Measurement value calculation method, measurement value calculation program, and measurement value calculation device

Abstract

To provide a measurement value calculation method, a measurement value calculation program, and a measurement value calculation device capable of reducing an error between a value obtained by subtracting an offset from a signal to which the offset is applied and an original input signal.SOLUTION: A measurement value calculation method includes: generating an offset signal by performing analog conversion on an offset setting value; generating an addition signal by adding an input signal and the offset signal; calculating an addition value by performing digital conversion on the addition signal; calculating an offset conversion value by performing digital conversion on the offset signal; and calculating a measurement value by adding the offset conversion value to the addition value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a measurement value calculation method, a measurement value calculation program, and a measurement value calculation device. [Background technology]

[0002] Conventionally, a circuit is known in which the output of a D / A converter is input to an adder and an offset is applied to the adder (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 57-168075 Summary of the Invention [Problem to be solved by the invention]

[0004] After applying an offset to an input signal, the offset may be subtracted from the offset signal to calculate a value corresponding to the original input signal. When applying an offset to an input signal using a D / A converter, there is a delay in the output of the D / A converter, which causes a delay time until the offset setting is reflected. As a result, an error occurs between the value calculated by subtracting the offset from the offset signal and the original input signal.

[0005] The present disclosure has been made in consideration of the above points, and aims to provide a measurement value calculation method, a measurement value calculation program, and a measurement value calculation device that can reduce the error between the value obtained by subtracting the offset from the offset signal and the original input signal. [Means for solving the problem]

[0006] (1) A measurement value calculation method according to some embodiments includes: generating an offset signal by analog converting an offset setting value; generating a sum signal by adding an input signal and the offset signal; calculating a sum value by digital converting the sum signal; calculating an offset conversion value by digital converting the offset signal; and calculating a measurement value from the sum value and the offset conversion value. By calculating the measurement value using the offset conversion value, errors in the measurement value are reduced regardless of delays in the output response of the D / A converter when the offset setting value is changed.

[0007] (2) The measurement value calculation method of (1) above may further include switching a switch that inputs either the sum signal or the offset signal to an A / D converter, and calculating the sum value and the offset conversion value using the A / D converter. By using a switch to calculate the offset conversion value, the cost of the device can be reduced.

[0008] (3) The measurement value calculation method of (2) above may further include setting the time for switching the switch based on the output characteristics of a D / A converter that converts the offset setting value into analog and the amplitude of the addition signal. Setting the switch switching time reduces errors in the measurement value.

[0009] (4) The measurement value calculation method of (1) above may further include inputting the sum signal to a first A / D converter to calculate the sum, and inputting the offset signal to a second A / D converter to calculate the offset converted value. By using two A / D converters, the sum and offset converted values ​​are calculated based on output waveforms at the same time. As a result, errors in the measurement value are reduced.

[0010] (5) A measurement value calculation program according to some embodiments causes a measurement value calculation device to perform the following steps: convert an offset setting value into an analog value to generate an offset signal; generate an added signal by adding an input signal and the offset signal; digitally convert the added signal to calculate an added value; digitally convert the offset signal to calculate an offset conversion value; and calculate a measurement value from the added value and the offset conversion value. By calculating the measurement value using the offset conversion value, errors in the measurement value are reduced regardless of delays in the output response of the D / A converter when the offset setting value is changed.

[0011] (6) The measurement value calculation program of (5) may further cause the measurement value calculation device to calculate the addition value and the offset conversion value by using a switch that inputs either the addition signal or the offset signal to an A / D converter. By using a switch to calculate the offset conversion value, the cost of the device can be reduced.

[0012] (7) The measurement value calculation program of (6) may further cause the measurement value calculation device to set the time for switching the switch based on the output characteristics of a D / A converter that converts the offset setting value into analog and the amplitude of the addition signal. Setting the switch switching time reduces errors in the measurement value.

[0013] (8) The measurement value calculation program of (5) above may further cause the measurement value calculation device to input the sum signal to a first A / D converter to calculate the sum value, and input the offset signal to a second A / D converter to calculate the offset conversion value. By using two A / D converters, the sum value and the offset conversion value are calculated based on output waveforms at the same time. As a result, errors in the measurement value are reduced.

[0014] (9) A measurement value calculation device according to some embodiments includes a D / A converter that converts an offset setting value into an analog value and outputs the converted value as an offset signal, an adder circuit that outputs an added signal obtained by adding an input signal and the offset signal, a first A / D converter that digitally converts the added signal to calculate an added value, and an arithmetic circuit that calculates a measurement value from the added value and an offset converted value obtained by digitally converting the offset signal. By calculating the measurement value using the offset converted value, errors in the measurement value are reduced regardless of delays in the output response of the D / A converter when the offset setting value is changed.

[0015] (10) The measurement value calculation device of (9) above may further include a switch that switches to connect either the adder circuit or the D / A converter to the first A / D converter. The first A / D converter may digitally convert the sum signal to calculate the sum when the switch is switched to connect the adder circuit to the first A / D converter, and digitally convert the offset signal to calculate the offset conversion value when the switch is switched to connect the D / A converter to the first A / D converter. By using a switch to calculate the offset conversion value, the cost of the device can be reduced.

[0016] (11) In the measurement value calculation device of (10) above, the switch may switch the connection between the first A / D converter and either the adder circuit or the D / A converter at a switching time that is set based on the output characteristics of the D / A converter and the amplitude of the sum signal. Setting the switch switching time reduces errors in the measurement value.

[0017] (12) The measurement value calculation device of (9) above may further include a second A / D converter that digitally converts the offset signal to calculate the offset conversion value. By using two A / D converters, the sum value and the offset conversion value are calculated based on the output waveform at the same time. As a result, errors in the measurement value are reduced. [Effects of the Invention]

[0018] According to the measurement value calculation method, measurement value calculation program, and measurement value calculation device disclosed herein, the error between the original input signal and the value obtained by subtracting the offset from the signal to which the offset has been applied is reduced. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram showing the configuration of a measurement value calculation device according to a comparative example. [Figure 2] 10 is a graph showing signals and waveforms in a comparative example. [Figure 3] 1 is a block diagram illustrating an example configuration of a measurement value calculation device according to the present disclosure. [Figure 4] 10 is a graph showing an example of a signal and a waveform obtained by a measurement value calculation method according to the present disclosure. [Figure 5] FIG. 1 is a block diagram showing an example of the configuration of a measurement value calculation device that includes a switch for switching input to an A / D converter. [Figure 6] 10 is a graph showing an example of a waveform input from a switch to an A / D converter. [Figure 7] 1 is a flowchart illustrating an example of a procedure for a measurement value calculation method according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Comparative Example) As shown in FIG. 1, a device 90 according to the comparative example includes an arithmetic circuit 91, a D / A converter 92 abbreviated as DAC, an operational amplifier 93 abbreviated as OP, and an A / D converter 94 abbreviated as ADC.

[0021] The D / A converter 92 converts the offset setting value into an analog value and outputs it as an offset signal. The operational amplifier 93 subtracts the offset signal input from the D / A converter 92 to its subtraction terminal (-) from an input signal representing the measurement result of the sensor or the like input from an external sensor or the like to its addition terminal (+), and outputs the resultant signal to the A / D converter 94. The A / D converter 94 outputs a digital value obtained by converting the signal input from the operational amplifier 93 to the arithmetic circuit 91. The arithmetic circuit 91 acquires the offset setting value in the D / A converter 92 and the output value of the A / D converter 94, adds the offset setting value to the output value of the A / D converter 94, and calculates the measurement value of the external sensor or the like.

[0022] The signals and waveforms in the device 90 according to the comparative example are shown in the graph of Fig. 2. The horizontal axis of the graph in Fig. 2 represents time. The voltage of the input signal is assumed to be 2V.

[0023] When the offset setting value of the D / A converter 92 is changed from 0V to 1V, the offset setting value is reflected in the output of the D / A converter 92. Due to a delay in the output response of the D / A converter 92 to changes in the offset setting value, the output of the D / A converter 92 gradually increases from 0V to 1V. Meanwhile, the output of the operational amplifier 93, i.e., the input to the A / D converter 94, gradually decreases from 2V to 1V in response to changes in the output of the D / A converter 92. The output value of the A / D converter 94 is updated with a value obtained by sampling the input waveform to the A / D converter 94 at the timing of the AD conversion signal. The arithmetic circuit 91 adds the offset setting value to the output value of the A / D converter 94 to calculate a measurement value.

[0024] Here, the measurement value calculated by the arithmetic circuit 91 is expected to be equal to the voltage of the input signal. However, due to the effect of a delay in the output response of the D / A converter 92, the measurement value calculated by the arithmetic circuit 91 has an error with respect to 2V, which is the voltage of the input signal, during the period until the transient response of the output of the D / A converter 92 ends. In the comparative example, the period until the transient response of the output of the D / A converter 92 ends is a period during which an error occurs, and is therefore represented as an error occurrence. In other words, in the device 90 according to the comparative example, an error occurs between the value obtained by subtracting the offset from the signal obtained by applying an offset to the input signal and the value of the original input signal. It is necessary to reduce the error.

[0025] Therefore, this disclosure describes a measurement value calculation device 10 (see FIG. 3), a measurement value calculation method, and a measurement value calculation program that can reduce the error between the value obtained by subtracting the offset from the input signal and the original input signal.

[0026] (Configuration example of measurement value calculation device 10) As shown in FIG. 3, a measurement value calculation device 10 according to one embodiment of the present disclosure includes an arithmetic circuit 11, a D / A converter 12 abbreviated as DAC, an operational amplifier 13 abbreviated as OP, a first A / D converter 14 abbreviated as first ADC, and a second A / D converter 15 abbreviated as second ADC.

[0027] The measurement value calculation device 10 is connected to an external sensor or the like, receives a signal representing the detection result of the external sensor or the like as an input signal, applies an offset to the input signal, and calculates a measurement value by digital conversion. The measurement value calculation device 10 may be incorporated into various devices or equipment such as transmitters or field devices.

[0028] The external sensor may be configured to detect various physical quantities and output a signal corresponding to the detected physical quantity. The sensor may include, for example, a pressure sensor that detects a differential pressure or a pressure as the physical quantity. The sensor may include, for example, a temperature sensor that detects a temperature as the physical quantity. The sensor is not limited to these examples and may be configured to detect various other physical quantities. The sensor may output an analog electrical signal, such as a current signal or a voltage signal, as a signal corresponding to the detected physical quantity.

[0029] In the measurement value calculation device 10, the D / A converter 12 converts the offset setting value to an analog value to generate and output an offset signal. The D / A converter 12 branches the offset signal and outputs it to the operational amplifier 13 and the second A / D converter 15. The operational amplifier 13 generates a sum signal by adding an input signal representing the measurement result of the sensor, etc., input to an addition terminal (+) from an external sensor, etc., and an inverted signal of the offset signal input from the D / A converter 12 to a subtraction terminal (-), and outputs the sum signal to the first A / D converter 14. The operational amplifier 13 is also referred to as an adder circuit. The adder circuit may be configured to add the input signal and the offset signal. The first A / D converter 14 digitally converts the sum signal input from the operational amplifier 13 to calculate a sum value and outputs the sum value to the calculation circuit 11. The second A / D converter 15 digitally converts the offset signal input from the D / A converter 12 to calculate an offset conversion value and outputs the offset conversion value to the calculation circuit 11. The arithmetic circuit 11 acquires an addition value from the first A / D converter 14 and an offset conversion value from the second A / D converter 15, and calculates a measurement value from the addition value and the offset conversion value. When the addition circuit adds the input signal and the inverted signal of the offset signal, i.e., when the offset signal is subtracted from the input signal, the arithmetic circuit 11 adds the offset conversion value to the addition value to calculate a measurement value. When the addition circuit adds the input signal and the offset signal, the arithmetic circuit 11 subtracts the offset conversion value from the addition value to calculate a measurement value. The measurement value is a value corresponding to the detection results of various physical quantities input from an external sensor, etc.

[0030] The offset setting value may be set so as to reduce conversion errors when the sum signal is digitally converted by the first A / D converter 14. For example, the offset setting value may be set so that the offset signal is generated as a signal corresponding to the DC component of the input signal.

[0031] The arithmetic circuit 11 may be configured to include a processor such as a CPU (Central Processing Unit) or a dedicated circuit such as an FPGA (Field Programmable Gate Array). The arithmetic circuit 11 may be configured to execute a program including arithmetic processing procedures. The arithmetic circuit 11 may include a memory unit. The memory unit may store various information used in the operation of the arithmetic circuit 11, or a program including arithmetic processing procedures. The memory unit may function as a work memory for the arithmetic circuit 11. The memory unit may be configured, for example, as a semiconductor memory. The memory unit may be configured integrally with the arithmetic circuit 11 or may be configured separately.

[0032] An example of each signal and waveform in the measurement value calculation device 10 according to the present disclosure is shown in the graph of Figure 4. The horizontal axis of the graph in Figure 4 represents time. The voltage of the input signal is assumed to be 2V.

[0033] When the offset setting value of the D / A converter 12 is changed from 0V to 1V, the offset setting value is reflected in the output of the D / A converter 12. Due to a delay in the output response of the D / A converter 12 to a change in the offset setting value, the output of the D / A converter 12 gradually increases from 0V to 1V. Meanwhile, the output of the operational amplifier 13, i.e., the input to the first A / D converter 14, gradually decreases from 2V to 1V in response to the change in the output of the D / A converter 12. Furthermore, the input to the second A / D converter 15, which is the output of the D / A converter 12, gradually increases from 0V to 1V. The output value of the first A / D converter 14 is updated with a value obtained by sampling the input waveform to the first A / D converter 14 at the timing of an AD conversion signal. The output value of the second A / D converter 15 is updated with a value obtained by sampling the input waveform to the second A / D converter 15 at the timing of an AD conversion signal.

[0034] The arithmetic circuit 11 adds the output value of the second A / D converter 15, i.e., the offset conversion value, to the output value of the first A / D converter 14, i.e., the sum value, to calculate a measurement value. Here, the output value of the second A / D converter 15, i.e., the offset conversion value, is a value that reflects the delay in the output response of the D / A converter 12. On the other hand, the offset signal input to the operational amplifier 13 is a value that similarly reflects the delay in the output response of the D / A converter 12. And the output value of the first A / D converter 14, which digitally converts the output of the operational amplifier 13, i.e., the sum value, is a value that similarly reflects the delay in the output response of the D / A converter 12. In other words, the delay in the output response of the D / A converter 12 is reflected in both the sum value and the offset conversion value. By calculating a measurement value by adding the sum value and the offset conversion value, both of which reflect the delay in the output response of the D / A converter 12, the effect of the delay in the output response of the D / A converter 12 on the measurement value is reduced. As a result, the error between the input signal and the measurement value calculated in response to the input signal is reduced.

[0035] In the example of Fig. 4, the error in the measurement value for the input signal is resolved even during the period until the end of the transient response of the output of D / A converter 12. Therefore, since the error is resolved during the period until the end of the transient response of the output of D / A converter 12, this period is represented as "error resolved," unlike Fig. 2.

[0036] As described above, the measurement value calculation device 10 in Fig. 3 reduces errors in the measurement value regardless of the delay in the output response of the D / A converter 12 when the offset setting value is changed. Furthermore, by using two A / D converters, namely the first A / D converter 14 and the second A / D converter 15, the addition value and the offset conversion value are calculated based on the output waveform at the same time. As a result, errors in the measurement value are reduced.

[0037] (Configuration example of measurement value calculation device 10A equipped with switch 16) As shown in Fig. 5, the measurement value calculation device 10A includes an arithmetic circuit 11, a D / A converter 12 abbreviated as DAC, an operational amplifier 13 abbreviated as OP, a first A / D converter 14 abbreviated as first ADC, and a switch 16. The measurement value calculation device 10A differs from the measurement value calculation device 10 of Fig. 3 in that it does not include a second A / D converter 15 abbreviated as second ADC, but includes a switch 16. The switch 16 has a contact that can be switched so that either the output of the operational amplifier 13 or the output of the D / A converter 12 is connected to the first A / D converter 14. The switch 16 may be configured to switch the connection using a mechanical contact, or may be configured to switch the connection using an electrical contact.

[0038] In the measured value calculation device 10A, the D / A converter 12 converts the offset setting value into an analog signal and outputs it as an offset signal. The D / A converter 12 branches the offset signal and outputs it to the operational amplifier 13 and the switch 16. The operational amplifier 13 adds an input signal input to an addition terminal (+) from an external sensor or the like to an inverted signal of the offset signal input to a subtraction terminal (-) from the D / A converter 12, and outputs an added signal to the switch 16. The operational amplifier 13 is also referred to as an adder circuit. The adder circuit may be configured to add the input signal and the offset signal. When the first A / D converter 14 is connected to the output of the operational amplifier 13 by the switch 16, it digitally converts the added signal input from the operational amplifier 13 and outputs the resulting added value to the calculation circuit 11. When the first A / D converter 14 is connected to the output of the D / A converter 12 by the switch 16, it digitally converts the offset signal input from the D / A converter 12 and outputs the resulting offset-converted value to the calculation circuit 11. The arithmetic circuit 11 acquires the sum and offset converted values ​​from the first A / D converter 14 and calculates a measurement value from the sum and offset converted values. When the adder circuit adds the input signal and the inverted signal of the offset signal, i.e., when the adder circuit subtracts the offset signal from the input signal, the arithmetic circuit 11 adds the offset converted value to the sum to calculate a measurement value. When the adder circuit adds the input signal and the offset signal, the arithmetic circuit 11 subtracts the offset converted value from the sum to calculate a measurement value. The measurement values ​​are values ​​corresponding to the detection results of various physical quantities input from external sensors, etc.

[0039] Here, the first A / D converter 14 cannot simultaneously digitally convert the output of the operational amplifier 13 and the output of the D / A converter 12. In other words, the output signal of the operational amplifier 13 corresponding to the sum value and the offset signal of the D / A converter 12 corresponding to the offset conversion value are signals output at different times.

[0040] As shown in FIG. 6, the output of the first A / D converter 14 is determined depending on the connection of the switch 16. The horizontal axis of the graph in FIG. 6 represents time. When the switch 16 switches the contact to connect the D / A converter 12 to the first A / D converter 14, the output waveform of the D / A converter 12 is input to the first A / D converter 14. As a result, the first A / D converter 14 outputs an offset conversion value obtained by digitally converting the output waveform of the D / A converter 12. On the other hand, when the switch 16 switches the contact to connect the operational amplifier 13 to the first A / D converter 14, the output waveform of the operational amplifier 13 is input to the first A / D converter 14. As a result, the first A / D converter 14 outputs an added value obtained by digitally converting the output waveform of the operational amplifier 13.

[0041] 6, the time it takes for the switch 16 to switch the connection is represented as the switching time. The switching time is represented as the time from the center of a period in which the switch 16 is connected to the D / A converter 12 to the center of a period in which the switch 16 is connected to the operational amplifier 13. The switching time may be represented as the time from when the connection of the switch 16 is switched to the D / A converter 12 to when the connection of the switch 16 is next switched to the operational amplifier 13. The switching time may be represented as the time from the center of a period in which the connection of the switch 16 is the operational amplifier 13 to the center of a period in which the connection of the switch 16 is the D / A converter 12. The switching time may be represented as the time from when the connection of the switch 16 is switched to the operational amplifier 13 to when the connection of the switch 16 is next switched to the D / A converter 12.

[0042] While the switching time elapses, both the output of D / A converter 12 and the output of operational amplifier 13 change. For example, while the switching time elapses, the output of D / A converter 12 changes by a value represented as the amount of output change. Here, the output of D / A converter 12 during the period when switch 16 is connected to D / A converter 12 and the output of D / A converter 12 during the period when switch 16 is connected to operational amplifier 13 are represented by the outputs at the center of the respective periods.

[0043] From the above, when switch 16 switches the connection destination of first A / D converter 14 between operational amplifier 13 and D / A converter 12, when arithmetic circuit 11 acquires the sum, the offset conversion value corresponding to that sum is a digital conversion value of the offset signal before and after the change by the output change amount. As a result, the measurement value calculated by arithmetic circuit 11 has an error corresponding to the output change amount.

[0044] Here, the shorter the switching time of the switch 16, the smaller the amount of change in the output of the D / A converter 12. The measurement value calculation device 10A may shorten the switching time of the switch 16 so that the amount of change in the output of the D / A converter 12 falls within the allowable error range of the measurement value. The allowable error range of the measurement value may be set based on the amplitude of the sum signal. For example, the allowable error range for an add signal with an amplitude of 20 mV may be set to ±0.05 mV. The switching time of the switch 16 may be set so that the amount of change in the output of the D / A converter 12 falls within the range of ±0.05 mV.

[0045] The amount of change in the output of the D / A converter 12 is determined based on the output characteristics, such as the delay in the output response of the D / A converter 12. Therefore, the measurement value calculation device 10A may set the switching time of the switch 16 based on the output characteristics of the D / A converter 12 and the amplitude of the addition signal. Setting the switching time in this manner reduces errors in the measurement value.

[0046] As described above, according to the measurement value calculation device 10A of Fig. 5, by adding the switch 16 without adding the second A / D converter 15, errors in the measurement value are reduced regardless of the delay in the output response of the D / A converter 12 when the offset setting value is changed. Errors in the measurement value are reduced. Furthermore, by calculating the offset conversion value using the switch 16, the cost of the measurement value calculation device 10A can be reduced.

[0047] (Example of procedure for calculating measurement values) The measurement value calculation device 10 or 10A may execute a measurement value calculation method including the example steps of the flowchart illustrated in Fig. 7. The measurement value calculation method may be realized as a measurement value calculation program executed by a processor constituting the measurement value calculation device 10 or 10A. The measurement value calculation program may be stored in a non-transitory computer-readable medium.

[0048] The measurement value calculation device 10 or 10A generates an offset signal using the D / A converter 12 (step S1). The measurement value calculation device 10 or 10A adds the input signal and the offset signal using the operational amplifier 13 to generate an added signal (step S2).

[0049] The measurement value calculation device 10 or 10A digitally converts the sum signal and the offset signal (step S3). Specifically, the measurement value calculation device 10 digitally converts the sum signal using the first A / D converter 14 to calculate the sum, and digitally converts the offset signal using the second A / D converter 15 to calculate the offset conversion value. The measurement value calculation device 10A switches the connection of the switch 16 to the operational amplifier 13 to calculate the sum using the first A / D converter 14, and switches the connection of the switch 16 to the D / A converter 12 to calculate the offset conversion value using the first A / D converter 14.

[0050] The measurement value calculation device 10 or 10A calculates a measurement value from the added value and the offset converted value using the arithmetic circuit 11 (step S4). After executing the procedure of step S4, the measurement value calculation device 10 or 10A ends the procedure of the flowchart in Fig. 7. The measurement value calculation device 10 or 10A may repeatedly execute the procedures from steps S1 to S4.

[0051] (summary) As described above, according to the measurement value calculation device 10 or 10A, measurement value calculation method, or measurement value calculation program of this embodiment, a measurement value is calculated using an offset conversion value obtained by digitally converting the offset signal output from the D / A converter 12. As a result, errors in the measurement value are reduced regardless of delays in the output response of the D / A converter 12 when the offset setting value is changed.

[0052] The above describes an embodiment of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and various modifications are also included within the scope that does not deviate from the spirit of the present disclosure. [Explanation of symbols]

[0053] 10, 10A measurement value calculation device (11: arithmetic circuit, 12: D / A converter, 13: operational amplifier, 14: first A / D converter, 15: second A / D converter, 16: switch)

Claims

1. converting the offset setting value into an analog signal to generate an offset signal; generating a sum signal by adding an input signal and the offset signal; converting the sum signal into a digital signal to calculate a sum; converting the offset signal into a digital value to calculate an offset conversion value; calculating a measurement value from the added value and the offset converted value; A measurement value calculation method including:

2. 2. The measurement value calculation method according to claim 1, further comprising: switching a switch that inputs one of the addition signal and the offset signal to an A / D converter, and calculating the addition value and the offset conversion value using the A / D converter.

3. 3. The measurement value calculation method according to claim 2, further comprising setting the time for switching the switch based on the output characteristics of a D / A converter that converts the offset setting value into an analog value and the amplitude of the addition signal.

4. inputting the sum signal to a first A / D converter to calculate the sum value; inputting the offset signal to a second A / D converter to calculate the offset conversion value; The method of claim 1 further comprising:

5. converting the offset setting value into an analog signal to generate an offset signal; generating a sum signal by adding an input signal and the offset signal; converting the sum signal into a digital signal to calculate a sum; converting the offset signal into a digital value to calculate an offset conversion value; calculating a measurement value from the added value and the offset converted value; A measurement value calculation program that causes a measurement value calculation device to execute the above.

6. 6. The measurement value calculation program according to claim 5, further causing the measurement value calculation device to change a switch that inputs one of the addition signal and the offset signal to an A / D converter, and calculate the addition value and the offset converted value using the A / D converter.

7. 7. The measurement value calculation program according to claim 6, further causing the measurement value calculation device to set the time for switching the switch based on the output characteristics of a D / A converter that converts the offset setting value into analog and the amplitude of the addition signal.

8. inputting the sum signal to a first A / D converter to calculate the sum value; inputting the offset signal to a second A / D converter to calculate the offset conversion value; The measurement value calculation program according to claim 5 , further causing the measurement value calculation device to execute the following:

9. a D / A converter that converts the offset setting value into an analog value and outputs the analog value as an offset signal; an adder circuit that outputs a sum signal obtained by adding an input signal and the offset signal; a first A / D converter that digitally converts the sum signal to calculate a sum; an arithmetic circuit that calculates a measurement value from the added value and an offset conversion value obtained by digitally converting the offset signal; A measurement value calculation device comprising:

10. a switch for switching to connect one of the adder circuit or the D / A converter to the first A / D converter; The first A / D converter When the switch is switched so as to connect the adder circuit to the first A / D converter, the adder signal is digitally converted to calculate the adder value; When the switch is switched so as to connect the D / A converter to the first A / D converter, the offset signal is digitally converted to calculate the offset conversion value. The measurement value calculation device according to claim 9 .

11. 11. The measurement value calculation device according to claim 10, wherein the switch switches the connection between the first A / D converter and one of the adder circuit or the D / A converter at a switching time that is set based on the output characteristics of the D / A converter and the amplitude of the summation signal.

12. The measurement value calculation device according to claim 9 , further comprising a second A / D converter that digitally converts the offset signal to calculate the offset conversion value.

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