Measurement system

Abstract

We provide a measurement system that operates appropriately even in a radiation environment. [Solution] The measurement system 1 is provided with a selection unit 44 that selects one of the signal sources 10 by turning on one of the analog switches 22 of the multiplexer 20; a first measurement unit 50 that terminates a pair of signal lines 32 with a first impedance R1 and measures a first signal I1 supplied via the pair of signal lines 32; a second measurement unit 60 that terminates a pair of signal lines 32 with a second impedance R2 and measures a second signal I2 supplied via the pair of signal lines 32; and a correction unit 70 that corrects measurement errors due to leakage current leaking from the multiplexer 20 based on the measurement results of the first measurement unit 50 and the second measurement unit 60.

Description

Technical Field

[0001] The present invention relates to a measurement system.

Background Art

[0002] In recent years, various inspections and measurements such as temperature, water level, pressure, and radiation have been required for condition monitoring and condition grasping of plants and equipment. Along with this, the number of installed measuring instruments has been increasing, and reduction of the number of cables is desired. For example, in the claims of Patent Document 1 below, "a first multiplexer that switches and captures minute voltages corresponding to the measured temperatures of a plurality of thermocouples, an amplifier that amplifies the minute voltages, an analog-to-digital converter that converts the voltage amplified by this amplifier into a digital value, a corrector that corrects the signal of the digital value according to the ambient temperature and type of each of the thermocouples, and a second multiplexer that sequentially switches and supplies a direct-current minute current to each of the thermocouples via a high resistance for disconnection detection." is described.

[0003] Also, in the summary of Patent Document 2 below, "A multi-input / output (I / O) system detects leakage current in a selected input channel. The system includes a leakage current detection multiplexer connected to supply an output selected from one of a plurality of input channels. Further, the leakage detection multiplexer supplies the leakage current measured for the selected input channel as part of the output. Based on the detected leakage current, it is possible to perform a measurement on whether the detected leakage current has caused loss of integrity of the output of the multiplexer. Furthermore, the detected leakage current is used to correct the output supplied by the multiplexer and can compensate for the presence of leakage current in the selected channel." is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] By the way, in the technology described above, if the multiplexer is placed in a radiation environment, the semiconductor elements will deteriorate due to radiation exposure, and eventually the multiplexer will cease to function properly. This invention was made in view of the circumstances described above, and aims to provide a measurement system that operates appropriately even in a radiation environment. [Means for solving the problem]

[0006] To solve the above problems, the present invention provides a measurement system comprising: a multiplexer having a plurality of analog switches, each having one end connected to a plurality of signal sources and each having a semiconductor with a bandgap larger than silicon; and a measurement device connected to the other ends of the plurality of analog switches via a pair of signal lines, wherein the measurement device comprises: a selection unit that selects one of the signal sources by turning on one of the analog switches of the multiplexer; a first measurement unit that terminates the pair of signal lines with a first impedance and measures a first signal supplied via the pair of signal lines; a second measurement unit that terminates the pair of signal lines with a second impedance and measures a second signal supplied via the pair of signal lines; and a correction unit that corrects measurement errors due to leakage current leaking from the multiplexer based on the measurement results of the first and second measurement units. [Effects of the Invention]

[0007] The measurement system of the present invention operates appropriately even in a radiation environment. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram showing the configuration of the measurement system according to the first embodiment. [Figure 2] This figure shows an example of the terminal voltage measured by the first measurement unit of a comparative example. [Figure 3] This figure shows an example of the terminal voltage measured by the first measurement unit of another comparative example. [Figure 4] This is a diagram showing the configuration of the measurement system according to the second embodiment. [Figure 5] This is a block diagram of a computer. [Modes for carrying out the invention]

[0009] [Summary of the Embodiment] In devices such as multiplexers, which are constructed using semiconductor elements, the semiconductor elements degrade due to radiation exposure, making them difficult to use, especially in high-radiation environments. One of the radiation-related failure factors in these devices is that if the circuit includes MOSFETs, the ionizing effect of radiation can cause charge accumulation, preventing the MOSFETs from functioning properly.

[0010] One effective method for ensuring the normal operation of electronic circuits in a radiation environment is to replace MOSFETs from conventional silicon (Si) to elements with superior radiation resistance, such as silicon carbide (SiC), gallium nitride (GaN), or diamond semiconductors. For example, by constructing an electronic circuit with SiC, it is possible to improve radiation resistance by more than three orders of magnitude compared to conventional Si elements.

[0011] As described above, radiation resistance can be improved by constructing MOSFETs and multiplexers with integrated MOSFETs from SiC. However, our tests have revealed that even with SiC, leakage current gradually increases if radiation exposure continues. For example, when used in high-radiation environments such as inside the PCV (reactor containment vessel) of a nuclear power plant or during an accident, further countermeasures may be necessary.

[0012] Therefore, in the embodiment described later, measurement errors due to leakage current of a multiplexer made of SiC or the like are reduced. This makes it possible to realize a radiation-hardened multiplexer measurement system that can perform high-precision measurements over a long period of time even in high-radiation environments.

[0013] [First Embodiment] <Configuration of the first embodiment> (Overall structure) Figure 1 is a diagram showing the configuration of the measurement system 1 according to the first embodiment. The measurement system 1 comprises thermocouples 10-1 to 10-N (signal sources) with N circuits (where N is multiple), a pair of multiplexers 20-A and 20-B, signal lines 32-A and 32-B, control lines 34-A and 34-B, and a measuring device 40. In the following description, multiple components, physical quantities, information, etc., having the same or similar function or significance may be represented by adding a hyphen and alphanumeric characters to the same symbol, such as "thermocouple 10-1 to 10-N". However, if it is not necessary to distinguish between these multiple components, etc., the hyphen and alphanumeric characters may be omitted, such as "thermocouple 10".

[0014] The multiplexer 20-A comprises analog switches 22-A1 to 22-AN with a number of circuits N, and a control circuit 24-A. One end of each analog switch 22-A1 to 22-AN is connected to one end of each thermocouple 10-1 to 10-N, and the other end of each analog switch 22-A1 to 22-AN is connected to the signal line 32-A. The control circuit 24-A receives a selection signal SX from the measuring device 40. This selection signal SX specifies the thermocouple number k (where 1 ≤ k ≤ N). Based on the selection signal SX received from the measuring device 40, the control circuit 24-A exclusively turns on the analog switch 22-Ak corresponding to the thermocouple number k among the analog switches 22-A1 to 22-AN.

[0015] Similarly, the multiplexer 20-B includes analog switches 22-B1 to 22-BN with the number of circuits N and a control circuit 24-B. One end of each of the analog switches 22-B1 to 22-BN is connected to the other end of each of the thermocouples 10-1 to 10-N, and the other end of each of the analog switches 22-B1 to 22-BN is connected to the signal line 32-B.

[0016] Based on the selection signal SX described above, the control circuit 24-B exclusively turns on the analog switch 22-Bk corresponding to the thermocouple number k among the analog switches 22-B1 to 22-BN. As a result, at a certain timing, the thermocouple 10-k specified by the thermocouple number k is connected to the measuring device 40 via the analog switches 22-Ak, 22-Bk and the signal lines 32-A, 32-B.

[0017] (Measuring device 40) The measuring device 40 includes switches 42-A, 42-B, a selection unit 44, a first measuring unit 50, a second measuring unit 60, and a correction unit 70. The switches 42-A, 42-B are interlocked to switch and connect the signal lines 32-A, 32-B to one of the first measuring unit 50 or the second measuring unit 60. The selection unit 44 outputs the selection signal SX described above. The selection signal SX, for example, cyclically specifies the thermocouple number k described above within the range of "1" to "N" at a predetermined period.

[0018] The first measuring unit 50 includes a resistor 54 connected between input terminals and a voltage sensor 52 that measures the terminal voltage V1 of the resistor 54. Let the resistance value of the resistor 54 be R1 (the first impedance), and the current flowing through the resistor 54 be I1 (the first signal). Note that the current I1 is equal to V1 / R1. The resistance value R1 is a resistance value within the range recommended by the manufacturer of the thermocouple 10 as the shunt resistance value of the thermocouple 10, and is, for example, about 10 to 300 Ω.

[0019] The second measuring unit 60 includes a resistor 64 connected between the input terminals and a voltage sensor 62 for measuring the terminal voltage V2 of the resistor 64. The resistance value of the resistor 64 is R2 (second impedance), and the current flowing through the resistor 64 is I2 (second signal). Note that the current I2 is equal to V2 / R2. The resistance value R2 is a different value from the resistance value R1, and it is preferable to make it about "1 / 10" of the resistance value R1, for example.

[0020] In environments where radiation can be ignored, the temperature at the thermocouple 10 can be immediately determined based on the measurement result of the current I1 at the first measurement unit 50. However, as will be described in detail later, in high-radiation environments, a problem arises in which the error in the current I1 becomes large. The correction unit 70 corrects the current I1 based on the current I2, thereby determining the temperature at the thermocouple 10 with high accuracy.

[0021] (Multiplexer 20) The analog switch 22 and control circuit 24 included in the multiplexer 20 both utilize SiC semiconductor MOSFETs, i.e., SiC-MOSFETs. However, instead of SiC-MOSFETs, MOSFETs with a wider bandgap than silicon, such as GaN (gallium nitride) or diamond semiconductor MOSFETs, may be used in the multiplexer 20.

[0022] Each analog switch 22 consists of a pair of MOSFETs connected in antiparallel between the corresponding thermocouple 10 and the signal line 32. That is, the source terminal of one MOSFET is connected to the drain terminal of the other, and the drain terminal of the other is connected to the source terminal of the other. The on / off state of the analog switch 22 is determined according to the gate voltage of the pair of MOSFETs. Each analog switch 22 can achieve operation close to that of an ideal analog switch in the initial stages of operation when the radiation exposure level is still low. That is, the on-resistance of each MOSFET is low enough to be considered "0", and the leakage current flowing from the gate terminal to the source terminal or drain terminal is also low enough to be considered "0".

[0023] However, when SiC semiconductors are 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. Although this effect is smaller in SiC semiconductors compared to Si (silicon) semiconductors, the inventors have newly discovered that the leakage current of the analog switches 22 gradually increases as radiation irradiation continues. As a result, the leakage current of each analog switch 22 causes a significant error in the temperature measurement result in the first measurement unit 50.

[0024] <Comparative Example #1> Next, before describing the operation of the first embodiment, various comparative examples will be explained. First, Comparative Example #1 will be described. The overall configuration of Comparative Example #1 is the same as that of the first embodiment (see Figure 1), but the following points differ. First, the measuring device 40 in Comparative Example #1 does not have a switch 42, a second measuring unit 60, and a correction unit 70, and the signal line 32 is directly connected to the first measuring unit 50. Also, the circuit configuration of the multiplexer 20 is the same as that of the first embodiment, but the analog switch 22 and the control circuit 24 are made of Si (silicon) semiconductors.

[0025] Figure 2 shows an example of the terminal voltage V1 measured by the first measurement unit 50 of Comparative Example #1. The terminal voltage V1s in Figure 2 is an example of the terminal voltage V1 applied to the first measurement unit 50 at the start of operation of the measurement system 1. Here, the number of circuits N in the thermocouple 10 and multiplexer 20 is assumed to be "4". When the thermocouple number k is cyclically switched in the order of "1" to "4", the output voltages of thermocouples 10-1 to 10-4 appear as the terminal voltage V1. In the example shown, the terminal voltage V1 changes in a step-like waveform.

[0026] Furthermore, the terminal voltage V1a in Figure 2 is an example of the terminal voltage V1 after radiation exposure. When radiation is applied, the control circuit 24 that controls the analog switch 22 in the multiplexer 20 malfunctions due to charge accumulation, preventing the switching signal to the analog switch from being transmitted correctly. As a result, the output of the multiplexer 20 becomes fixed at either the ground level or the output voltage of the thermocouple 10-1 to 10-4. When this phenomenon occurs, the switching operation of the multiplexer 20 becomes impossible, and the multiplexer 20 is judged to have malfunctioned.

[0027] <Comparative Example #2> Next, Comparative Example #2 will be described. The overall configuration of Comparative Example #2 is the same as that of Comparative Example #1. That is, in Comparative Example #2 as well, the measuring device 40 does not include a switch 42, a second measuring unit 60, and a correction unit 70, and the signal line 32 is directly connected to the first measuring unit 50. However, Comparative Example #2 differs from Comparative Example #1 in that the multiplexer 20 is made of SiC semiconductor, similar to that of the first embodiment.

[0028] Figure 3 shows an example of the terminal voltage V1 measured by the first measurement unit 50 of Comparative Example #2. The terminal voltage V1s in Figure 3 is an example of the terminal voltage V1 at the first measurement unit 50 at the start of operation, and has a waveform similar to that shown in Figure 2. The terminal voltage V1b in Figure 3 is an example of the terminal voltage V1 after radiation irradiation.

[0029] When irradiated with radiation, charge accumulates in the analog switch 22 and control circuit 24 of the multiplexer 20. However, SiC semiconductors, which are wide-bandgap semiconductors, are less susceptible to adverse effects from charge accumulation (such as induction of interface defects). In addition, their leakage current is more than three orders of magnitude lower than that of Si semiconductors. Since the control circuit 24 is a digital circuit that only needs to be able to distinguish between "0" and "1", the control circuit 24 is unlikely to fail. For this reason, the example shown in Figure 3 assumes that the control circuit 24 has not failed.

[0030] On the other hand, since the analog switch 22 is supplied with current from the thermocouple 10, which is an analog signal, even a small leakage current can affect the error in the terminal voltage V1, which is the sensor's measured value. In particular, as radiation continues to irradiate and the leakage current increases, the error becomes significant. In the example in Figure 3, the terminal voltage V1b, which is the normal output terminal voltage V1s superimposed with the effect of the leakage current, appears as the terminal voltage V1.

[0031] <Operation of the First Embodiment> Next, the operation of the first embodiment will be described. First, the correction unit 70 sets switch 42 to the first measurement unit 50 side. If Vt is the thermoelectric force of thermocouple 10-k at a certain thermocouple number k, and Im is the total leakage current generated in analog switches 22-Ak and 22-Bk, then the current I1 flowing through resistor 54 is given by equation (1) below. I1 = (Vt / R1) + Im …(1)

[0032] Next, the correction unit 70 switches the switch 42 to the second measurement unit 60. The current I2 flowing through the resistor 64 corresponding to the thermocouple number k is given by equation (2) below.

[0033] I2 = (Vt / R2) + Im …(2) The correction unit 70 calculates the leakage current Im corresponding to each thermocouple number k based on the simultaneous equations (1) and (2). Once the leakage current Im is calculated, it is assumed that its value will remain almost constant for a certain period of time (several hours or several days). Therefore, during that period, the correction unit 70 continues to calculate the thermoelectric power Vt using "Vt = R1(I1-Im)" while the first measurement unit 50 is selected by the switch 42. Furthermore, the correction unit 70 outputs the temperature measurement result at each thermocouple 10-k to the outside based on the thermoelectric power Vt corresponding to each thermocouple number k. This makes it possible to obtain accurate temperature measurement results for a long period of time, even when a leakage current occurs in the analog switch 22 in a radiation environment.

[0034] [Second Embodiment] Figure 4 is a diagram showing the configuration of the measurement system 2 according to the second embodiment. In the description of each embodiment, parts corresponding to parts of the other embodiments described above are denoted by the same reference numerals, and their descriptions may be omitted. Measurement system 2 has the same components as measurement system 1 of the first embodiment, and furthermore, the measurement device 40 includes a resistance measurement unit 80. Switches 42-A and 42-B switch in conjunction to connect signal lines 32-A and 32-B to either the first measurement unit 50, the second measurement unit 60, or the resistance measurement unit 80.

[0035] The resistance measurement unit 80 includes a DC power supply 82 that applies a DC voltage to signal lines 32-A and 32-B, and a current sensor 84 that measures the current flowing through the DC power supply 82. At the start of operation of the measurement system 2, the on-resistance value of each analog switch 22 is low enough to be considered "0". However, it has been confirmed that when the analog switch 22 is irradiated with radiation, the on-resistance value also increases slightly. If the effect of this on-resistance value is large enough not to be ignored, it is preferable to compensate for the effect of the on-resistance value. Therefore, the resistance measurement unit 80 is provided to compensate for this effect of the on-resistance value.

[0036] When the measurement system 2 starts operation, the correction unit 70 connects the signal lines 32-A and 32-B to the resistance measurement unit 80. The correction unit 70 then measures the resistance value between the signal lines 32-A and 32-B corresponding to each thermocouple number k, based on the output voltage of the DC power supply 82 and the measurement result of the current sensor 84. These resistance values ​​measured at the start of operation can be considered equal to the internal resistance of each thermocouple 10-k.

[0037] Even after the operation of the measurement system 2 has started, the correction unit 70 uses the resistance measurement unit 80 to measure the resistance between signal lines 32-A and 32-B corresponding to each thermocouple number k, as needed. The result of subtracting the resistance measured at the start of operation from the resistance measured after the start of operation is considered to be the total on-resistance of analog switches 22-Ak and 22-Bk corresponding to thermocouple number k.

[0038] If Ra is the total on-resistance of analog switches 22-Ak and 22-Bk, then equations (1) and (2) above can be transformed into equations (3) and (4) below. I1 = (Vt / (R1 + Ra)) + Im …(3) I2 = (Vt / (R2 + Ra)) + Im …(4)

[0039] In the second embodiment, the correction unit 70 calculates the leakage current Im by solving the simultaneous equations (3) and (4). Then, during the period in which the leakage current Im and the on-resistance value Ra are expected to be maintained, the correction unit 70 continues to calculate the thermoelectric power Vt using the formula "Vt=(R1+Ra)(I1-Im)" while the first measurement unit 50 is selected by the switch 42. The operation of the second embodiment other than that described above is the same as that of the first embodiment. According to the second embodiment, even when leakage current and on-resistance values ​​occur in the analog switch 22 in a radiation environment, accurate temperature measurement results can be obtained over a long period of time.

[0040] [Computer Configuration] Figure 5 is a block diagram of the computer 980. The correction unit 70 shown in Figures 1 and 4 each includes one or more computers 980 as shown in Figure 5. In Figure 5, the computer 980 comprises a CPU 981, a memory unit 982, a communication port 983, an input / output port 984, and a media port 985. Here, the memory unit 982 comprises a RAM 982a, a ROM 982b, and an SSD (Solid State Drive) 982c.

[0041] The communication port 983 is connected to the communication circuit 986. The input / output port 984 is connected to the input / output device 987. The media port 985 reads and writes data to the recording medium 988. The ROM 982b stores the IPL (Initial Program Loader) and other programs executed by the CPU. The SSD 982c stores control programs and various data. The CPU 981 implements various functions by executing the control programs and other programs read from the SSD 982c into the RAM 982a.

[0042] [Differentiation] The present invention is not limited to the embodiments described above, and various modifications are possible. The embodiments described above are illustrative examples provided to facilitate understanding of the present invention, and are not necessarily limited to those comprising all the described configurations. For example, the contents of the illustrations can be changed from the actual configuration to the extent that the spirit of the present invention is not impaired, for illustrative purposes. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add a configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to delete a part of the configuration of each embodiment, or to add or replace other configurations. Furthermore, the control lines and information lines shown in the figures are those considered necessary for explanation, and do not necessarily represent all the control lines and information lines required in the product. In reality, it can be assumed that almost all configurations are interconnected. Possible modifications to the above embodiments are as follows, for example.

[0043] (1) In each of the above embodiments, a thermocouple 10 was used as an example of a signal source. However, the signal source is not limited to a thermocouple 10, and may be any other type of sensor, or a signal source that outputs an electrical signal other than a sensor.

[0044] (2) Since the hardware of the correction unit 70 in the above embodiment can be implemented by a general computer, the program that performs the various processes described above may be stored in a storage medium (a computer-readable recording medium on which the program is recorded) or distributed via a transmission line.

[0045] (3) Although the various processes described above were explained as software processes using a program in the above embodiment, some or all of them may be replaced with hardware processes using an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), etc.

[0046] (4) The various processes performed in the above embodiment may be performed by a server computer via a network (not shown), and the various data stored in the above embodiment may also be stored on the server computer.

[0047] [Effects of the Embodiment] As described above, according to each embodiment, the measuring device 40 includes a selection unit 44 that selects one of the signal sources (10) by turning on one of the analog switches 22 of the multiplexer 20; a first measuring unit 50 that terminates a pair of signal lines 32 with a first impedance (R1) and measures a first signal (I1) supplied via the pair of signal lines 32; a second measuring unit 60 that terminates a pair of signal lines 32 with a second impedance (R2) and measures a second signal (I2) supplied via the pair of signal lines 32; and a correction unit 70 that corrects measurement errors due to leakage current leaking from the multiplexer 20 based on the measurement results of the first measuring unit 50 and the second measuring unit 60. This allows the measuring systems 1 and 2 to operate properly for a long time, even when leakage current occurs in a radiation environment. In other words, accurate measurement results can be provided stably.

[0048] Furthermore, it is even more preferable that the multiplexer 20 further includes a control circuit 24 having a SiC semiconductor, which controls the on / off state of the multiple analog switches 22 in accordance with the selection signal SX supplied from the selection unit 44, provided that the multiple analog switches 22 have SiC semiconductors. This allows the on / off state of the analog switches 22 to be set by the selection unit 44 provided in the measuring device 40.

[0049] Furthermore, as in the second embodiment, it is even more preferable that the measuring device 40 further includes a resistance measuring unit 80 for measuring the resistance value between a pair of signal lines 32, and that the correction unit 70 corrects the measurement error due to leakage current based on the measurement results of the first measuring unit 50, the second measuring unit 60, and the resistance measuring unit 80. This allows the measurement error due to leakage current to be corrected by also taking into account the measurement result of the resistance measuring unit 80.

[0050] Furthermore, as in the second embodiment, it is even more preferable that the correction unit 70 measures the internal resistance of the analog switch 22 based on the change in the resistance value measured by the resistance measurement unit 80 over time. This allows for correction of measurement errors based on the measured internal resistance. [Explanation of Symbols]

[0051] 1,2 Measurement System 10 Thermocouple (signal source) 20 Multiplexer 22 Analog Switches 24 Control circuits 32 signal lines 40 Measuring devices 44 Selection Section 50 First measurement unit 60 Second measurement unit 70 Correction section 80 Resistance Measurement Section I1 Current (First signal) I2 Current (Second signal) R1 Resistance value (first impedance) R2 Resistance value (second impedance) SX selection signal

Claims

1. A multiplexer comprising multiple analog switches, each having one end connected to multiple signal sources and each having a semiconductor with a larger bandgap than silicon, A measuring device connected to the other end of a plurality of analog switches via a pair of signal lines, The aforementioned measuring device is A selection unit that selects one of the signal sources by turning on one of the analog switches of the multiplexer, A first measuring unit terminates a pair of signal lines with a first impedance and measures the first signal supplied through the pair of signal lines, A second measuring unit terminates the pair of signal lines with a second impedance and measures the second signal supplied through the pair of signal lines, The system includes a correction unit that corrects measurement errors caused by leakage current leaking from the multiplexer based on the measurement results of the first and second measurement units. A measurement system characterized by the following features.

2. The plurality of analog switches have SiC semiconductors, The multiplexer further includes a control circuit having a SiC semiconductor that controls the on / off state of a plurality of analog switches in accordance with selection signals supplied from the selection unit. The measurement system according to feature 1.

3. The system further includes a resistance measuring unit for measuring the resistance between a pair of signal lines, The correction unit corrects the measurement error caused by the leakage current based on the measurement results of the first measurement unit, the second measurement unit, and the resistance measurement unit. The measurement system according to claim 2.

4. The correction unit measures the internal resistance of the analog switch based on the change in the resistance value measured by the resistance measurement unit over time. The measurement system according to claim 3.

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