JPS6023309B2 - Effective value measuring device - Google Patents

Description

[Detailed description of the invention] The present invention relates to an effective value measuring device.

Various methods have been considered for measuring the effective value of an alternating signal.

Generally, a method is widely used in which a signal to be measured is supplied to a heater Z and the heat generated by the heater is measured using a temperature sensing element such as a thermocouple. However, there are drawbacks such as a large time delay due to the use of a heater, poor accuracy due to the use of a sensitive element, and a large influence by ambient temperature.
For this reason, an effective value measuring device using a triangular wave has been considered, as shown in, for example, Journal of the Institute of Electronics and Communication Engineers, January 1976, Vol. 159-1C No. Figure 1 shows the ``digital effective value voltmeter with a wide operating range'' published in this journal. In FIG. 1, 1 is a signal input terminal to be measured, and 2 is a triangular wave input state. The nuclear measurement signal and triangular wave supplied to these input terminals 1 and 2 are folded back to the negative and positive sides by absolute value converters 3 and 4, respectively, to obtain absolute value signals. That is, in this example, the signal to be measured Vi touches the zero line and returns to the negative side, the triangular wave touches the zero line and returns to the positive side, these absolute value signals are added in the adding circuit 5, and the added value is passed through the reduction filter. The voltage to be measured is V at the output of this filter 6.
A DC voltage corresponding to the root mean square value of i is obtained. This DC voltage is sent to the voltage-to-frequency converter 7, which converts it into a frequency signal, and the frequency output is sent to the counter 8.
and the counting output is sent to the digital-to-analog converter 9.
The converted signal is converted into an analog signal by the filter 10, and then fed back to the voltage frequency converter 11 through the reduction filter 10, where it is converted into a frequency signal and a part of the converted output is sent through the frequency divider 12 to the reset terminal of the counter 8. let them return. With this configuration, the frequency output from the voltage-frequency converter 11 is proportional to the square root of the frequency combined with the counter 8, and when this frequency is measured by the frequency counter 13, the effective value of the lamp pressure Vi to be measured is obtained. can be displayed digitally.
According to this effective value measuring device, the signal to be measured Vi is averaged over two samples using a triangular wave, and the effective value is obtained from the root mean value of the two signals.Therefore, there is no time delay and the accuracy is higher than when using a temperature sensing element. Effective values can be measured well.

Next, the reason why the effective value of the signal under measurement can be obtained using a triangular wave will be explained. First, when the input voltage is positive or negative, if it is negative, it is always folded back to the positive side in the absolute value circuit (in the circuit shown in Figure 1, it is folded back downwards due to polarity), and any measured signal is Consider f(t).

When adding a triangular summation wave having a negative voltage to this and extracting a positive voltage from the result, the shaded area in FIG. 2 is obtained. In this case, the apex angle of the hatched triangle deviates from 8 as the value 8 of the added triangular wave increases.

And fo < f (W is the frequency of the triangular wave, f is the input wave f (
t), the input waveform appears at its output. Therefore, it is desirable to set fo>f. The above operation is equivalent to subtracting a positive triangular wave from the input wave. Therefore, when drawing as shown in FIG. 3, the shaded area has the same area as the shaded area in FIG. In FIG. 3, the signal to be measured having a repetition frequency T is cut out by a triangular wave having a constant angle 8. In this case, consider a minute region ΔS having the same phase relationship in the input waveform.

The probability P that this region is cut out by the above triangular wave will approach 1 as △S approaches the peak of the triangular wave if the signal to be measured and the addition triangular wave are not synchronized, and decrease to 0 as it approaches zero potential. It can be seen that the probability P of ΔS being close and Vp>V>0 changes in proportion to V. Therefore, P can be expressed as a function of V as P(V)=temperature [11].

In this), Vp is the peak value of the addition triangular wave. If the signal under measurement is cut out as shown in Figure 3 over a sufficiently large number of cycles, and the average value (DC component) of the shaded part is Vo, this means that each point of the input waveform has a probability density given by the first equation. If you have one, integrate it over one period and get the same value as the average value.

Therefore v.

Drought damage P(V)△S ■If △S is made sufficiently small V.

=≠′ and ′ are both p(V)・dV・dt [31If you calculate by inserting the first equation into this, you will get v.

= history; field f2(t)●dt '4) is obtained. This result holds true in the range of 180o>0>oo in FIG. Therefore, regardless of the frequency of the summing triangular wave (or the frequency of the signal under test if 0 is constant), the average value (DC component) of the output voltage of the triangular wave root-mean-square circuit is equal to two times the instantaneous value f(t) of the signal under test. It shows that it is proportional to the average value of.
By using a triangular wave in this way, a DC voltage proportional to the effective value of the alternating signal can be obtained from an electric circuit, but as mentioned above, it is better if the period of the triangular wave and the period of the input wave are not synchronized.

This invention attempts to prevent the input wave and the triangular wave from being synchronized by changing the period of the triangular wave irregularly.

FIG. 4 shows an embodiment of the invention. In Figure 4, 1
4 indicates a triangular wave generator, and the other configurations are exactly the same as those in FIG. 1. That is, in this invention, the period of the triangular wave outputted from the triangular wave generator 14 is changed irregularly. For this purpose, a voltage generator 15 that changes irregularly is provided, and a voltage that changes irregularly is applied from this voltage generator 15 to an integrator 14b constituting the triangular wave generator 14.

In other words, the triangular wave generator 14 includes the integrator 140 and the voltage comparator 1.
4a, and the output voltage of the integrator 14b is compared with, for example, a common potential by a voltage comparator 14a. Therefore, if the output voltage of the integrator 14b, that is, the integrated voltage, is a negative voltage, the output of the voltage comparator 14a will be a negative voltage. Therefore, the integrator 14b integrates the negative voltage, and its output flea pressure gradually increases in the positive polarity direction. When the output of the integrator 14b exceeds the fin level of the common potential point and becomes a positive voltage, the output of the comparator 14a is reversed to a positive voltage, the direction of integration of the integrator 14b is reversed, and the output voltage of the integrator 14b is gradually decreases. A triangular wave is generated by this repetition, and in this embodiment, switches Q, . Q
2, the irregularly changing voltage is added to the input voltage of the integrator 14b. For this purpose, first, a positive bias voltage is applied to the cathode of, for example, the Zener diode D through the resistor R.
, can be maintained at a constant pressure. Jenner diode D
, and the resistor R, take out the white noise generated by the Jenner diode D, through the capacitor C, and amplify this white noise as necessary, and supply it to the capacitor C2 through the switch Q. . Switches Q and Q2 can each use field effect transistors, and an inverter 17 is connected to the gate of switch Q.
The output of the voltage comparator 14a is supplied through the voltage comparator 14a. Therefore, the switch Q is turned on when the output of the voltage comparator 14a is a negative voltage, and turned off when the fin pressure is positive. Therefore, when the integrator 14b reverses from a state in which it integrates a negative voltage to a state in which it integrates a positive voltage, the level of the white noise immediately before this is stored in the capacitor C2. The voltage stored on capacitor C2 is applied through buffer multiplier 18 to switch Q2. Switch Q2 operates inversely to the operation of switch Q. Therefore, the switch Q2 is turned on while the integrator 14b is integrating the positive voltage, and adds the voltage stored in the capacitor C2 to the input of the integrator 14b through the resistor R2. The voltage stored in capacitor C2 is based on white noise and therefore varies irregularly. Therefore, the integrator 14b
The integration period of the positive voltage changes depending on the voltage value added through the switch Q2, and the period can be changed irregularly. If V is supplied to the triangular wave input terminal 2 of the rms value measuring device for the triangular wave obtained in this way, the period of the input wave and the triangular wave will be the same no matter what frequency the signal under test supplied to the input terminal 1 has. are never synchronized and a highly accurate effective value can always be obtained.

FIG. 5 shows another embodiment of the invention. In this example, a case is shown in which the effective value measuring device is constituted by a pair of root mean square value circuits 19 and 20 and a subtraction circuit 21 for obtaining a deviation value of the outputs of these root mean square value circuits 19 and 20. That is, it has two input terminals a and b, a triangular wave is supplied to one of these two input terminals a and b, and the triangular wave and the signal supplied to the other input terminal are added through resistors R3 and R4, and the sum value is By finding the absolute value of and taking it out through a reduction filter, the root mean square value of the signal supplied to the other input, that is, the signal under test supplied to input terminal 1, for example, and the output of the arithmetic circuit 21 is obtained. The plan average value is taken out by resistors R5 and R6, the deviation between the outputs of the two plan average value circuits 19 and 20 is determined by the arithmetic circuit 21 constituted by a differential amplifier, and the deviation value is applied to the two plan average value circuits. On the other hand, in this case, a voltage proportional to the effective value of the input wave V supplied to the input terminal 1 can be obtained from the output of the arithmetic circuit 21 by feeding it back to one input terminal b of the input terminal 20. In this way, the pair of root mean square value circuits 19 and 20 calculate the two average values of the input wave and the output of the arithmetic circuit 21, and by subtracting the root mean value, the components of the triangular wave are canceled out. Therefore, even if the amplitude of the triangular wave fluctuates, no error occurs in the measured value. In other words, according to the effective value measuring device explained in Figs. 1 and 4, only the input wave is averaged by the triangular wave, so if the amplitude of the triangular wave fluctuates, the average value of the two designs also fluctuates, resulting in measurement error. may occur.

Therefore, according to the embodiment of FIG. 5, the triangular wave component is
1, so even if the amplitude of the triangular wave fluctuates, there is no risk of giving an error to the measured value, and highly accurate measurement can be performed.

However, the voltage generator 1 which changes irregularly in the triangular wave generator 14
By adding 5 and irregularly changing the period of the output wave of the triangular wave generator 14, it is possible to measure the effective value with higher accuracy regardless of the frequency of the input wave. In the above description, the triangular wave generator 14 is replaced by the voltage comparator 14a and the integrator 14.
b, but the configuration is not limited to this. In addition, as a means for irregularly changing the period of the output wave, a voltage generator 15 that generates an irregularly changing voltage is added, but other means for irregularly changing the period of the triangular wave can be considered. can be easily understood.

[Brief explanation of the drawing]

Fig. 1 is a system diagram for explaining a conventional effective value measuring device, Figs. 2 and 3 are waveform diagrams for explaining the operation of the effective value measuring device shown in Fig. 1, and Fig. 4 is a system diagram for explaining the operation of the conventional effective value measuring device. FIG. 5 is a system diagram showing one embodiment of the invention. FIG. 5 is a system diagram showing another embodiment of the invention. 14... Triangular wave generator, 15... Voltage generator whose voltage changes irregularly. Figure Iso trunk Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] 1. In an effective value measuring device that uses a triangular wave to obtain the root mean square value of the signal under test and uses the root mean square value to obtain the effective value of the signal under test, the period of the triangular wave is irregularly varied. An effective value measuring device.