Abnormality determination device

Abstract

To provide an abnormality determination device that can determine an abnormality in a heater without using temperature information on the heater.SOLUTION: An abnormality determination device comprises: a first calculation unit that, from a voltage detected by a voltage sensor that detects a voltage at both ends of an electric heating body and a current detected by a current sensor that detects a current flowing in the electric heating body, calculates the resistance value and the power value of the electric heating body; a second calculation unit that calculates a reference resistance value based on the resistance value and the power value; and an abnormality determination unit that determines that the heater is abnormal when the resistance value is larger than the reference resistance value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an abnormality determination device for determining an abnormality of a heater.

Background Art

[0002] Patent Document 1 discloses an electric heater that determines an abnormality of a heater based on the magnitude of a change in the rate of increase in electrical resistance during energization.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The electrical resistance of the heater wire of an electric heater has temperature characteristics. In the electric heater of Patent Document 1, since it does not include a sensor for detecting the temperature of the heater wire, it may not be possible to accurately determine the magnitude of the change in the rate of increase in electrical resistance during energization.

[0005] An object of the present disclosure is to solve the above problems and provide an abnormality determination device capable of determining an abnormality of a heater without using temperature information of the heater.

Means for Solving the Problems

[0006] To achieve the above object, an abnormality determination device according to one aspect of the present disclosure includes: a first calculation unit that calculates a resistance value and a power value of the heating element from a voltage detected by a voltage sensor that detects a voltage across both ends of the heating element of the heater and a current detected by a current sensor that detects a current flowing through the heating element; a second calculation unit that calculates a reference resistance value based on the resistance value and the power value; An abnormality determination unit that determines that the heater is abnormal when the resistance value is greater than the reference resistance value is provided.

Advantages of the Invention

[0007] According to the above aspect of the present disclosure, it is possible to determine an abnormality of the heater without using temperature information of the heater.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the drawings.

[0010] (Embodiment) An abnormality determination device 200 according to an embodiment of the present disclosure is connected to a heating wire 20 (an example of a heating element) of an electric resistance heater 2 (hereinafter simply referred to as a "heater") as shown in FIG. 1. As an example, a thermostat 100 and a solid state relay (SSR) 110, which is an example of a switching element, are connected to the heating wire 20. A power supply 120 is connected to the solid state relay 110. The solid state relay 110 is turned on and off by the thermostat 100, and the heating wire 20 is energized by the power supply 120 during the on period of the solid state relay 110.

[0011] The abnormality determination device 200 includes a voltage sensor 210, a current sensor 220, a calculation unit 240, and an abnormality determination unit 270. In this embodiment, the abnormality determination device 200 further includes an AD (analog-to-digital) converter 230, a display unit 250, and an operation unit 260.

[0012] The voltage sensor 210 detects the voltage at both ends of the heating wire 20. The analog data corresponding to the detected voltage is output to the AD converter 230.

[0013] The current sensor 220 detects the current flowing through the heating wire 20. The analog data corresponding to the current detected by the detected current sensor 220 is output to the AD converter 230.

[0014] The AD converter 230 converts the analog data corresponding to the voltage output from the voltage sensor 210 into a voltage value V which is digital data. The AD converter 230 converts the analog data corresponding to the current output from the current sensor 220 into a current value I which is digital data. The voltage value V and the current value I are output to the calculation unit 240.

[0015] The calculation unit 240 includes a CPU that performs operations, and a storage unit 246 that stores programs, data, etc. necessary for abnormality determination of the heating wire 20. The calculation unit 240 includes a first calculation unit 242 and a second calculation unit 244. The first calculation unit 242 and the second calculation unit 244 are functions realized, for example, when the CPU executes a predetermined program.

[0016] The first calculation unit 242 calculates the power value W and the resistance value R of the heating wire 20 from the voltage detected by the voltage sensor 210 and the current detected by the current sensor 220. The calculated resistance value R is output to the second calculation unit 244, the display unit 250, and the abnormality determination unit 270. Also, the power value W calculated by the first calculation unit 242 is output to the second calculation unit 244 and the display unit 250.

[0017] The second calculation unit 244 calculates a reference resistance value Rr based on the resistance value R and the power value W. In the present embodiment, the second calculation unit 244 calculates the reference resistance value Rr based on the resistance value R and the LPF output value (hereinafter referred to as the LPF output value Wf) of the power value obtained by subjecting the power value W to a first-order lag filter process (hereinafter referred to as LPF). When the LPF is f1, the Laplace operator is s, and the time constant is T1, the LPF can be represented by the calculation formula f1 = 1 / (1 + T1·s).

[0018] Specifically, when the heater 2 is in a temperature rising state, the second calculation unit 244 acquires time series data of the voltage and current detected by the voltage sensor 210 and the current sensor 220 (hereinafter referred to as the voltage and current in the temperature rising state), and calculates the resistance value R and the LPF output value Wf from the acquired time series data of the voltage and current in the temperature rising state. For example, when a first-order lag filter process corresponding to the delay time from power to temperature is performed on the power value W, it can be converted into the LPF output value Wf in which the horizontal axis X is proportional to the temperature of the heating wire 20 (see FIG. 2). It can be estimated that the LPF output value Wf obtained from the power and current in the temperature rising state and the LPF output value Wf obtained from the voltage and current detected by the voltage sensor 210 and the current sensor 220 (hereinafter referred to as the power and current at stability) when the heater 2 is in a stable state are on the same straight line or curve. In FIG. 2, the vertical axis Y represents the resistance value R, and the horizontal axis X represents the LPF output value Wf.

[0019] The temperature rising state refers to a state in which the temperature of the heating wire 20 is not maintained at the target value, and the stable state refers to a state in which the temperature of the heating wire 20 is maintained at the target value.

[0020] The second calculation unit 244 evaluates the variation in the calculated resistance value R from the time-series data of the resistance value R and the LPF output value Wf. For example, the second calculation unit 244 evaluates the sum of the squared errors from the approximate straight line L in the vertical axis Y direction in the time-series data of all the resistance values R and the LPF output values Wf as the variation in the resistance value R. The approximate straight line L is obtained, for example, using the least squares method from the time-series data of the resistance value R and the LPF output value Wf. The approximate straight line L may be a broken line composed of a plurality of straight lines by dividing the horizontal axis X into a plurality of intervals. When it is evaluated that the variation in the resistance value R is the smallest, the second calculation unit 244 calculates the approximate straight line L as the estimated temperature characteristic, and calculates the reference resistance value Rr from the calculated estimated temperature characteristic and the LPF output value Wf.

[0021] When it is evaluated that the variation in the resistance value R is not the smallest, the second calculation unit 244 re-sets the time constant T1 of the LPF, and evaluates the variation in the resistance value R from the time-series data of the resistance value R and the LPF output value Wf calculated again.

[0022] The adjustment unit 248 adjusts the time constant T1 of the LPF. The adjustment of the time constant T1 of the LPF can be performed, for example, using simulated annealing or a genetic algorithm. The adjustment of the time constant T1 of the LPF is performed by the second calculation unit 244 until it is determined that the variation in the resistance value R is the smallest.

[0023] In this embodiment, the adjustment of the time constant T1 of the LPF performs a search for the time constant T1 by setting a predetermined parameter. The predetermined parameter includes, for example, the number of searches, the time constant, the number of search points, the convergence condition, the time constant upper limit, the time constant lower limit, and the time constant width. As an example, the initial values of each parameter are set as follows. Number of searches It = 0 Time constant T1 = 0 Number of search points J = 1 Convergence condition De = 0.01 (Ω 2 ) Time constant upper limit Tma = 1000 (S) Time constant lower limit Tmi = 0 (S) Time constant width Wid = Tma - Tmi

[0024] The storage unit 246 is composed of, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), and an SSD (Solid State Drive). The storage unit 246 stores the time-series data of the power and voltage detected by the voltage sensor 210 and the current sensor 220, the power value and resistance value calculated by the first calculation unit 242, the time constant T1 of the LPF, and in addition, the LPF output value Wf and the reference resistance value Rr calculated by the second calculation unit 244.

[0025] When the LPF output value Wf of the power value W is set as X and the resistance value R is set as Y, when the curve representing the estimated temperature characteristic is approximated by the calculation formula Y = aX + b, the storage unit 246 stores the reference resistance value Rr in a form that stores two coefficients a and b.

[0026] The display unit 250 is composed of, for example, a liquid crystal display device. The display unit 250 displays the result calculated by the calculation unit 240 (for example, the graph shown in FIG. 2). The GUI (Graphical User Interface) displayed on the display unit 250 is realized by, for example, software stored in the storage unit 246 or an external device.

[0027] The operation unit 260 is composed of, for example, a key input switch or a slide switch, inputs an instruction from a user (operator), and sets the input content. In the present embodiment, the operation unit 260 is configured to be able to input, for example, the time constant T1 of the LPF.

[0028] When the resistance value R calculated by the first calculation unit 242 is larger than the reference resistance value Rr calculated by the second calculation unit 244, for example, when the resistance value R is 1.1 times or more of the reference resistance value Rr, the abnormality determination unit 270 determines that the heater 2 is abnormal. The abnormality of the heater 2 includes, for example, a state where the heating wire 20 cannot be controlled to the target temperature due to deterioration of the heating wire 20. When it is determined that the heater 2 is abnormal, the abnormality determination unit 270 outputs, for example, a signal for notifying the abnormality to the alarm device via a wireless communication device.

[0029] In this embodiment, the abnormality determination unit 270 performs an abnormality determination process when the heater 2 is in a stable state. In this case, for example, the abnormality determination unit 270 sets the upper limit value and the lower limit value of the LPF output value Wf in the stable state (hereinafter referred to as the stable range). When the LPF output value Wf is within the stable range and a preset waiting time (for example, twice the time constant T1 of the LPF) has elapsed since the LPF output value Wf entered the stable range, the abnormality determination unit 270 determines that the heater 2 is in a stable state. The abnormality determination is performed using the LPF output value Wr after it is determined that the heater 2 is in a stable state. If the LPF output value Wf goes out of the stable range before the predetermined time elapses, the measured time is reset.

[0030] Next, the abnormality determination process of the abnormality determination device 200 will be described.

[0031] As shown in FIG. 3, the voltage sensor 210 detects the voltage at both ends of the heating wire 20, and the current sensor 220 detects the current flowing through the heating wire 20 (step S11). The detected voltage and current flowing through the heating wire 20 are converted into digital data by the AD converter 230 and output to the calculation unit 240.

[0032] When the detected voltage and current are output to the calculation unit 240, the first calculation unit 242 calculates the power value W and the resistance value R from the output voltage and current (step S12).

[0033] When the power value W and the resistance value R are calculated, the second calculation unit 244 calculates a reference resistance value Rr based on the power value W (step S13).

[0034] When the reference resistance value Rr is calculated, the abnormality determination unit 270 determines whether the heater 2 is in a stable state (step S14). Step S14 is repeated until it is determined that the heater 2 is in a stable state.

[0035] When it is determined that the heater 2 is in a stable state, the abnormality determination unit 270 determines whether the resistance value R is greater than the reference resistance value Rr (step S15).

[0036] When it is determined that the resistance value R is greater than the reference resistance value Rr, the abnormality determination unit 270 determines that the heater 2 is abnormal and outputs an abnormality signal indicating that the heater 2 is abnormal (step S16).

[0037] When it is determined in step S15 that the resistance value R is less than or equal to the reference resistance value Rr, or when an abnormality signal is output in step S16, the calculation unit 240 determines whether to end the abnormality determination process (step S17). For example, when the power supply of the heater 2 is turned off, the calculation unit 240 ends the abnormality determination process. Steps S11 to S17 are repeated until it is determined that the abnormality determination process ends.

[0038] Next, the time constant adjustment process of the LPF in the second calculation unit 244 will be described.

[0039] As shown in FIG. 4, the first calculation unit 242 acquires time series data of the voltage and current in the temperature rising state (step S21).

[0040] When the time series data of the voltage and current in the temperature rising state is acquired, the first calculation unit 242 calculates the resistance value in the temperature rising state (hereinafter referred to as the temperature rising resistance value Ru) and the LPF output value Wru in the temperature rising state (hereinafter referred to as the temperature rising LPF output value Wru) from the acquired voltage and current (step S22).

[0041] When the temperature rising resistance value Ru and the temperature rising LPF output value Wru are calculated, the second calculation unit 244 performs an initial setting of parameters for adjusting the time constant T1 of the LPF (step S23).

[0042] When the initial setting of the parameters is performed, the second calculation unit 244 calculates the squared error from each time series data of the temperature rising LPF output value Wru based on the temperature rising resistance value Ru and a plurality of different time constants T1, and stores the smallest squared error (hereinafter referred to as the minimum error) among the calculated squared errors in the storage unit 246 (step S24).

[0043] When the minimum error is stored in the storage unit 246, the second calculation unit 244 determines whether the end condition is satisfied (step S25). For example, when the number of adjustment times It is 2 or more and the difference between the minimum error calculated in the previous adjustment and the minimum error calculated in the current adjustment satisfies the convergence condition De, the end condition is satisfied.

[0044] When it is determined that the end condition is satisfied, the second calculation unit 244 sets the time constant T1 when the minimum error calculated in the current adjustment is calculated as the time constant T1 of the LPF (step S27), and the time constant adjustment process of the LPF ends. The set time constant T1 is stored in the storage unit 246. When it is determined that the end condition is not satisfied, the second calculation unit 244 changes the time constant width, the time constant upper limit, and the time constant lower limit among the parameters from the set values (step S26). When the parameters are changed, the number of adjustment times is incremented by 1, and the minimum error is calculated again in step S24.

[0045] According to the abnormality determination device 200, when the resistance value of the heating wire 20 is larger than the reference resistance value Rr calculated based on the resistance value of the heating wire 20 and the LPF output value Wr of the power value of the heating wire 20, the abnormality determination unit 270 determines that the heater 2 is abnormal. With such a configuration, it is possible to determine the abnormality of the heater 2 without using the temperature information of the heating wire 20 of the heater 2.

[0046] The second calculation unit 244 calculates the reference resistance value Rr based on the estimated temperature characteristic calculated based on the LPF output value Wf and the resistance value R and the LPF output value Wf. With such a configuration, it is possible to more reliably determine the abnormality of the heater 2 without using the temperature information of the heating wire 20 of the heater 2.

[0047] The filter process is a first-order lag filter process. With such a configuration, it is possible to determine the abnormality of the heater 2 with a simple configuration without using the temperature information of the heating wire 20 of the heater 2.

[0048] The abnormality determination device 200 includes an operation unit 260 and a display unit 250. With such a configuration, for example, the user can manually input the time constant T1 of the LPF.

[0049] The abnormality determination device 200 includes a storage unit 246 that stores a reference resistance value Rr. With such a configuration, it is not necessary to calculate the reference resistance value Rr every time an abnormality is determined, and the processing load on the calculation unit 240 can be reduced.

[0050] When the storage unit 246 sets the power value as X and the resistance value as Y, when the expression representing the estimated temperature characteristic is approximated by the calculation formula Y = aX + b, the storage unit 246 stores the reference resistance value Rr in a form that stores the coefficients a and b of the calculation formula. With such a configuration, it is not necessary to comprehensively store the combination of the LPF output value Wf and the reference resistance value Rr, so the capacity of the data stored in the storage unit 246 can be suppressed.

[0051] The abnormality determination unit 270 determines whether the heater 2 is abnormal after the LPF output value is within the stable range and after a preset waiting time has elapsed since the LPF output value entered the stable range. With such a configuration, the abnormality of the heater 2 can be determined more accurately.

[0052] In this embodiment, the filter processing in the second calculation unit 244 is a first-order lag filter processing, but the filter processing is not limited to this. The filter processing may be, for example, a second-order lag filter processing. When the second-order lag filter is f2, the Laplace operator is s, and the time constants are T1 and T2, the second-order lag filter can be represented by the calculation formula f2 = 1 / {(1 + T1·s)·(1 + T2·s)}. At this time, when the LPF output value of the power value W is X and the resistance value R is Y, the curve representing the estimated temperature characteristic is the calculation formula Y = aX 2It is approximated by +bX + c. In this case, the storage unit 246 can store the reference resistance value Rr in a form that stores the three coefficients a, b, and c. Even when performing the second-order lag filter process, it is possible to determine the abnormality of the heater 2 with a simple configuration without using the temperature information of the heating wire 20 of the heater 2. Also, the capacity of the data stored in the storage unit 246 can be suppressed.

[0053] In the present embodiment, the operation unit 260 may be configured to be able to input not only the time constant but also other parameters or control contents.

[0054] In the present embodiment, the operation unit 260 is configured by a key input switch or a slide switch or the like, but the means by which the user (operator) sets the input content for the second calculation unit 244 is not limited to this. The means by which the user (operator) sets the input content for the second calculation unit 244 may be recorded, for example, as software (computer program) on a non-transitory recording medium such as a CD (compact disc), a DVD (digital versatile disc), or a flash memory that can store data. By installing the software recorded on such a recording medium in a substantial computer device such as a personal computer, a PDA (personal digital assistant), a smartphone, or a PLC (programmable logic controller), the above-described means by which the user (operator) sets the input content for the second calculation unit 244 can be executed on those computer devices.

[0055] In the present embodiment, the case where the second calculation unit 244 automatically adjusts the time constant T1 of the LPF has been described, but the means for adjusting the time constant T1 of the LPF is not limited to this. After the second calculation unit 244 performs an exploratory adjustment of the time constant T1 of the LPF, the user (operator) may input the value of the time constant T1 by operating the operation unit 260 while looking at the display unit 250. By doing so, the value of the time constant T1 of the LPF can be finely adjusted.

[0056] In this embodiment, the abnormality determination unit 270 may be configured to perform an abnormality determination not only when the heater 2 is in a stable state but also when the heater 2 is in a temperature rising state. In this case, in the flowchart of FIG. 3, step S14 is omitted.

[0057] In this embodiment, the abnormality determination device 200 includes a voltage sensor 210, a current sensor 220, a calculation unit 240, and an abnormality determination unit 270. However, the configuration of the abnormality determination device 200 is not limited to this. The voltage sensor 210 and the current sensor 220 can be omitted. For example, the abnormality determination device 200 may be configured integrally with the voltage sensor 210 and the current sensor 220, or may be configured separately from the voltage sensor 210 and the current sensor 220. When configured separately from the voltage sensor 210 and the current sensor 220, the abnormality determination unit 270 may be provided in an external device such as a server, and various data may be input and output to each other via a wireless communication device.

[0058] The above embodiments are illustrative, and various modifications can be made without departing from the scope of the present invention.

[0059] As described above, various embodiments in the present disclosure have been described in detail with reference to the drawings. Finally, various aspects of the present disclosure will be described. In the following description, as an example, reference numerals are also attached.

[0060] The abnormality determination device 200 according to the first aspect of the present disclosure a first calculation unit 242 that calculates a resistance value R and a power value W of the heating element from the voltage detected by a voltage sensor 210 that detects the voltage across both ends of the heating element of the heater 2 and the current detected by a current sensor 220 that detects the current flowing through the heating element; a second calculation unit 244 that calculates a reference resistance value Rr based on the resistance value R and the power value W; an abnormality determination unit 270 that determines that the heater 2 is abnormal when the resistance value R is greater than the reference resistance value Rr and.

[0061] The abnormality determination device 200 according to the second aspect of the present disclosure is, The second calculation unit 244 calculates a reference resistance value Rr based on the estimated temperature characteristics calculated based on the filtered power value W and the resistance value R, and the filtered power value W.

[0062] The abnormality determination device 200 according to the third aspect of the present disclosure is, The filtering process is a first-order lag filtering process.

[0063] The abnormality determination device 200 according to the fourth aspect of the present disclosure is, The filtering process is a second-order lag filtering process.

[0064] The abnormality determination device 200 according to the fifth aspect of the present disclosure is, The second calculation unit 244 sets the time constant of the filtering process so that the variation in the resistance value R in the estimated temperature characteristics is minimized.

[0065] The abnormality determination device 200 according to the sixth aspect of the present disclosure is, a voltage sensor 210, a current sensor 220, an operation unit 260 capable of inputting the time constant, and a display unit 250 that displays the resistance value R and the filtered power value Wf. and includes.

[0066] The abnormality determination device 200 according to the seventh aspect of the present disclosure is, and includes a storage unit 246 that stores the reference resistance value Rr calculated by the second calculation unit 244.

[0067] The abnormality determination device 200 according to the eighth aspect of the present disclosure is, When the storage unit 246 stores the two coefficients a and b in a form such that the curve representing the estimated temperature characteristics is approximated by the calculation formula Y = aX + b, where the filtered power value Wf is X and the resistance value R is Y, the storage unit 246 stores the reference resistance value Rr. When the filtered power value Wf is X and the resistance value R is Y, Y = aX + b When the curve representing the estimated temperature characteristics is approximated by the calculation formula, the reference resistance value Rr is stored in a form that stores the two coefficients a and b.

[0068] The abnormality determination device 200 according to the ninth aspect of the present disclosure is The storage unit 246 is When the power value Wf subjected to the filter process is X and the resistance value R is Y, Y = aX 2 + bX + c When the curve representing the estimated temperature characteristic is approximated by the calculation formula, the reference resistance value Rr is stored in a form in which three coefficients a, b, and c are stored.

[0069] The abnormality determination device 200 according to the tenth aspect of the present disclosure is The abnormality determination unit 270 is Set the stable range of the power value Wf subjected to the filter process, After the power value Wf subjected to the filter process is within the stable range and a preset waiting time has elapsed since the power value Wf subjected to the filter process entered the stable range, it is determined whether the heater 2 is abnormal.

Industrial Applicability

[0070] The abnormality determination device according to the above aspect of the present invention is applicable to abnormality determination of electric heaters, and also to heating elements that generate heat by resistance heating such as fuses, conductive wires, or transmission lines.

Explanation of Signs

[0071] 2 Heater 20 Heating wire 100 Thermostat 110 Solid state relay 120 Power supply 200 Abnormality determination device 210 Voltage sensor 220 Current sensor 230 AD converter 240 Calculation unit 242 First calculation unit 244 Second calculation unit 246 Storage unit 248 Adjustment unit 250 Display unit 260 Operation unit 270 Abnormality determination unit

Claims

1. A first calculation unit that calculates a resistance value and a power value of the heating element from a voltage detected by a voltage sensor that detects a voltage at both ends of the heating element of the heater and a current detected by a current sensor that detects a current flowing through the heating element; A second calculation unit that calculates a reference resistance value based on the resistance value and the power value; An abnormality determination unit that determines that the heater is abnormal when the resistance value is greater than the reference resistance value; and the second calculation unit calculates the reference resistance value based on an estimated temperature characteristic calculated based on the power value and the resistance value subjected to filter processing and the power value subjected to the filter processing, the filter processing is a first-order lag filter processing, an abnormality determination device.

2. A first calculation unit that calculates a resistance value and a power value of the heating element from a voltage detected by a voltage sensor that detects a voltage at both ends of the heating element of the heater and a current detected by a current sensor that detects a current flowing through the heating element; A second calculation unit that calculates a reference resistance value based on the resistance value and the power value; An abnormality determination unit that determines that the heater is abnormal when the resistance value is greater than the reference resistance value; and the second calculation unit calculates the reference resistance value based on an estimated temperature characteristic calculated based on the power value and the resistance value subjected to filter processing and the power value subjected to the filter processing, the filter processing is a second-order lag filter processing, an abnormality determination device.

3. The abnormality determination device according to claim 1 or 2, wherein the second calculation unit sets a time constant of the filter processing so that a variation in the resistance value in the estimated temperature characteristic is minimized.

4. the voltage sensor; the current sensor; an operation unit capable of inputting the time constant; A display unit that displays the resistance value and the power value subjected to the filtering process The abnormality determination device according to claim 3, comprising:

5. The abnormality determination device according to any one of claims 1 to 3, further comprising a storage unit that stores the reference resistance value calculated by the second calculation unit.

6. The storage unit When the power value subjected to the filtering process is X and the resistance value is Y Y = aX + b The abnormality determination device according to claim 5, wherein when a curve representing the estimated temperature characteristic is approximated by a calculation formula of Y = aX + b, the reference resistance value is stored in a form that stores two coefficients a and b.

7. The storage unit When the power value subjected to the filtering process is X and the resistance value is Y Y = aX2 + bX + c The abnormality determination device according to claim 5, wherein when a curve representing the estimated temperature characteristic is approximated by a calculation formula of Y = aX2 + bX + c, the reference resistance value is stored in a form that stores three coefficients a, b, and c.

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