JP4190060B2 - measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a measurement apparatus suitable for measuring voltage and current, and more specifically, a measurement apparatus that integrates an integrated signal based on an input AC signal and measures the voltage and current based on an effective voltage obtained by the integration. It is about.
[0002]
[Prior art]
As a measurement system for confirming the torque characteristics of a motor, a measurement system S2 shown in FIG. 4 is conventionally known. In the measurement system S2, first, the inverter device 2 converts the voltage and frequency of the input commercial alternating current (U, V, W) to supply, for example, an alternating voltage VAC of 2 Hz to 120 Hz to the motor M. . At this time, the effective voltage of the AC voltage VAC supplied to the motor M is measured by the voltmeter 51, and the torque of the motor is measured by a torque meter (not shown). As a result, the relationship of the torque of the motor M with respect to the voltage supplied to the motor M can be obtained based on both measured values. As a result, what is the maximum AC voltage applied to the motor M? It can be confirmed whether the motor M rotates efficiently.
[0003]
The voltmeter 51 in the conventional measurement system S2 has an effective voltage measuring unit 11 that measures the effective voltage of the AC voltage VAC and an effective voltage Vrms measured by the effective voltage measuring unit 11, as shown in FIG. A calculation unit 12 that generates measurement data DM for the effective voltage by performing calculation processing based on the calculation process, and a display unit 13 that displays the effective voltage based on the measurement data DM output from the calculation unit 12 are provided.
[0004]
The effective voltage measurement unit 11 includes an absolute value circuit 31, a square / divide circuit 32, and an integration circuit 33. As an external circuit for switching the integration time constant of the integration circuit 33, an inverter circuit 14 and an analog switch 15 are provided. 16, a large-capacity averaging capacitor 17, a small-capacitance averaging capacitor 18, a changeover switch 52 for switching between the averaging capacitors 17 and 18, and a pull-up resistor 53.
[0005]
In the voltmeter 51, when the AC voltage VAC is input, the absolute value circuit 31 calculates a voltage Va corresponding to the absolute value of the AC voltage VAC by analog calculation. Next, the square / divide circuit 32 squares the voltage Va, and generates a voltage Vb by dividing the voltage squared by the voltage Va by the effective voltage Vrms output from the integrating circuit 33. Output to the integration circuit 33. Thereafter, the integration circuit 33 integrates the voltage Vb to generate an effective voltage Vrms, and outputs the effective voltage Vrms to the calculation unit 12.
[0006]
In this case, the integrating circuit 33 substantially functions as a smoothing circuit. For this reason, if a ripple voltage is superimposed on the voltage Vb input to the integration circuit 33, the effective voltage Vrms integrated by the integration circuit 33 depends on the ripple frequency even if the voltage value is the same. There may be slight differences. Therefore, in order to measure the effective voltage Vrms of the AC voltage VAC with high accuracy, it is necessary to reliably average the voltage Vb. Specifically, when the ripple frequency superimposed on the voltage Vb is a high frequency, in order to cope with a steep voltage fluctuation of the AC voltage VAC, a high-capacity small-capacitance capacitor is used, and a low-frequency capacitor is used. Sometimes it is necessary to use a large-capacitance capacitor to ensure integration, even at the expense of some responsiveness.
[0007]
For this reason, it is necessary to switch the averaging capacitors 17 and 18 externally added to the integration circuit 33 to one of the two depending on the frequency of the AC voltage VAC output from the inverter device 2. At the time of the rotation speed (that is, when the frequency of the AC voltage VAC is low), the changeover switch 52 is operated to the on state. As a result, a high level signal is output from the inverter circuit 14, whereby the analog switch 15 is controlled to be in an ON state. As a result, the large capacity averaging capacitor 17 functions as an integration time constant of the integration circuit 33. On the other hand, when the motor M has a high rotation speed (that is, when the frequency of the AC voltage VAC is high), the changeover switch 52 is maintained in the OFF state. As a result, when the low level signal is output from the inverter circuit 14, the analog switch 15 is controlled to be turned off, and the high level signal is input to the analog switch 16 to be controlled to be turned on. As a result, the small-capacitance averaging capacitor 18 functions as an integration time constant of the integration circuit 33.
[0008]
[Problems to be solved by the invention]
However, this conventional voltmeter 51 has the following problems.
That is, in the voltmeter 51, in order to accurately measure the effective voltage Vrms of the AC voltage VAC, either the averaging capacitor 17 or 18 is operated by operating the changeover switch 52 according to the rotational speed of the motor M. It is necessary to switch to one. However, the determination of the rotational speed of the motor M differs depending on individual differences among operators, and even the same person differs depending on the determination at that time. For this reason, the conventional voltmeter 51 has problems in that the reproducibility of measurement is poor and the measurement accuracy itself is low. In addition, the changeover switch 52 must be operated according to the number of rotations of the motor M, and there is a problem that the measurement is complicated.
[0009]
The present invention has been made in view of such problems, and mainly provides a measuring apparatus capable of performing measurement with high accuracy and reproducibility by automatically following the frequency of an input signal under measurement. Objective.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the measuring apparatus according to claim 1 includes an integration circuit capable of switching the time constant, and integrates an integration target signal based on the input AC signal by the integration circuit, thereby obtaining an effective voltage for the AC signal. In a measuring apparatus that includes an effective voltage measuring unit that outputs and measures an electrical parameter for an AC signal based on the output effective voltage, a frequency measuring unit that measures the frequency of the input AC signal, and a frequency measuring unit A switching control unit that switches and controls the time constant of the integration circuit based on the measured frequency, and the integration circuit switches at least a first time constant and a second time constant having a value smaller than the first time constant. The switching control unit is configured to use a first reference frequency and a second reference frequency higher than the first reference frequency as threshold values, and When the measurement frequency is lower than the first reference frequency and higher than the second reference frequency, the control is switched to the first time constant and the second time constant, respectively, and the measurement frequency is When the frequency is between the first reference frequency and the second reference frequency, and when the frequency is lower than the second reference frequency and the frequency is between the first reference frequency and the first reference frequency, Switching control is performed between a time constant and the second time constant .
[0011]
In this measuring apparatus, when an AC signal as a signal under measurement is input, the frequency measuring unit measures the frequency of the AC signal. Next, the switching control unit switches the time constant of the integration circuit based on the measurement frequency. Thereby, the integration circuit integrates with a time constant suitable for the frequency of the ripple voltage based on the AC signal superimposed on the integration target signal. Through these processes, the effective voltage measuring unit automatically follows the frequency component of the AC signal, and measures the effective voltage of the AC signal with reproducibility and accuracy.
[0012]
In this measuring apparatus, the switching control unit performs so-called hysteresis control. That is, for example, when the measurement frequency is gradually increased from a low frequency, the switching control unit first switches the time constant of the integration circuit to a first value having a large value when the frequency is lower than the first reference frequency. Control and maintain at the first time constant until the second reference frequency is reached. Next, when the measurement frequency exceeds the second reference frequency, the switching control unit controls the switching to a small second time constant, and maintains the second time constant until the measurement frequency falls below the first reference frequency. To do. By performing switching control in this way, even when the measurement frequency fluctuates around the threshold value, variation in measurement results due to complicated switching control of the time constant of the integration circuit is ensured. Can be prevented.
[0013]
The measuring apparatus according to claim 2 is the measuring apparatus according to claim 1, wherein the integrating circuit is configured to be able to switch the time constant by switching the capacitive element, and the switching control unit includes the capacitive element of the integrating circuit. It is characterized by switching control.
[0014]
Switching of the time constant may be controlled by switching any element that forms a time constant such as a resistance element and a capacitive element. On the other hand, it is possible to reduce the size of the measuring apparatus by integrating resistance elements and semiconductor elements and switching and controlling capacitive elements as external additional elements.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which a measuring device according to the present invention is applied to a voltmeter will be described with reference to the accompanying drawings. In addition, about the component same as the voltmeter 51 which the applicant has already developed, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
[0016]
First, the configuration of the voltmeter 1 will be described with reference to FIG.
[0017]
The voltmeter 1 is used as a part of a measurement system S1 for measuring the torque characteristics of the motor M as shown in the figure, and in the same manner as the conventional voltmeter 51, an effective voltage measurement unit 11 and a calculation unit 12 are used. In addition to the display unit 13, the inverter circuit 14, the analog switches 15 and 16, the averaging capacitors 17 and 18 corresponding to the capacitive elements in the present invention, the frequency of the AC voltage VAC is measured instead of the changeover switch 52 and the like A frequency measurement unit 19 and a control unit 20 that controls switching of the averaging capacitors 17 and 18 according to the measurement frequency measured by the frequency measurement unit 19 are provided.
[0018]
For example, the frequency measuring unit 19 includes a comparator, a clock oscillator, and a counter. When the AC voltage VAC is input, the frequency measuring unit 19 generates a square wave signal having a period equal to the period of the AC voltage VAC by shaping the waveform of the AC voltage VAC using a comparator. Next, the counter counts in synchronization with the clock signal generated by the clock oscillator within one cycle of the square wave signal, and outputs the frequency data Df that is the count value to the control unit 20.
[0019]
The control unit 20 corresponds to the switching control unit in the present invention, and outputs a high level signal to one of the analog switches 15 and 16 according to the frequency of the AC voltage VAC as the measurement target signal. Specifically, the control unit 20 uses the first reference frequency Fref1 and the second reference frequency Fref2 higher than the first reference frequency Fref1 as threshold values, and the measurement frequency specified by the frequency data Df is the first. By outputting a high level signal to the analog switch 15 when the frequency is lower than one reference frequency Fref1, control is performed so that the time constant of the integrating circuit 33 is increased. On the contrary, when the measurement frequency is higher than the second reference frequency Fref2, the control unit 20 outputs a high level signal to the analog switch 16 so that the time constant of the integration circuit 33 is reduced. Further, the control unit 20 continuously outputs a high level signal to the analog switch 15 when the measurement frequency is a frequency between the first reference frequency Fref1 and the second reference frequency Fref2, thereby integrating the integration circuit. The time constant of 33 is kept large, and when the measurement frequency is a frequency between the second reference frequency Fref2 and the first reference frequency Fref1, a high level signal is continuously output to the analog switch 16. Thus, the time constant of the integrating circuit 33 is kept small.
[0020]
Next, with respect to the operation of the voltmeter 1, as shown in FIG. 3, a case where the measurement frequency gradually increases from 0 Hz to the maximum frequency and gradually decreases from the maximum frequency is described as an example with reference to FIG. explain.
[0021]
First, when the power is turned on, the control unit 20 outputs a low level and controls the analog switch 15 to be in an ON state, thereby connecting the low frequency averaging capacitor 17 to the integrating circuit 33. Next, when the AC voltage VAC is input, as shown in FIG. 2, the frequency measuring unit 19 measures the frequency of the AC voltage VAC (step 41), and outputs frequency data Df as a measurement result to the control unit 20. . At this time, the control unit 20 determines whether or not the measured frequency is higher than the second reference frequency Fref2 based on the frequency data Df (step 42). In this example, at time t1 in FIG. 3, after determining that the measurement frequency is lower than the second reference frequency Fref2, the control unit 20 determines whether or not the measurement frequency is lower than the first reference frequency Fref1 (step). 43). At time t1, since the measurement frequency is lower than the first reference frequency Fref1, the control unit 20 keeps the analog switch 15 on. Since the measurement frequency does not exceed the second reference frequency Fref2 between time t1 and time t2, the control unit 20 repeatedly executes steps 42 and 43 described above to maintain the analog switch 15 on. .
[0022]
Next, when the time t2 is reached, since the measurement frequency exceeds the second reference frequency Fref2, the control unit 20 outputs a high level signal and controls the analog switch 16 to be turned on to replace the averaging capacitor 17. Then, the high frequency averaging capacitor 18 is connected to the integrating circuit 33 (step 44). After that, since the measurement frequency is higher than the second reference frequency Fref2 between time t2 and time t3, the analog switch 16 is kept on (steps 42 and 44). At time t3, the measurement frequency is lower than the second reference frequency Fref2, but is still higher than the first reference frequency Fref1, and therefore the control unit 20 maintains the analog switch 16 in the on state (Step S3). 42, 43).
[0023]
On the other hand, when the time t4 is reached, since the measurement frequency is lower than the first reference frequency Fref1, the control unit 20 outputs a low level signal and controls the analog switch 15 to be turned on, thereby causing the averaging capacitor 18 to Instead, the low frequency averaging capacitor 17 is connected to the integrating circuit 33 (steps 42, 43, 45). Thereafter, after time t4, the analog switch 16 is kept on unless the measurement frequency exceeds the second reference frequency Fref2 (steps 42, 43, 45). As described above, the control unit 20 executes the switching control of the analog switches 15 and 16 by the hysteresis control, thereby raising and lowering the vicinity of the first reference frequency Fref1 and the second reference frequency Fref2 whose measurement frequency is the threshold value. Even in such a case, variation in the effective voltage Vrms, which is a measurement result due to complicated switching control of the time constant of the integration circuit 33, can be reliably prevented.
[0024]
Next, actual measurement of the effective voltage Vrms will be described.
[0025]
In this measurement, the effective voltage Vrms is measured in the same manner as the conventional voltmeter 51. That is, first, the absolute value circuit 31 calculates the voltage Va corresponding to the absolute value of the AC voltage VAC by analog calculation. Next, the squaring / dividing circuit 32 squares the voltage Va, and generates a voltage Vb by dividing the voltage squared by the voltage Va by the effective voltage Vrms output from the integrating circuit 33. The voltage Vb Is output to the integration circuit 33. Next, the integration circuit 33 generates an effective voltage Vrms by integrating the voltage Vb, and outputs the effective voltage Vrms to the calculation unit 12. Thereafter, the calculation unit 12 generates the measurement data DM based on the effective voltage Vrms and outputs it to the display unit 13, and the display unit 13 displays the effective voltage as the measurement result based on the input measurement data DM. To do.
[0026]
Thus, according to this voltmeter 1, the frequency measurement unit 19 measures the frequency of the AC voltage VAC, and the control unit 20 determines the time constant (the averaging capacitors 17 and 18) of the integration circuit 33 based on the frequency data Df. , Even if the ripple voltage based on the AC voltage VAC is superimposed on the voltage Vb, the integration circuit 33 is set to a time constant suitable for the frequency of the ripple voltage, It can be integrated with high response speed and high accuracy. As a result, the voltmeter 1 can automatically follow the frequency component of the AC voltage VAC, and can accurately measure the effective voltage Vrms of the AC voltage VAC with good reproducibility.
[0027]
The present invention is not limited to the configuration shown in the above-described embodiment of the present invention. For example, in the embodiment of the present invention, the voltmeter 1 has been described as an example. However, the present invention calculates an ammeter, a wattmeter, a multimeter that calculates and displays current and power based on the effective voltage Vrms. It can be suitably used for various measuring devices such as meters and recorders. In the embodiment of the present invention, the example in which the averaging capacitors 17 and 18 are switched and controlled has been described, but it is needless to say that the resistance element that determines the time constant of the integrating circuit 33 may be switched and controlled. Furthermore, in the embodiment of the present invention, the example in which two threshold values of the first reference frequency Fref1 and the second reference frequency Fref2 are used in the switching control by the control unit 20 has been described. Not limited to this, the present invention can also be applied to the case where switching control is performed by providing three or more threshold values.
[0028]
In the embodiment of the present invention, the functional blocks are used. However, by using a digital signal processor (DSP) or the like, the effective voltage measuring unit 11, the inverter circuit 14, the analog switches 15 and 16, the frequency The measurement part 19 and the control part 20 can also be comprised integrally. In such a case, the voltmeter 1 can be reduced in size by switching and controlling the averaging capacitors 17 and 18.
[0029]
【The invention's effect】
As described above, according to the measuring apparatus of the first aspect, the frequency of the AC signal input by the frequency measuring unit is measured, and the switching control unit switches and controls the time constant of the integrating circuit based on the measured frequency. The effective voltage measuring unit can automatically follow the frequency component of the AC signal, and thereby, the effective voltage of the AC signal can be measured with high reproducibility and accuracy.
[0030]
Further, according to the measuring apparatus of this, by the switching control unit performs a hysteresis control, when the measurement frequency is such that lower the vicinity threshold also is troublesome to switch the control time constant of the integration circuit Therefore, it is possible to reliably prevent variations in measurement results due to the above.
[0031]
Furthermore, according to the measuring apparatus of the second aspect , the switching control unit switches and controls the capacitive element of the integrating circuit, thereby enabling integration of a resistance element, a semiconductor element, and the like. Miniaturization can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram of a measurement system including a voltmeter according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a time constant automatic switching process;
FIG. 3 is a diagram illustrating an example for specifically explaining time constant automatic switching processing, and is a diagram illustrating a relationship of a measurement frequency with respect to time;
FIG. 4 is a block diagram of a measurement system including a conventional voltmeter.
[Explanation of symbols]
1 Voltmeter 11 Effective Voltage Measurement Unit 17 Averaging Capacitor 18 Averaging Capacitor 19 Frequency Measurement Unit 20 Control Unit 33 Integration Circuit

Claims (2)

An integration circuit capable of switching the time constant is incorporated, and an effective voltage measuring unit that outputs an effective voltage with respect to the AC signal by integrating the integration target signal based on the input AC signal by the integration circuit is provided. In a measuring device for measuring an electrical parameter for the AC signal based on an effective voltage,
A frequency measurement unit that measures the frequency of the input AC signal, and a switching control unit that switches and controls the time constant of the integration circuit based on the measurement frequency measured by the frequency measurement unit ,
The integration circuit is configured to be capable of switching at least a first time constant and a second time constant having a value smaller than the first time constant,
The switching control unit uses a first reference frequency and a second reference frequency higher than the first reference frequency as thresholds, and when the measurement frequency is lower than the first reference frequency and When the frequency is higher than the second reference frequency, the control is switched to the first time constant and the second time constant, respectively, and the measurement frequency exceeds the first reference frequency and reaches the second reference frequency. And switching control to the first time constant and the second time constant, respectively, when the frequency is lower than the second reference frequency and the frequency is between the first reference frequency and the first reference frequency. Measuring device. The integrating circuit switching of the time constant can be configured by switching the capacitive element, the switching control unit according to claim 1, wherein the controller controls switching the capacitive element of the integrating circuit Measuring device.

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