronic circuit. Then, the characteristic deterioration detecting means is operated. The characteristic deterioration detecting means outputs the test signal to the input switching means and detects the output of the electronic circuit, whereby the characteristic deterioration of the electronic circuit can be detected.

[0010]

EXAMPLES Examples of the present invention will be described below. A circuit diagram of an embodiment of the present invention is shown in FIG. This embodiment is an embodiment for early detecting characteristic deterioration of the digital circuit 3 and the analog circuit 5 for taking in digital and analog signals from the plant due to radiation.

First, the structure of the apparatus will be briefly described. The control device 1 is a computer for controlling the plant. The digital circuit 3 and the analog circuit 5 take in the signals from the plant from the input terminals 30 and 32, respectively, and output the signals from the output terminals 31 and 33. The signals from the output terminals 31 and 33 are input to the control device 1 and used as plant information data, but they are omitted in this figure. The characteristic deterioration detecting device 2 checks the operation of the digital circuit 3 or the analog circuit 5 by utilizing the idle time when the control device 1 does not use the data from the digital circuit 3 or the analog circuit 5. Here, the control device 1 and the characteristic deterioration detection device 2 are installed in a place that is not exposed to radiation.

The operation of this embodiment will be described below with reference to FIGS. 1 and 2. FIG. 2 shows an operation flowchart of the characteristic deterioration detecting device 2. The operation of the characteristic deterioration detecting device 2 will be described in the order of numbers L1 to L6 in the flowchart.

L1: The characteristic deterioration detecting device 2 takes in the operation state signal 20 from the control device 1 and judges whether or not the test is possible. When the operation state signal 20 is in the testable state, that is, when the control device 1 is not controlling the plant using the outputs of the digital circuit 3 and the analog circuit 5, the process proceeds to L2.

L2: Digital circuit 3 and analog circuit 5
Conduct the test. Perform deterioration diagnosis of each circuit. Details of the diagnostic method will be described later.

L3: L4 when an abnormality is found in the circuit
If normal, proceed to L5.

L4: An abnormality detection signal 26 is output to the control device 1 when an abnormality is found in the circuit.

L5: L until the diagnosis of the two circuits is completed
Repeat 2 to L5.

L6: When the control device 1 shuts down, the characteristic deterioration detecting device also ends its operation.

Next, a method of diagnosing the digital circuit 3 and the analog circuit 5 will be described with reference to FIGS. First, a method of diagnosing the digital circuit 3 will be described. For simplicity, this digital circuit is a CMOS with 1 input and 1 output.
The characteristic deterioration detecting device 2, which is an inverter circuit, outputs the relay control signal 22 to the switch 4. As a result, the input of the digital circuit 3 is switched to the test signal 21 from the input terminal 30 from the plant, and the test signal can be input.

FIG. 3 shows the relationship between the input and output voltages of the digital circuit. A digital circuit is normally input with a voltage of 0 (low level) or 5 V (high level) corresponding to logic 0 or 1, respectively. The output is also 0
Or a voltage of 5V. Therefore, since the digital circuit 3 is an inverter, as shown in FIG. 3, when 5V is input, 0V is output, and when 0V is input, 5V is input.
Is output. The input voltage level actually has a permissible range, and 0 to 1.5 when the circuit is operating normally.
V is recognized as a low level and 3.5 to 5V is recognized as a high level, and a normal output is obtained.

However, in the CMOS circuit, when the threshold voltage of the internal MOSFET changes due to radiation irradiation, the circuit characteristics also change. That is, the low level range and the high level range of the input change, and the upper limit value of the low level voltage decreases, for example. Therefore, if the circuit operation is checked by inputting the low level voltage upper limit value of 1.5 V and the high level voltage lower limit value of 3.5 V instead of the normal 0 and 5 V, a normal output can be obtained with normal input. However, the test input gives an abnormal output. Therefore, if the characteristic deterioration detecting device 2 monitors the output signal 24 of the digital circuit 3, the abnormality of the circuit can be detected at an early stage.

Next, a method of diagnosing the analog circuit 5 will be described. The analog circuit 5 is a signal amplifier using an OP amplifier 6. The characteristic deterioration of the input resistance 8 and the feedback resistances 7 and 9 due to radiative transition is extremely small. Therefore, the characteristic deterioration of the analog circuit 5 is due to the characteristic deterioration of the OP amplifier 6.

The OP amplifier 6 is an inverting amplifier for inputting and amplifying a signal through the input resistor 8. The amplification degree is determined by the input resistance 8 and the feedback resistance 7. That is,
When the resistance value of the input resistor 8 is R8 and the resistance value of the feedback resistor 7 is R7, the amplification degree G is calculated by the following equation.

[0024]

[Equation 1] G = -R7 / R8 When the characteristics of the OP amplifier 6 deteriorate due to radiation irradiation, the open loop gain decreases and the amplification degree G decreases, so the output when a constant input signal voltage is input decreases. To do. Therefore, if the output change when the test signal is input is monitored, the characteristic deterioration of the OP amplifier 6 can be known. However, in the negative feedback amplifier, the error of the amplification degree is reduced to about 1 / open-loop gain. Therefore, when the amplification degree G is small, the characteristic deterioration of the OP amplifier does not easily appear in the output. For this reason, in this embodiment, the feedback resistor 7 is switched to the high-resistance feedback resistor 9 at the time of diagnosis to perform the abnormality diagnosis. In this embodiment, the input resistance 8 is 1 kΩ.
In addition, the feedback resistor 7 is set to 10 kΩ and the amplification degree is -10. However, at the time of diagnosis, 1 MΩ of the feedback resistor 9 is used and the amplification degree is set to −1000 so that characteristic deterioration can be detected with higher sensitivity.

The diagnostic procedure of the analog circuit 5 will be described below. The characteristic deterioration detecting device 2 outputs the relay control signal 23 to the switches 10 and 11. This allows the analog circuit 5
Is the test signal 21 from the input terminal 32 from the plant.
And the test signal can be input. At the same time, the feedback resistance is also switched to the feedback resistance 9 for diagnosis. As the test signal 21, a DC voltage of 1 mV is input. Therefore, 1 V is output to the output signal 25 in the normal state. However, when the characteristics of the OP amplifier 6 deteriorate due to radiation irradiation and the open loop gain decreases, the output signal 25 also decreases, and the deterioration of the characteristics of the analog circuit 5 can be detected early by the characteristic deterioration detecting device 2.

[0026]

According to the present invention, it is possible to provide means for easily detecting characteristic deterioration of an electronic circuit used in a radiation environment.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an operation flowchart of the characteristic deterioration detecting device.

FIG. 3 is a characteristic diagram of input / output voltage of a digital circuit.

[Explanation of symbols]

1 ... Control device, 2 ... Characteristic deterioration detection device, 3 ... Digital circuit, 4, 10, 11 ... Switch, 5 ... Analog circuit,
6 ... OP amplifier, 7, 9 ... Feedback resistance, 8 ... Input resistance, 20 ... Operating state signal, 21 ... Test signal, 22,
23 ... Relay control signal, 24, 25 ... Output signal, 26 ...
Abnormality detection signals, 30, 32 ... Input terminals, 31, 33 ... Output terminals.

Claims (3)

[Claims] 1. In an electronic circuit used in a radiation environment, an operating state detecting means for detecting that the output of the electronic circuit is in an unused state, the input of the electronic circuit is switched, and a test signal is output. Input switching means applied to the input terminal of the electronic circuit, and output of the test signal to the input switching means according to an instruction from the operating state detecting means, and detection of the output of the electronic circuit causes deterioration of characteristics of the electronic circuit. An electronic circuit used in a radiation environment, characterized by being provided with a characteristic deterioration detecting means for detecting. 2. The output signal of the characteristic deterioration detecting means according to claim 1, which is a signal including a low level input upper limit voltage and a high level input lower limit voltage of the logic signal, and confirms the operation of the logic circuit portion of the electronic circuit. An electronic circuit used in a radiation environment that has the function of 3. The electronic circuit according to claim 1, wherein the output signal of the characteristic deterioration detecting means is a minute voltage signal and has a function of confirming the operation of the analog circuit portion of the electronic circuit.