Deterioration Diagnosis System

Abstract

To enable the diagnosis of silicon-based operational amplifier degradation even in high-radiation environments. [Solution] The system comprises a first operational amplifier 11 made of silicon, a second operational amplifier 12 made of a semiconductor with a larger band gap than silicon, a subtraction circuit 10 that subtracts the output of the first operational amplifier 11 from the output of the second operational amplifier 12, a database 4 in which information on the degradation of the outputs of the silicon operational amplifier and the operational amplifier made of a semiconductor with a larger band gap than silicon due to radiation is registered, and a diagnostic unit 3 that diagnoses the degradation of the first operational amplifier 11 from the output of the subtraction circuit 10 and the information registered in the database and outputs a diagnostic result.

Description

[Technical Field]

[0001] This invention relates to a degradation diagnosis system for diagnosing the degradation of operational amplifiers in high-radiation environments. [Background technology]

[0002] In recent years, there has been a growing need to inspect and measure various physical quantities, such as temperature, water level, pressure, and radiation, in order to monitor and understand the condition of nuclear power plants and equipment. The semiconductor circuits that make up the measuring instruments used to measure these physical quantities can degrade due to radiation, and therefore, a means of confirming the integrity of these semiconductor circuits is necessary.

[0003] Radiation-induced degradation of operational amplifiers (op-amps), commonly used in semiconductor circuits, can lead to a decrease in output power, resulting in poor performance of measuring instruments. Since op-amps amplify power according to the potential difference between input terminals using a differential amplifier circuit composed of at least two transistors, degradation of individual transistors reduces the performance (failure) of the op-amp as a whole.

[0004] For example, Patent Document 1 discloses a method for transmitting test data to a semiconductor circuit (measuring instrument) to be diagnosed and performing an anomaly diagnosis from the returned data. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-253995 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, when the object to be diagnosed is in a radiation environment, adding a diagnostic unit (diagnostic circuit) to the measuring instrument to be diagnosed may increase the risk of failure due to radiation. For this reason, it has been difficult to apply the method described in Patent Document 1 to measuring instruments in high-radiation environments.

[0007] Furthermore, the method for diagnosing faults from the output of measuring instruments described in Patent Document 1 makes it difficult to determine which part of the semiconductor circuit is degraded, and it is difficult to determine whether the problem can be addressed by calibrating the measuring instrument or whether the measuring instrument needs to be replaced.

[0008] The inventors have experimentally demonstrated that when analog equipment is used in radiation environments with higher radiation levels than typical radiation environments such as nuclear power plants (hereinafter referred to as "high-radiation environments"), the degradation of silicon (Si) operational amplifiers, which constitute the circuits within such equipment, is particularly pronounced. Specifically, this phenomenon involves the accumulation of charge at the oxide layer interface due to ionization caused by radiation, leading to an increase in offset voltage. As the amount of accumulated charge increases, the response eventually disappears, and the operational amplifier completely fails.

[0009] Given the above circumstances, there was a need for a method that could accurately diagnose the radiation-induced degradation of silicon-based operational amplifiers even in high-radiation environments. [Means for solving the problem]

[0010] To solve the above problems, a degradation diagnosis system according to one aspect of the present invention comprises: a first operational amplifier made of silicon; a second operational amplifier made of a semiconductor with a larger band gap than silicon; a subtraction circuit that subtracts the output of the first operational amplifier from the output of the second operational amplifier; a database in which information on the degradation of the outputs of the silicon operational amplifier and the semiconductor with a larger band gap than silicon due to radiation is registered; and a diagnostic unit that diagnoses the degradation of the first operational amplifier from the output of the subtraction circuit and the information registered in the database and outputs a diagnostic result. [Effects of the Invention]

[0011] According to at least one aspect of the present invention, radiation-induced degradation of silicon operational amplifiers can be accurately diagnosed even in high-radiation environments. Other issues, configurations, and effects not mentioned above will be clarified by the following description of embodiments for carrying out the invention. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example configuration of a deterioration diagnosis system according to the first embodiment of the present invention. [Figure 2] This figure shows an example of the hardware configuration of a computer used in a degradation diagnosis system according to an embodiment of the present invention. [Figure 3] This figure shows an example of the radiation degradation characteristics of Si operational amplifiers and SiC operational amplifiers. [Figure 4] This figure shows an example of the structure of an output degradation database according to the first embodiment of the present invention. [Figure 5] This figure shows an example of a calibration method for a measuring instrument according to the first embodiment of the present invention. [Figure 6] This figure shows an example configuration of a deterioration diagnosis system according to a second embodiment of the present invention. [Figure 7] This is a schematic diagram showing an example of the configuration of a measuring instrument that implements a diagnostic circuit for a deterioration diagnosis system according to a third embodiment of the present invention. [Figure 8] This is a schematic diagram showing an example of the configuration of a measuring instrument that implements a diagnostic circuit for a deterioration diagnosis system according to the fourth embodiment of the present invention. [Modes for carrying out the invention]

[0013] Hereinafter, examples of embodiments for carrying out the present invention (hereinafter referred to as "embodiments") will be described with reference to the attached drawings. In the present specification and the accompanying drawings, common or similar constituent elements are denoted by the same reference numerals, and repeated descriptions are omitted. Further, when there are a plurality of identical or similar constituent elements, descriptions may be given by adding different suffixes to the same reference numerals. Note that when it is not necessary to distinguish between these plurality of constituent elements, the descriptions may be given with the suffixes omitted. Unless otherwise specified, the number of each constituent element may be singular or plural.

[0014] <First Embodiment> First, the configuration of a degradation diagnosis system according to the first embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is a diagram showing a configuration example of the degradation diagnosis system according to the first embodiment of the present invention. As shown in FIG. 1, the degradation diagnosis system 1 of the present embodiment includes a diagnostic circuit 2, a diagnosis unit 3, and an output degradation database (referred to as "DB" in the drawings) 4.

[0015] The diagnostic circuit 2 includes an operational amplifier (hereinafter referred to as "Si operational amplifier") 11 configured using silicon (Si) as a material of a semiconductor element, an operational amplifier (hereinafter referred to as "SiC operational amplifier") 12 configured using silicon carbide (SiC), a subtraction circuit 10, the diagnosis unit 3 that measures and diagnoses an output of the subtraction circuit 10, and the output degradation database 4.

[0016] The subtraction circuit 10 includes a SiC operational amplifier 13 (an example of a third operational amplifier) to which respective output signals of the Si operational amplifier 11 and the SiC operational amplifier 12 are input, and resistors R1 to R4. The SiC operational amplifier 13 outputs a signal corresponding to a difference between respective output signals (voltage values) of the Si operational amplifier 11 and the SiC operational amplifier 12. SiC is a semiconductor having a larger band gap than Si.

[0017] The inverting input terminal (-) and non-inverting input terminal (+) of the Si operational amplifier 11 and SiC operational amplifier 12 are grounded. The output terminal of the Si operational amplifier 11 is connected to the inverting input terminal (-) of the SiC operational amplifier 13 via resistor R1. The output terminal of the SiC operational amplifier 12 is connected to the non-inverting input terminal (+) of the SiC operational amplifier 13 via resistor R3. The non-inverting input terminal (+) of the SiC operational amplifier 13 is grounded via resistor R4. The output terminal of the SiC operational amplifier 13 is connected to the inverting input terminal (-) via resistor R2 and is also connected to the diagnostic unit 3.

[0018] Output signal V of Si operational amplifier 11 off1 This is input to the inverting input terminal (-) of the SiC operational amplifier 13 via resistor R1. The output signal V of the SiC operational amplifier 12 off2 This signal is input to the non-inverting input terminal (+) of the SiC operational amplifier 13 via resistor R3. The SiC operational amplifier 13 receives the output signal V from the Si operational amplifier 11. off1 The output signal Voff2 of the SiC operational amplifier 12 is subtracted from this signal, and the subtraction result is output. The output signal Vo of the SiC operational amplifier 13 is input to the diagnostic unit 3 and is also fed back to the inverting input terminal (-) via resistor R2.

[0019] Since the output of the subtraction circuit 10 is amplified by the ratio of resistors R1 and R2, the values ​​of resistors R1 and R2 can be arbitrarily determined according to the magnitude of the offset voltage. While resistors R3 and R4 can also be arbitrarily determined, for ease of calculation, it is desirable to set the values ​​of resistors R1 to R4 to R1=R3 and R2=R4. When R1=R3 and R2=R4, the output of the SiC op-amp 13 is R2 / R1(V off1 -V off2 It is represented as ).

[0020] Positive power supply V for Si op-amp 11, SiC op-amp 12, and SiC op-amp 13 dd and negative power supply V ssThese are all common power supplies. Note that the inverting input terminal (-) and non-inverting input terminal (+) of Si op-amp 11, SiC op-amp 12, and SiC op-amp 13 may be swapped.

[0021] In the diagnosis of Si operational amplifiers according to this embodiment, the Si operational amplifier with the lowest radiation resistance among the circuits constituting the measuring instrument to be diagnosed is targeted. Furthermore, it is desirable that Si operational amplifier 11 is an operational amplifier with the same specifications as the targeted Si operational amplifier (for example, the semiconductor material is the same, the structure is the same, etc.).

[0022] The diagnostic circuit 2 is installed in an environment with relatively high radiation levels (high-radiation area). The diagnostic unit 3 and the output degradation database 4 are preferably installed in an environment with low radiation levels (low-radiation area). For example, in the case of a nuclear power plant, the diagnostic unit 3 and the output degradation database 4 are installed in the central control panel of the central control room.

[0023] When the diagnostic circuit 2 on the high-radiation region side is irradiated with radiation, electron-hole pairs are generated in the semiconductor element used in the operational amplifier due to the Compton effect, and fixed charges and interface states are formed at the interface between the insulating layer and the semiconductor layer. This effect causes fluctuations in the offset voltage, degrading the characteristics of the semiconductor element. The inventors have newly discovered that this effect is more pronounced the smaller the semiconductor band gap of the semiconductor layer, and up to the kGy order, only the Si operational amplifier experiences an increase in offset voltage, while the SiC operational amplifier shows almost no fluctuation. Therefore, in the diagnostic circuit 2 located in the high-radiation region, by using a comparison SiC operational amplifier 12 and a subtraction SiC operational amplifier 13, the offset voltage of the Si operational amplifier 11 can be measured and diagnosed in the diagnostic unit 3.

[0024] The operational amplifier used in the subtraction circuit 10 is preferably made of SiC, which has excellent radiation resistance, but any operational amplifier made of a semiconductor with a larger band gap than Si will suffice. For example, gallium nitride (GaN) or diamond semiconductor may be used as other semiconductors with a larger band gap than Si.

[0025] The output degradation database 4 stores information regarding the degradation of the outputs of the Si operational amplifier and the SiC operational amplifier due to radiation (e.g., gamma rays). In this embodiment, the output degradation database 4 records the change (transition) of the offset voltage corresponding to the radiation dose (cumulative absorbed dose) of the Si operational amplifier 11 and the change (transition) of the offset voltage corresponding to the radiation dose (cumulative absorbed dose) of the SiC operational amplifier 12. By comparing (referencing) the difference in offset voltages between the Si operational amplifier 11 and the SiC operational amplifier 12 measured by the diagnostic unit 3 with the data registered in the output degradation database 4, it becomes possible to understand the amount of radiation irradiated and absorbed by the Si operational amplifier 11 and the degree of degradation.

[0026] While it is possible to measure the offset voltage using the Si operational amplifier 11 alone, if the power supply voltage fluctuates due to radiation exposure, the fluctuations in the offset voltage due to radiation and the fluctuations in the reference value of the offset voltage due to the change in power supply voltage will coexist. As a result, it becomes difficult to accurately measure the degree of degradation of the Si operational amplifier 11 due to radiation.

[0027] Therefore, in this embodiment, a comparative operational amplifier (SiC operational amplifier 12) with excellent radiation resistance is installed in the diagnostic circuit 2, and the power supply voltage is set to be the same as that of the Si operational amplifier 11. This cancels out fluctuations in the power supply voltage for the Si operational amplifier 11, making it possible to accurately measure the change in the offset voltage of the Si operational amplifier 11.

[0028] Next, the hardware configuration of the computer used in the degradation diagnosis system 1 will be explained with reference to Figure 2. Figure 2 shows an example of the hardware configuration of the computer 20 included in the diagnostic unit 3. The computer 20 is an example of hardware used as a computer.

[0029] The computer 20 includes a CPU (Central Processing Unit) 21, ROM (Read Only Memory) 22, RAM (Random Access Memory) 23, an A / D converter 24, and a communication interface 26 connected to a system bus. The CPU 21, ROM 22, and RAM 23 are examples of control units.

[0030] The CPU 21 reads the program code for the software that implements the functions of the diagnostic unit 3 from the ROM 22, loads it into the RAM 23, and executes it. Variables and parameters generated during the CPU 21's calculation process are temporarily written to the RAM 23, and these variables and parameters are read out by the CPU 21 as needed. Another processor, such as an MPU (Micro Processing Unit), may be used instead of the CPU 21. In addition to the ROM 22, flash memory (semiconductor memory) may also be provided. Programs and databases can be permanently stored in the ROM 22 or flash memory.

[0031] The A / D (Analog / Digital) converter 24 converts the input analog signal into a digital signal and outputs it to the CPU 21.

[0032] The display device 25 is a monitor such as a liquid crystal display, and displays the GUI (Graphical User Interface) screen and the results of calculations performed by the CPU 21. The monitor 51 shown in Figures 7 and 8, which will be described later, is realized by the display device 25.

[0033] A communication device such as a NIC (Network Interface Card) is used for the communication interface 26. The communication interface 26 sends and receives various types of data to and from external devices via a communication network such as a LAN or a dedicated line connected to the communication device such as the NIC.

[0034] Next, the radiation degradation characteristics of Si operational amplifiers and SiC operational amplifiers will be explained with reference to Figure 3. Figure 3 shows an example of the radiation degradation characteristics of Si operational amplifiers and SiC operational amplifiers. The horizontal axis represents the radiation dose (cumulative absorbed dose), and the vertical axis represents the offset voltage of the operational amplifier.

[0035] When an operational amplifier is irradiated with radiation, electron-hole pairs are generated by the Compton effect, and fixed charges and interface states are formed at the interface between the insulating layer and the semiconductor layer. Our tests have shown that the smaller the semiconductor band gap of the semiconductor layer, the more susceptible it is to this effect.

[0036] When a Si operational amplifier is irradiated with radiation, its offset voltage increases in proportion to the cumulative absorbed dose (failure mode (1)). After the offset voltage has increased to a certain extent, it transitions to failure mode (2), where the amplification function is lost and there is no response. During failure mode (1), the increase in offset can be corrected by calibrating the measuring instrument on which the operational amplifier is implemented. However, once failure mode (2) occurs, it becomes impossible to correct the output of the measuring instrument by calibration. In the example in Figure 3, the Si operational amplifier transitions to failure mode (2) with an offset voltage on the order of several kGy.

[0037] SiC operational amplifiers also exhibit an increase in offset voltage, similar to Si operational amplifiers. However, due to their high bandgap and excellent radiation resistance, experiments by the inventors have confirmed that the change in offset voltage is almost negligible up to several hundred Gy to several MGy orders of magnitude.

[0038] Therefore, by using the offset voltage of the SiC operational amplifier 12 as a reference and taking the difference between that and the offset voltage of the Si operational amplifier 11, it becomes possible to accurately measure the change in the offset voltage of the Si operational amplifier 11. Here, since the output of the subtraction circuit 10 using the SiC operational amplifier 13 is either a positive or negative value, positive and negative values ​​are set as the threshold values ​​for degradation detection. In the example shown in Figure 3, the threshold values ​​are set to +5mV and -5mV, as shown by the two dashed lines.

[0039] Here, the structure of the output degradation database 4 will be explained with reference to Figure 4. Figure 4 shows an example of the structure of the output degradation database 4. The output degradation database 4 includes items for radiation dose (indicated as "Gy" in the figure), Si operational amplifier, SiC operational amplifier, and degradation judgment.

[0040] The "Radiation Dose (Gy)" field stores information indicating the radiation dose irradiated to Si and SiC operational amplifiers with the same configuration as the object being diagnosed. "Gy" is the unit of energy (absorbed dose) of radiation absorbed by a material. The Si operational amplifier section stores information indicating the voltage value (offset voltage) of the output signal of the Si operational amplifier that is irradiated with radiation. The SiC operational amplifier section stores information indicating the voltage value (offset voltage) of the output signal of the SiC operational amplifier that is irradiated with radiation.

[0041] The degradation judgment item stores information indicating the content of the degradation judgment when the radiation dose (Gy) irradiated to the operational amplifier to be diagnosed exceeds the value in the corresponding record. The diagnostic unit 3 determines the degradation of the Si operational amplifier 11 from the output from the subtraction circuit 10 (SiC operational amplifier 13) and the information registered in the output degradation database 4. For example, the diagnostic unit 3 determines "deviation from standard" when the radiation dose (Gy) is "35 Gy" and the voltage of the output signal of the Si operational amplifier 11 exceeds the threshold value of "5 mV". Also, the diagnostic unit 3 determines "failure" when the radiation dose (Gy) is "2500 Gy" and the output signal of the Si operational amplifier 11 is in a state where it cannot be measured (NG). At this time, when the radiation dose (Gy) is "35 Gy" and "2500 Gy", the offset voltage of each SiC operational amplifier is "0.4 mV" and does not fluctuate.

[0042] In this way, by detecting signs of failure in the Si operational amplifiers implemented in the measuring instrument based on the output degradation database 4, it becomes possible to accurately determine the replacement timing and perform the replacement work before the measuring instrument fails. The replacement work can be performed on a per-Si operational amplifier basis, but considering the work and settings (adjustments), it is also effective to replace the entire measuring instrument.

[0043] In this embodiment, the output degradation database 4 was described in table format, but other data formats may also be used.

[0044] Next, the calibration method for measuring instruments will be explained with reference to Figure 5. Figure 5 shows an example of a calibration method for measuring instruments. The horizontal axis represents time, and the vertical axis represents the output of the measuring instrument.

[0045] When the elapsed time from the start of radiation exposure (absorption) to the measuring instrument is zero, the radiation dose (Gy) is zero, and therefore the output of the measuring instrument is at the reference value. As the radiation dose (Gy) increases, the offset voltage of the Si operational amplifier used in the circuit of the measuring instrument increases (see Figure 3). Therefore, as the radiation dose (Gy) increases, the offset voltage of the Si operational amplifier increases, and the output of the measuring instrument deviates from the reference value, and the difference from the reference value increases.

[0046] Therefore, the output of the measuring instrument is calibrated at the moment (time t1) when the voltage value of the output signal of the Si operational amplifier exceeds a threshold (for example, ±5mV in Figure 3). As an example, the output of the measuring instrument is corrected (offset amount reset) by an amount equivalent to the fluctuation of the offset voltage. As a result, immediately after the output is calibrated at time t1, the output of the measuring instrument returns to the reference value. Note that as time passes and the radiation dose (Gy) increases, the offset amount increases again, and the output of the measuring instrument also gradually increases.

[0047] As described above, the degradation diagnosis system (degradation diagnosis system 1) according to this embodiment comprises: a first operational amplifier (e.g., Si operational amplifier 11) made of silicon; a second operational amplifier (e.g., SiC operational amplifier 12) made of a semiconductor with a larger band gap than silicon; a subtraction circuit (e.g., SiC operational amplifier 13) that subtracts the output of the first operational amplifier from the output of the second operational amplifier; a database (e.g., output degradation database 4) in which information on the degradation of the outputs of the silicon operational amplifier and the operational amplifier made of a semiconductor with a larger band gap than silicon due to radiation is registered; and a diagnosis unit (e.g., diagnosis unit 3) that diagnoses the degradation of the first operational amplifier from the output of the subtraction circuit and the information registered in the database and outputs a diagnosis result.

[0048] The degradation diagnosis system in this implementation, configured as described above, compares the output of a first operational amplifier using silicon with the output of a second operational amplifier using a semiconductor with a larger band gap than silicon, even in a high-radiation environment. This makes it possible to accurately measure the change in the offset voltage of the first operational amplifier using silicon, and to accurately diagnose the degradation of the first operational amplifier.

[0049] Therefore, it becomes possible to accurately determine the timing for calibration (e.g., resetting the offset voltage) and replacement of equipment placed in a high-radiation environment. Thus, the degradation diagnostic system according to this embodiment can provide highly reliable plant operation. For example, nuclear power plants continue to operate until the legally mandated periodic inspection (within 13 months), but by knowing the timing of replacement, it becomes easier to plan when to carry out replacement work during the periodic inspection.

[0050] <Second Embodiment> Next, the configuration of the deterioration diagnosis system according to the second embodiment of the present invention will be described with reference to Figure 6. Figure 6 shows an example of the configuration of a deterioration diagnosis system according to a second embodiment of the present invention. As shown in Figure 6, the degradation diagnosis system 1A of this embodiment does not have the subtraction circuit 10 (SiC operational amplifier 13) shown in Figure 1 in the diagnostic circuit 2A on the high-radiation region side, but instead has the function of the subtraction circuit 10 on the low-radiation region side. That is, a subtraction unit 30 (an example of a subtraction circuit) is placed in front of the diagnostic unit 3 located in the low-radiation region. The subtraction unit 30 subtracts the output signals of the Si operational amplifier 11 and the SiC operational amplifier 12, and the diagnostic unit 3 measures and diagnoses based on the subtraction result. For example, the subtraction unit 30 and the diagnostic unit 3 are located in the central control panel of the central control room.

[0051] The degradation diagnosis system 1A configured as described above can reduce the number of semiconductor elements (operational amplifiers) installed in the high-radiation area by one. As a result, the diagnostic circuit 2A can be made smaller than the diagnostic circuit 2 of the first embodiment.

[0052] Furthermore, since the subtraction unit 30 can be installed in a low-radiation area, it becomes unnecessary to consider radiation resistance when designing and selecting the subtraction unit 30. This makes it possible to design or select an inexpensive subtraction unit 30. For example, a subtraction unit 30 with the same functionality as the subtraction circuit 10 shown in Figure 1 can be configured using a microcontroller mounted on an integrated circuit. The subtraction unit 30 can be configured not only with analog circuits such as operational amplifiers, but also with digital circuits.

[0053] Alternatively, the subtraction unit 30 may be constructed using an operational amplifier made of a semiconductor with a larger band gap than Si (for example, SiC), as shown in the subtraction circuit 10 in Figure 1.

[0054] Next, a configuration in which the diagnostic circuits of the deterioration diagnosis systems according to the first and second embodiments described above are implemented in a measuring instrument will be explained with reference to Figures 7 and 8. There are two main methods for implementing the diagnostic circuits 2 and 2A, which have the SiC operational amplifier 12 shown in the first embodiment (Figure 1) and the second embodiment (Figure 6), into a measuring instrument. Each method will be explained below. (1) The diagnostic circuit is independent of the measurement circuit of the measurement instrument (see FIG. 7) (2) The Si operational amplifier in the measurement instrument is switched between the measurement circuit and the diagnostic circuit (see FIG. 8)

[0055] <Third Embodiment> Next, as a third embodiment, the configuration of (1) above, that is, the configuration in which the diagnostic circuit of the degradation diagnosis system is independent of the measurement circuit of the measurement instrument, will be described with reference to FIG. 7. FIG. 7 is a schematic diagram showing a configuration example of a measurement instrument mounted with a diagnostic circuit of a degradation diagnosis system according to a third embodiment of the present invention. As shown in FIG. 7, the measurement instrument 40 disposed in a high radiation region is connected to a central control panel 50. The measurement instrument 40 includes a control unit 42, a measurement circuit 41, and a diagnostic circuit 2.

[0056] The control unit 42 is configured of, for example, a microcontroller, and controls the entire interior of the measurement instrument 40 including the measurement circuit 41. The measurement circuit 41 is a circuit including a Si operational amplifier 11t, and outputs an output signal of the Si operational amplifier 11t corresponding to a physical quantity of a measurement object as a measurement result to a control device (not shown) of the central control panel 50 via a cable. The Si operational amplifier 11t is assumed to be the operational amplifier having the lowest radiation resistance among the measurement instrument 40. It is preferable that this Si operational amplifier 11t has the same specifications as the Si operational amplifier 11 of the diagnostic circuit 2. The diagnostic circuit 2 has the same configuration as the diagnostic circuit 2 shown in FIG. 1, and includes the Si operational amplifier 11, the SiC operational amplifier 12, and the subtraction circuit 10 configured of the SiC operational amplifier 13 and resistors R1 to R4.

[0057] At least the Si operational amplifier 11t of the measurement circuit 41 and each operational amplifier of the diagnostic circuit 2 share a common power supply voltage (positive power supply V dd , V ssThe control unit 42 controls the power supply to the measurement circuit 41 by switching switch S1 on and off, and controls the power supply to the diagnostic circuit 2 by switching switch S2 on and off. Switches S1 and S2 can also be considered as switching circuits.

[0058] The diagnostic circuit 2 of the measuring instrument 40, the diagnostic unit 3 located in the central control panel 50, and the output degradation database 4 constitute a degradation diagnostic system 1. In this degradation diagnostic system 1, the diagnostic unit 3 directly diagnoses the degradation of the Si operational amplifier 11, and based on the diagnosis result of the Si operational amplifier 11, it diagnoses the degradation of the Si operational amplifier 11t, which is the original target of diagnosis. This makes it possible to diagnose the degradation of the measuring circuit 41, which has the Si operational amplifier 11t, and consequently the measuring instrument 40.

[0059] The diagnostic unit 3 receives the output signal from the diagnostic circuit 2 and diagnoses the degradation of the Si operational amplifier 11 by referring to the output degradation database 4. The diagnostic unit 3 then outputs the diagnostic result of the Si operational amplifier 11 to the monitor 51. This allows operators or maintenance personnel of nuclear power plants, etc., to check the diagnostic result displayed on the monitor 51 and decide whether or not to calibrate and / or replace the measuring instrument 40. Furthermore, as described below, if the diagnostic circuit 2 is installed in a replaceable manner for the measuring instrument 40, operators can also decide to calibrate the measuring instrument 40 while replacing the diagnostic circuit 2.

[0060] The diagnostic circuit 2 is configured independently of the measuring instrument 40. For example, in this embodiment, the diagnostic circuit 2 can be mounted in a manner that allows it to be detachably attached to the housing of the measuring instrument 40. Of course, the mounting does not have to be detachable. Since the switch S1 for switching the power on / off to the measuring circuit 41 and the switch S2 for switching the power on / off to the diagnostic circuit 2 are separate, it is possible to attach the diagnostic circuit 2 to the measuring instrument 40 while continuing measurements by the measuring circuit 41. The diagnostic circuit 2 may also be mounted inside the housing of the measuring instrument 40.

[0061] <Fourth Embodiment> Next, as a fourth embodiment, the configuration of (2) described above, that is, the configuration in which the Si operational amplifier in the measuring instrument is switched between the measurement circuit and the diagnostic circuit, will be explained with reference to Figure 8. Figure 8 is a schematic diagram showing an example of the configuration of a measuring instrument that implements the diagnostic circuit of the deterioration diagnosis system according to the fourth embodiment of the present invention. As shown in Figure 8, the measuring instrument 40A, located in the high-radiation area, is connected to the central control panel 50.

[0062] The control unit 42 is, for example, a microcontroller and controls the entire measuring instrument 40, including the measuring circuit 41A. The measurement circuit 41A is a circuit including a Si operational amplifier 11t, and outputs the output signal of the Si operational amplifier 11t corresponding to the physical quantity to be measured as a measurement result via a cable to a control device (not shown) in the central control panel 50. A switch S3 is connected to the output side of the Si operational amplifier 11t. The switch S3 switches its connection destination under the control of the control unit 42. By operating the switch S3, the output signal of the Si operational amplifier 11t is output to either the central control panel 50 or the input terminal of the SiC operational amplifier 12 that constitutes the diagnostic circuit 2B.

[0063] Diagnostic circuit 2B is a configuration of diagnostic circuit 2 shown in Figure 1, but without the Si operational amplifier 11. It includes a SiC operational amplifier 12 and a subtraction circuit 10 consisting of a SiC operational amplifier 13 and resistors R1 to R4. The output signal of Si operational amplifier 11t is input to SiC operational amplifier 13 via switch S3. This corresponds to a configuration in which Si operational amplifier 11 shown in Figures 1 and 6 is replaced with Si operational amplifier 11t of measurement circuit 41A.

[0064] At least the Si operational amplifier 11t in the measurement circuit 41A and each operational amplifier in the diagnostic circuit 2B use a common power supply voltage (positive power supply V). dd , V ss The control unit 42 controls the power supply to the measurement circuit 41A by switching the switch S1 on and off, and controls the power supply to the diagnostic circuit 2B by switching the switch S2 on and off.

[0065] The diagnostic circuit 2B of the measuring instrument 40A, the diagnostic unit 3 located in the central control panel 50, and the output degradation database 4 constitute a degradation diagnostic system 1B. In this degradation diagnostic system 1B, the diagnostic unit 3 directly diagnoses the degradation of the Si operational amplifier 11t, thereby enabling the diagnosis of the degradation of the measuring circuit 41A, which has the Si operational amplifier 11t, and consequently the degradation of the measuring instrument 40A.

[0066] The measuring instrument 40A is configured so that the output signal of the Si operational amplifier 11t being diagnosed can be switched between measurement and diagnostic use via switch S3. By sharing the Si operational amplifier 11t between the measurement circuit 41A and the diagnostic circuit 2B, the measuring instrument 40A can be made smaller.

[0067] The present invention is not limited to the embodiments described above, and it goes without saying that various other modifications and applications are possible as long as they do not depart from the gist of the invention as described in the claims. For example, the embodiments described above are detailed and specific in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those comprising all the components described. Furthermore, it is possible to replace a part of the configuration of one embodiment with a component of another embodiment. It is also possible to add a component of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, replace, or delete other components for a part of the configuration of each embodiment.

[0068] Furthermore, some or all of the above configurations, functions, and processing units may be implemented in hardware, for example, by designing them as integrated circuits. Broadly defined processor devices such as FPGAs (Field Programmable Gate Arrays) and ASICs (Application Specific Integrated Circuits) may be used as hardware. [Explanation of symbols]

[0069] 1,1A,1B…Degradation diagnostic system, 2,2A,2B…Diagnostic circuit, 3…Diagnostic unit, 4…Output degradation database (DB), 10…Subtraction circuit, 11,11t…Si operational amplifier, 12,13…SiC operational amplifier, 20…Computer, 30…Subtraction unit, 40,40A…Measuring instruments, 41,41A…Measuring circuit, 42…Control unit, 50…Central control panel, 51…Monitor

Claims

1. A first operational amplifier constructed using silicon, A second operational amplifier constructed using a semiconductor with a larger band gap than silicon, A subtraction circuit that subtracts the output of the first operational amplifier from the output of the second operational amplifier, A database containing information on radiation-induced degradation of the output of operational amplifiers constructed using silicon and operational amplifiers constructed using semiconductors with a larger band gap than silicon, The diagnostic unit includes a diagnostic unit that diagnoses the degradation of the first operational amplifier based on the output of the subtraction circuit and the information registered in the database, and outputs a diagnostic result. Deterioration diagnosis system.

2. The database contains information showing the progression of a first offset voltage relative to the cumulative absorbed dose for the operational amplifier constructed using silicon, and information showing the progression of a second offset voltage relative to the cumulative absorbed dose for the operational amplifier constructed using a semiconductor with a larger band gap than silicon. The deterioration diagnosis system according to claim 1.

3. The power supply voltages of the first operational amplifier and the second operational amplifier are common. The deterioration diagnosis system according to claim 2.

4. The subtraction circuit is configured using a third operational amplifier made of a semiconductor with a larger band gap than silicon, and the power supply voltage of the third operational amplifier is common to the power supply voltages of the first operational amplifier and the second operational amplifier. The deterioration diagnosis system according to claim 3.

5. The subtraction circuit is placed in a lower radiation environment than the first and second operational amplifiers, and the subtraction circuit is configured using an integrated circuit. The deterioration diagnosis system according to claim 3.

6. The first operational amplifier is shared with the silicon-based operational amplifier implemented in the measuring instrument. The deterioration diagnosis system according to claim 1.

7. The semiconductor having a larger band gap than silicon is silicon carbide. A deterioration diagnosis system according to any one of claims 1 to 6.

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