JP6270690B2 - Electromagnetic flow meter converter and electromagnetic flow meter calibration method - Google Patents

Description

  The present invention relates to a technique for calibrating a transducer of an electromagnetic flow meter.

  As a cause of the variation in performance of the electromagnetic flow meter, there is a variation in the electronic circuit used in the converter of the electromagnetic flow meter, specifically, a variation in the characteristics of the operational amplifier and the AD converter. Conventionally, as shown in FIG. 6, a calibrator 3 is connected to the converter 2 instead of the detector 1 of the electromagnetic flow meter, and a reference flow rate signal (e.g., electromotive force) equivalent to the flow rate signal (electromotive force) from the detector 1 is used. The converter 2 is calibrated by inputting a voltage corresponding to a flow velocity of 10 m / s, 2.5 m / s, and 0 m / s from the calibrator 3 to the converter 2 (see Patent Document 1).

JP 7-146165 A

  As described above, calibration work for conventional electromagnetic flowmeters requires the preparation of a calibrator that generates an accurate signal voltage for each model, and the calibration of the calibrator itself. It took time and effort.

  The present invention has been made to solve the above-described problems, and can reduce the labor required for calibration work, and without the need for special equipment such as a calibrator, The purpose is to be able to calibrate.

The converter of the electromagnetic flow meter of the present invention includes an amplifier circuit that amplifies the flow signal input from the detector of the electromagnetic flow meter, an AD converter that converts the flow signal amplified by the amplifier circuit into a digital signal, A flow rate calculating means for converting an output value of the AD converter into a flow rate value, a pseudo flow signal generating means for generating a pseudo flow signal in the calibration mode, and a signal output terminal for outputting the pseudo flow signal to an external voltmeter; A selection means for inputting a flow rate signal from the detector to the amplifier circuit in the normal mode, and a pseudo flow rate signal from the pseudo flow signal generation means to the amplification circuit in the calibration mode; Using the voltage value of the pseudo flow signal measured by the voltmeter and the output value of the AD converter obtained by inputting the pseudo flow signal, the flow velocity calculation is performed. Zeroing means and is characterized in that it comprises a calibration means for adjusting the gain.
Further, in one configuration example of the converter of the electromagnetic flowmeter of the present invention, the pseudo flow signal generating means includes a pseudo flow signal output means for outputting a digital value of the pseudo flow signal, and a digital value of the pseudo flow signal. It is characterized by comprising a DA converter for converting to an analog signal and a step-down circuit for stepping down the output signal of the DA converter.

Further, in one configuration example of the converter of the electromagnetic flowmeter of the present invention, the pseudo flow signal generating means sequentially generates a plurality of pseudo flow signals having different corresponding flow velocity values in the calibration mode, and the calibration means Using the voltage value of the plurality of pseudo flow signals and the output value of the AD converter for each pseudo flow signal, an equation indicating the relationship between the output value of the AD converter and the flow velocity value is obtained, and zero adjustment of the flow velocity calculation means The gain adjustment is performed.
In the configuration example of the converter of the electromagnetic flowmeter of the present invention, the pseudo flow signal output means linearly changes the digital value of the pseudo flow signal in the linearity confirmation mode. It is.
Moreover, one configuration example of the converter of the electromagnetic flowmeter of the present invention further stores a digital value of the pseudo flow signal output in the calibration mode and an output value of the AD converter, and in the diagnosis mode, The digital value of the stored pseudo flow signal is output from the pseudo flow signal output means, and the characteristics of the amplifier circuit, the AD converter, and the DA converter are changed based on the output value of the AD converter obtained at this time. It is characterized by comprising diagnostic means for diagnosing whether or not there is.

  The present invention also provides an amplifier circuit that amplifies a flow signal input from a detector of an electromagnetic flow meter, an AD converter that converts the flow signal amplified by the amplifier circuit into a digital signal, and an output value of the AD converter In a calibration method for calibrating a transducer of an electromagnetic flowmeter having a flow velocity calculation means for converting a flow velocity value into a flow velocity value, a pseudo flow signal is generated in a calibration mode, and the pseudo flow rate is substituted for the flow signal from the detector. A pseudo flow signal generation step of inputting a signal to the amplifier circuit, a measurement step of measuring a voltage value of the pseudo flow signal with an external voltmeter, and a voltage of the pseudo flow signal measured by the voltmeter in the calibration mode Calibration that performs zero adjustment and gain adjustment of the flow velocity calculation means using the value and the output value of the AD converter obtained by inputting the pseudo flow signal It is characterized in that comprises a step.

  According to the present invention, since the electromagnetic flowmeter can be calibrated only by the converter without using a calibrator, it is not necessary to develop a calibrator, and the labor and preparation required for calibration work can be reduced. Can do. Since the voltmeter is a measuring instrument that has been used for calibration work of electromagnetic flowmeters, it is not necessary to prepare a voltmeter for the calibration work.

  In the present invention, the linearity of the converter can be confirmed by linearly changing the digital value of the pseudo flow rate signal in the linearity confirmation mode.

  In the present invention, it is possible to diagnose whether or not there is a change in the characteristics of the electronic circuit (amplifier circuit, AD converter, and DA converter) of the converter by providing diagnostic means.

It is a figure explaining the outline | summary of the calibration method of the electromagnetic flowmeter which concerns on embodiment of this invention. It is a block diagram explaining the calibration method of the electromagnetic flowmeter which concerns on embodiment of this invention. It is a figure which shows the signal waveform of each part of an electromagnetic flowmeter. It is a functional block diagram of CPU of the converter of the electromagnetic flowmeter which concerns on embodiment of this invention. It is a flowchart explaining the calibration method of the electromagnetic flowmeter which concerns on embodiment of this invention. It is a figure explaining the conventional calibration method of an electromagnetic flowmeter.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an outline of a calibration method for an electromagnetic flowmeter according to an embodiment of the present invention. In this embodiment, a pseudo flow signal corresponding to the flow signal (electromotive force) from the detector 1 is generated inside the converter 2a, the voltage of the generated flow signal is measured by the voltmeter 4, and the reading is converted. The converter 2a is calibrated by inputting to the converter 2a. The voltmeter 4 includes a digital voltmeter or a digital multimeter.

  FIG. 2 is a block diagram for explaining a method for calibrating the electromagnetic flowmeter according to the present embodiment. The detector 1 of the electromagnetic flow meter is disposed in an excitation coil 10 that generates a magnetic field and a magnetic field generated from the excitation coil 10, and detects an electromotive force generated when a fluid to be measured flows in the magnetic field. And a measuring tube 11 that outputs a flow rate signal proportional to the flow velocity.

  At the time of normal measurement, the converter 2a supplies an excitation current as shown in FIG. 3A to the excitation coil 10 of the detector 1, and a flow rate signal as shown in FIG. Is converted to a flow rate value. The converter 2a of this embodiment includes an excitation circuit 20 that outputs an excitation current, an amplification circuit 21 that amplifies the input flow rate signal, and a CPU (Central Processing Unit) that converts the amplified flow rate signal into a flow velocity value. 22, setting of the converter 2 a and setting / display unit 23 for displaying information to the user of the electromagnetic flowmeter, an inversion converter 24 for inverting the pseudo flow rate signal output from the CPU 22, and a pseudo output output from the CPU 22 From the step-down circuit 25-1 for stepping down the flow rate signal, the step-down circuit 25-2 for stepping down the pseudo flow rate signal output from the inverting converter 24, the flow rate signal from the detector 1 and the step-down circuits 25-1, 25-2. And selection circuits 26-1 and 26-2 for selecting one of the pseudo flow rate signals.

  The excitation circuit 20, the amplifier circuit 21, and the setting / display device 23 have the same configuration as that of the conventional converter. However, in this embodiment, the inverting converter 24 and the step-down circuits 25-1 and 25 are added to the conventional converter. -2, selection circuits 26-1 and 26-2, a signal output terminal D, and a ground terminal F are added, and the program of the CPU 22 is changed. As shown in FIG. 4, the CPU 22 includes a DA (Digital-to-Analog) converter 220, an AD (Analog-to-Digital) converter 222, a storage unit 227, a pseudo flow rate signal output unit 223, The flow rate calculation means 224, the calibration means 225, the control means 226, and the diagnosis means 228 are comprised. The pseudo flow signal output means 223, the DA converter 220, the inverting converter 24, and the step-down circuits 25-1 and 25-2 constitute pseudo flow signal generation means.

  Hereinafter, the operation of the present embodiment will be described. The CPU 22 of the converter 2a includes a pseudo flow rate signal output unit 223, a flow rate calculation unit according to a program stored in a storage unit 227 arranged inside the CPU 22 or a program stored in a storage device (not shown) arranged outside. 224, calibration means 225, control means 226, and diagnosis means 228, and performs the following processing.

  In the normal measurement mode, the control means 226 of the converter 2a controls the selection circuits 26-1 and 26-2 to select the output of the detector 1. Thereby, the flow signal from the detector 1 is input to the amplifier circuit 21. Since the flow rate signal input from the detector 1 to the converter 2a is a minute signal on the order of μV, it is amplified by the amplifier circuit 21 to a sufficient voltage level. The amplified flow rate signal is converted into a digital signal by the AD converter 222 in the CPU 22. The flow velocity calculation means 224 converts the output value of the AD converter 222 into a flow velocity value.

  Next, the calibration method of the present embodiment will be described using the flowchart of FIG. First, the calibration operator connects the signal output terminal D of the converter 2a and the plus terminal of the voltmeter 4, and connects the minus terminal of the voltmeter 4 and the ground terminal F of the converter 2a. For example, when the calibration operator sets the calibration mode using the setting / display device 23, the control means 226 of the converter 2a controls the selection circuits 26-1 and 26-2 to control the step-down circuits 25-1 and 25-2. Are selected (step S100 in FIG. 5). As a result, the outputs of the step-down circuits 25-1 and 25-2 are input to the amplifier circuit 21.

  Next, the pseudo flow signal output means 223 of the converter 2a outputs a digital value of the pseudo flow signal. The digital value of the pseudo flow rate signal is converted into an analog voltage by the DA converter 220 in the CPU 22, and further divided by 1/600, for example, by a step-down circuit 25-1 made of a precision resistor, and stepped down to a signal of μV order. On the other hand, the inverting converter 24 generates a signal having the same absolute value as the pseudo flow rate signal output from the DA converter 220 and having the polarity inverted. That is, if the pseudo flow signal output from the DA converter 220 is a positive voltage signal, a negative voltage signal is generated. If the pseudo flow signal output from the DA converter 220 is a negative voltage signal, the positive voltage is generated. Generate a signal. The signal output from the inverting converter 24 is divided by 1/600 by a step-down circuit 25-2 having the same configuration as that of the step-down circuit 25-1, and is stepped down to a μV order signal. The outputs of the step-down circuits 25-1 and 25-2 are input to the amplifier circuit 21 via the selection circuits 26-1 and 26-2. The pseudo flow signal amplified by the amplifier circuit 21 is converted into a digital signal by the AD converter 222 (step S101 in FIG. 5).

  The flow rate signal input from the detector 1 is a differential signal, and the amplifier circuit 21 is also an amplifier circuit corresponding to the differential signal. Further, as apparent from FIGS. 3A and 3B, the detector 1 outputs a positive flow rate signal when the excitation current is positive, and the negative electrode when the excitation current is negative. The flow rate signal is output.

  Therefore, in order to correspond to the configuration of the amplifier circuit 21, the polarity of the pseudo flow signal output from the pseudo flow signal output means 223 is also switched, and the inverting converter 24, the step-down circuits 25-1, 25-2, and the selection circuit are switched. 26-1 and 26-2 correspond to a differential signal. The pseudo flow signal output means 223 generates a positive pseudo flow signal at a timing when the excitation current is positive, and generates a negative pseudo flow signal at a timing when the excitation current is negative. Since the CPU 22 performs switching between the positive polarity and the negative polarity of the excitation current, the polarity of the pseudo flow rate signal is also switched by inverting the sign of the DA count value at this timing.

The storage means 227 of the CPU 22 stores the output value of the AD converter 222 (step S102 in FIG. 5).
Next, the polarity switching of the pseudo flow signal is stopped, and the voltmeter 4 measures the output voltage (voltage of the signal output terminal D) of the DA converter 220 before stepping down the pseudo flow signal (step S103 in FIG. 5). The pseudo flow signal output from the step-down circuits 25-1 and 25-2 is one hundredth (for example, 1/600) times the measured voltage. The calibration operator inputs the measured voltage value to the CPU 22, and the storage means 227 of the CPU 22 stores the input voltage value (step S104 in FIG. 5). It is necessary to multiply this voltage value by the voltage dividing ratio of the step-down circuits 25-1 and 25-2 to obtain the voltage of the pseudo flow rate signal. This processing is performed by the calibration means 225 of the CPU 22. Normally, the calibration operator manually inputs the reading value of the voltmeter 4 by operating the setting / display unit 23. However, if the voltmeter 4 and the converter 2a are provided with communication means, the voltmeter is communicated. Four readings may be taken.

  The CPU 22 performs the generation and capture of the pseudo flow signal as described above a plurality of times while changing the flow velocity value. For example, three types of pseudo flow signals corresponding to flow rates of 10 m / s, 2.5 m / s, and 0 m / s are generated, and the processes of steps S101 to S04 are performed for each pseudo flow signal.

  When the calibration unit 225 of the converter 2a completes the generation and capture of all the pseudo flow signals (YES in step S105 in FIG. 5), the voltage value of the pseudo flow signal measured by the voltmeter 4 and the AD converter 222 From the output value D, an expression showing the relationship between the output value D of the AD converter 222 and the fluid flow velocity value S is obtained (step S106 in FIG. 5).

Now, the voltage value obtained by measuring the pseudo flow signal corresponding to the flow velocity of 0 m / s with the voltmeter 4 is V0, and the output value of the AD converter 222 when the pseudo flow signal corresponding to the flow velocity of 0 m / s is input to the amplifier circuit 21. Is a voltage value obtained by measuring a pseudo flow signal corresponding to D0, a flow velocity of 2.5 m / s with the voltmeter 4 by V2.5, and a pseudo flow signal corresponding to the flow velocity of 2.5 m / s is input to the amplifier circuit 21. The output value of the AD converter 222 is D2.5, the pseudo flow signal corresponding to the flow rate of 10 m / s is measured by the voltmeter 4, the voltage value is V10, and the pseudo flow signal corresponding to the flow rate of 10 m / s is supplied to the amplifier circuit 21. When the output value of the AD converter 222 at the time of input is D10, the flow rate value S0 calculated when a pseudo flow rate signal corresponding to a flow rate of 0 m / s is input to the amplifier circuit 21 and the flow rate of 2.5 m / s are equivalent. Doubt The flow rate value S2.5 calculated when the flow rate signal is input to the amplification circuit 21 and the flow rate value S10 calculated when the pseudo flow rate signal corresponding to the flow rate of 10 m / s is input to the amplification circuit 21 are as follows. Become.
S0 = V0 × r / E (1)
S2.5 = V2.5 × r / E (2)
S10 = V10 × r / E (3)

r is a voltage division ratio (for example, 1/600) of the step-down circuits 25-1 and 25-2, and E is an electromotive force (inductive voltage) per 1 m / s determined for each detector. The calibration means 225 obtains the following straight line expression that passes through the three points (D0, S0), (D2.5, S2.5), and (D10, S10) by the least square method. A is a gain and B is an offset.
S = A × D + B (4)

  Then, the calibration unit 225 stores the adjustment value (A, B) calculated in step S106 in the storage unit 227 (step S107 in FIG. 5). This completes the zero adjustment and gain adjustment of the flow velocity calculation means 224, and the calibration of the electromagnetic flow meter is completed. Thereafter, the flow velocity calculation means 224 can easily calculate the flow velocity value S from the output value D of the AD converter 222 by using the gain A and the offset B updated in step S107 according to the equation (4).

  In consideration of linearity, a straight line determined by (D0, S0) and (D2.5, S2.5) and a straight line determined by (D2.5, S2.5) and (D10, S10) may be approximated by a broken line. Good.

  In the present embodiment, the electromagnetic flow meter can be calibrated without using a calibrator, so that the cost required for the calibration work can be reduced. In the present embodiment, since the voltage value of the pseudo flow signal is measured by the voltmeter 4, the pseudo flow signal generated inside the converter may not be an accurate value corresponding to a desired flow velocity value. A voltmeter 4 such as a digital voltmeter or a digital multimeter is used for measurement of excitation current and 4-20 mA current output, and is a measuring instrument that has been used for calibration work. Therefore, it is not necessary to prepare the voltmeter 4 again for the calibration work.

  In the present embodiment, a test for linearity confirmation can be performed by changing the output of the DA converter 220 after the calibration is completed. For example, when the calibration operator sets the linearity confirmation mode using the setting / display device 23, the pseudo flow signal output means 223 linearly changes the digital value of the pseudo flow signal. Thereby, if the flow velocity value continuously calculated by the flow velocity calculating means 224 is confirmed, the linearity of the converter 2a can be confirmed.

  Further, since the digital value of the pseudo flow rate signal output in the calibration mode and the output value of the AD converter 222 are stored in association with each other in the storage unit 227, an electronic circuit (amplifier circuit 21, AD converter 222, DA converter 220) is stored. ) Whether or not there is a change in the characteristics.

  Specifically, for example, when the calibration operator sets the diagnosis mode using the setting / display device 23, the diagnosis unit 228 uses the pseudo flow rate signal output unit 223 as the digital value of the pseudo flow rate signal stored in the storage unit 227. Output from. At this time, the control means 226 controls the selection circuits 26-1 and 26-2 to select the outputs of the step-down circuits 25-1 and 25-2. As a result, since the output value of the AD converter 222 is obtained in the same manner as described above, the diagnosis unit 228 stores the value in the storage unit 227 as a value corresponding to the digital value of the pseudo flow rate signal newly generated by the pseudo flow rate signal output unit 223. The stored output value of the AD converter 222 is compared with the newly acquired output value of the AD converter 222, and the newly acquired output value of the AD converter 222 is stored in the storage unit 227. The AD converter determines that the characteristic of the electronic circuit has changed when it is out of a predetermined error range centered on the output value of the AD converter, and the newly acquired output value of the AD converter 222 is stored in the storage means 227 If it is within a predetermined error range centered on the output value 222, it is determined that there is no change in the characteristics of the electronic circuit.

  Further, in the present embodiment, a pseudo flow rate signal having an arbitrary waveform can be generated by the converter alone, so that the operation test of the electronic circuit and the software operation test can be easily performed by the converter alone.

  The present invention can be applied to a technique for calibrating a transducer of an electromagnetic flow meter.

  DESCRIPTION OF SYMBOLS 1 ... Detector, 2a ... Converter, 4 ... Voltmeter, 10 ... Excitation coil, 11 ... Measuring tube, 20 ... Excitation circuit, 21 ... Amplification circuit, 22 ... CPU, 23 ... Setting and display, 24 ... Inverting converter , 25-1, 25-2 ... step-down circuit, 26-1, 26-2 ... selection circuit, 220 ... DA converter, 222 ... AD converter, 223 ... pseudo flow signal output means, 224 ... flow velocity calculation means, 225 ... calibration Means, 226... Control means, 227... Storage means, 228.

Claims (10)

An amplifying circuit for amplifying the flow signal input from the detector of the electromagnetic flow meter;
An AD converter that converts the flow rate signal amplified by the amplifier circuit into a digital signal;
A flow velocity calculating means for converting the output value of the AD converter into a flow velocity value;
Pseudo flow signal generation means for generating a pseudo flow signal in the calibration mode;
A signal output terminal for outputting the pseudo flow signal to an external voltmeter;
A selection unit that inputs a flow rate signal from the detector to the amplification circuit in a normal mode, and a pseudo flow rate signal from the pseudo flow rate signal generation unit to the amplification circuit in the calibration mode;
Using the voltage value of the pseudo flow signal measured by the voltmeter in the calibration mode and the output value of the AD converter obtained by inputting the pseudo flow signal, zero adjustment and gain adjustment of the flow velocity calculation means are performed. An electromagnetic flowmeter converter comprising: calibration means for performing. The transducer of the electromagnetic flowmeter according to claim 1,
The pseudo flow signal generating means is
Pseudo flow signal output means for outputting a digital value of the pseudo flow signal;
A DA converter that converts the digital value of the pseudo flow rate signal into an analog signal;
An electromagnetic flowmeter converter comprising a step-down circuit for stepping down the output signal of the DA converter. In the converter of the electromagnetic flowmeter according to claim 1 or 2,
The pseudo flow signal generation means sequentially generates a plurality of pseudo flow signals having different flow velocity values corresponding to the calibration mode,
The calibration means uses the voltage values of the plurality of pseudo flow signals and the output values of the AD converter for each pseudo flow signal to obtain an expression indicating the relationship between the output value of the AD converter and the flow velocity value, and calculates the flow velocity. An electromagnetic flowmeter converter characterized by performing zero adjustment and gain adjustment of the means. The transducer of the electromagnetic flowmeter according to claim 2,
The pseudo flow signal output means linearly changes the digital value of the pseudo flow signal in the linearity confirmation mode. The transducer of the electromagnetic flowmeter according to claim 2,
Further, the digital value of the pseudo flow signal output in the calibration mode and the output value of the AD converter are stored, and the stored digital value of the pseudo flow signal is stored in the pseudo flow signal output means in the diagnosis mode. And a diagnostic means for diagnosing whether there is a change in characteristics of the amplifier circuit, the AD converter, and the DA converter based on the output value of the AD converter obtained at this time. Electromagnetic flow meter converter. An amplification circuit that amplifies the flow signal input from the detector of the electromagnetic flow meter, an AD converter that converts the flow signal amplified by the amplification circuit into a digital signal, and an output value of the AD converter is converted into a flow velocity value. In a calibration method for calibrating a transducer of an electromagnetic flow meter provided with a flow velocity calculation means,
A pseudo flow signal generating step of generating a pseudo flow signal in the calibration mode and inputting the pseudo flow signal to the amplifier circuit instead of the flow signal from the detector;
A measurement step of measuring the voltage value of the pseudo flow signal with an external voltmeter;
Using the voltage value of the pseudo flow signal measured by the voltmeter in the calibration mode and the output value of the AD converter obtained by inputting the pseudo flow signal, zero adjustment and gain adjustment of the flow velocity calculation means are performed. A calibration method for an electromagnetic flowmeter, comprising: a calibration step to be performed. The electromagnetic flowmeter calibration method according to claim 6,
The pseudo flow signal generation step includes
A pseudo flow signal output step for outputting a digital value of the pseudo flow signal;
A DA conversion step for converting the digital value of the pseudo flow signal into an analog signal by a DA converter;
And a step of stepping down the output signal of the DA converter by a step-down circuit. The electromagnetic flowmeter calibration method according to claim 6 or 7,
In the calibration flow mode, the pseudo flow signal generation step sequentially generates a plurality of pseudo flow signals having different corresponding flow velocity values,
The calibration step uses the voltage value of the plurality of pseudo flow signals and the output value of the AD converter for each pseudo flow signal to obtain an expression indicating the relationship between the output value of the AD converter and the flow velocity value, and calculates the flow velocity. A method for calibrating an electromagnetic flowmeter, characterized by performing zero adjustment and gain adjustment of the means. The electromagnetic flowmeter calibration method according to claim 7,
Further, the linearity confirmation mode further includes a linearity confirmation step of linearly changing the digital value of the pseudo flow rate signal. The electromagnetic flowmeter calibration method according to claim 7,
A storage step for storing the digital value of the pseudo flow rate signal output in the calibration mode and the output value of the AD converter;
In the diagnostic mode, the stored digital value of the pseudo flow signal is output, and the characteristics of the amplifier circuit, the AD converter, and the DA converter are changed based on the output value of the AD converter obtained at this time. And a diagnostic step for diagnosing whether or not there is an electromagnetic flowmeter calibration method.