JPS6023308B2 - 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 widely used method is to supply a signal to be measured to a heater and measure the heat generated by the heater 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 temperature sensing element, and a large influence by ambient temperature. For this reason, for example, the Transactions of the Institute of Electronics and Communication Engineers, January 1978, VoL591, CM. As shown in 1, an effective value measuring device using a triangular wave has been considered.

Figure 1 shows the ``digital effective value voltmeter with a wide operating range'' published in this journal. In Figure 1, 1
2 is a signal input terminal to be measured, and 2 is a triangular wave input terminal. The signal to be measured and the triangular wave supplied to these input terminals 1 and 2 are returned to the negative and positive sides by absolute value circuits 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. Hirai boar at evening 6, this fill evening 6
A DC voltage corresponding to the root mean square value of the voltage to be measured Vi is obtained at the output. This DC voltage is supplied to a voltage-to-frequency converter 7, which converts it into a frequency signal, whose frequency output is counted by a counter 8, and whose counting output is converted into an analog signal by a digital-to-analog converter 9. It is supplied to the voltage frequency converter 11 again through the reduction filter 0, where it is converted into a frequency signal, and a part of the converted output is fed back to the reset terminal of the quanta 8 through the frequency divider 12. With this configuration, the frequency output from the voltage-to-frequency converter 11 is proportional to the square root of the frequency supplied to the counter 7, and when this frequency is measured by the frequency counter 13, the effective value of the signal under measurement Vi can be digitalized. can be displayed. According to this effective value measuring device, the square mean of the signal to be measured Vi is calculated using a triangular wave, and the effective value can be measured more accurately than when using a temperature sensing element without time delay.

However, there is a major drawback in that when the peak level of the triangular wave fluctuates, the average value of the two signals Vi obtained from the reduction filter 6 fluctuates. Furthermore, the scale of the opening/closing arithmetic circuit becomes large, which increases the number of error factors, and there is also the drawback that an attempt to increase accuracy results in a high value. Furthermore, since the final output is a frequency, a frequency counter is required, which also requires a time reference, and the accuracy of the time reference becomes a factor of error. The first object of the present invention is to prevent measurement errors from occurring even if the peak level of the triangular wave changes in an effective value measuring device that obtains the effective value of the signal under test using a root mean square value circuit using a triangular wave. The goal is to provide an effective value measurement device that does not.

A second object of the present invention is to provide an effective value measuring device that can accurately measure the effective value of the signal under test Vi even if the level of the signal under measurement Vi fluctuates greatly.

A third object of the present invention is to provide an effective value measuring device that can be provided at a low price.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a system diagram showing an outline of the effective value measuring device according to the present invention.

The present invention comprises a pair of two-way average value circuits 14 and 15 that output the two-way average value of the signal under test using a triangular wave, and a subtraction circuit 16. A pair of two-plan average value circuits 14 and 15 each have the same configuration and two input terminals 17 and 18, and supply a triangular wave signal to one input terminal and a signal to the other input terminal and add the signal. The circuit configuration is such that the absolute value of the signal under test is determined and the root mean square value of the signal under test is outputted through a reduction filter. That is, one input terminal 17 of the root mean square value circuit 14 is connected to the input terminal 1 of the signal under test Vi, and the other input terminal 18 is connected to the triangular wave input terminal 2. Further, one input terminal 17 of the mean square value circuit 15 is connected to the triangular wave input terminal 2, and the output of the subtraction circuit 16 is fed back to the other input terminal 18, and the output is led out to the output terminal 19. The subtraction circuit 16 can use, for example, a differential amplifier and is required to have a large gain. According to the above-described configuration, the root mean square value circuit 14 obtains the sum of the two-way average value of the signal under test Vi and the average value of the triangular wave.

Further, the root mean square value circuit 15 obtains the sum of the root mean square value of the output of the subtraction circuit 16 and the average value of the triangular wave. Therefore, since the two two-way average values supplied to the input of the subtraction circuit 16 both contain triangular wave components, the triangular wave components are canceled out in the subtraction circuit 16. Therefore, even if there is a fluctuation in the triangular wave component, the output voltage Vo of the subtraction circuit 16 does not fluctuate.
Therefore, it is possible to perform measurements that are not affected by level fluctuations of the triangular wave component. Next, it will be explained that the output voltage Vo of this circuit is equal to the effective value of the signal under test Vi.

That is, the root mean square value circuits 14 and 15 apply the fact that the area of similar triangles is proportional to the square of the height, and as shown in FIG. 3, the input signal f(t) and the positive and negative peak values are equal. By adding the triangular waves, a waveform having the area of the hatched portion shown in the figure can be obtained. In this case, consider a small area ΔS that has the same phase relationship as the input signal f(t). This area △S
The probability P that is included in the triangular wave is the zero line 0 of the tiny area △S, unless the input signal f(t) and the triangular wave are synchronized.
P(u) = pair as a function of position u from 10
'1).

(However, u must be included within 2Vp) This means that each point of the input signal Vi has a probability density given by equation '11. If the average value is obtained by integrating over one period, the value obtained by averaging the shaded portion over a number of periods will be the same. In other words, the character SP(u)△S: 嬬さ. Phantom...P(u
)△u・△t
{2, The shaded area is divided into a positive part and a negative part from the zero line 010.

Let Vo be the average value of the sum of the positive part and the negative part. Vo = average value of the positive part + average value of the negative part 1,000 degrees)
2 magazine center dt cross skin 3p side 2 bed du. dt=point; zhi [vP
H (t)] 2 sail ≠' Samo [vP-f (t)] 2 dt = Hirohada vP 10 etc} dt [3' {3-If you subtract the triangular wave component from the equation, v.

= Taizo J; [f(t)]2dt [41, and the output of the subtraction circuit 16 becomes a value proportional to the root mean square value of the input signal f(t). Therefore, the system diagram shown in FIG. 2 can be rewritten into the system diagram shown in FIG. 4. As shown in FIG. 4, the 2-way average value circuit 14 obtains the square mean value Vi2 of the signal under test Vi, and the 2-way mean value circuit 15 provides the subtraction circuit 1.
An average value Vo2 of the two output voltages Vo of No. 6 (Vo is a DC voltage) is obtained. Therefore, if the gain of the subtraction circuit 16 is A, then 11 [51V
o=(Vi2-Vo2)AV.

=-...If the gain A of the Vi2 subtraction circuit 16 is set sufficiently large, 11 '6'
Vo≠±Vi2, and Vo can obtain the effective value of Vi by taking either (10) or (1) in the circuit.

FIG. 5 shows a specific embodiment of this invention.

In the figure, 20 indicates a triangular wave generator, and the triangular wave outputted from this is supplied to the input terminal 2, and together with the signal under test Vi supplied to the input terminal 1, the input terminals 17 of one and the other of the mean square value circuit 14 and 18. Input terminal 17
The signal to be measured Vi and the triangular wave supplied to and 18 are connected to the resistor R.
4 and R5, and the added value is added to the operational amplifier A.
It is supplied to the inverting input terminal of No. 3. An absolute value circuit is formed by the diodes D, D2 and feedback resistors R6 and R7 to the operational amplifier, and the output thereof is connected to the averaging circuit, that is, the reduction filter formed by the feedback capacitor C2 and the feedback resistor R9 to the operational amplifier. It is supplied in the evening. The two plan average value circuits 15 are also constructed in the same way, and these two plan average value circuits 14
The outputs of and 15 are supplied through resistors R, 5 and R, 9 to a subtraction circuit 16 constituted by a differential amplifier, and the subtraction output is supplied to the base of an emitter-floor transistor Q through a wide diode.

Therefore, the emitter of transistor Q, ie, the output terminal 1 9
One sacrificial effective value is obtained by the diode D5. By the way, in the above description, the oscillation of the triangular wave was considered to be fixed. However, as explained earlier, the minute area △S
is required to always be included within the oscillation of the triangular wave. Therefore, if the amplitude of the signal to be measured Vi increases and exceeds the amplitude of the triangular wave, an error will occur in the measured value. For this reason, it is possible to set the amplitude of the triangular wave sufficiently large in advance so that the amplitude of the signal under test Vi does not exceed the amplitude of the triangular wave, but if the amplitude of the signal under measurement Vi has a small value, The ratio of the triangular wave to the oscillation becomes large, and this also causes a large error. After all, it is ideal that the amplitude of the signal to be measured Vi and the amplitude of the triangular wave should always match. FIG. 6 shows an embodiment for this purpose.

In this example, the first peak value detection circuit 21 detects the peak value of the signal under test Vi, and the first peak value detection circuit 21 detects the peak value of the triangular wave.
A peak value detection circuit 22 is provided, the detection outputs of these peak value detection circuits 21 and 22 are compared in a peak value comparator 23, and the gain of the gain control circuit 24 is controlled by the comparison output, and the triangular wave generator 20 A case is shown in which the peak value of the triangular wave output from the signal Vi is controlled so as to be always equal to the peak value of the signal under test Vi. This configuration has the advantage that even if the level of the signal under test Vi changes greatly, it can always be measured in the best condition and the dynamic range can be widened.

FIG. 7 shows a specific example thereof.

In the figure, the peak value of the signal to be measured Vi is held in a capacitor C6, and the peak value of the triangular wave is held in a capacitor C8. The peak value of the signal under test Vi held in these capacitors CG and C8 and the peak value of the triangular wave are supplied to the differential amplifier constituting the comparator 23, and the deviation value is supplied to the gain control circuit 24, which outputs the triangular wave. The peak value is controlled to be equal to the peak value of the signal under measurement. In this example, the output of the comparator 23 is supplied to the light emitting diodes D, 2, and the resistance value of the photoelectric conversion element C is changed depending on the amount of light emitted from the light emitting diodes D, 2. This shows the case where the child is changed. In this way, the triangular wave output from the triangular wave generator 20 is transmitted to the gain control circuit 2.
4, it is controlled to have the same amplitude as that of the signal under test Vi, and is supplied to the two average value circuits 14 and 15.

Therefore, according to this embodiment, the relationship between the oscillation of the signal under test Vi and the oscillation of the triangular wave is always in the best condition, and accurate measurements can be made. As explained above, according to the present invention, a triangular wave is supplied to the pair of root mean square value circuits 14 and 15, and one side obtains the root mean square value of the signal under test Vi, and the other side obtains the root mean square value of the signal under test Vi. Since the two-way average value of the deviation value of the output of the Hata average value circuit is obtained, and these two-way average values are subtracted by the subtraction circuit 16, the triangular wave components are canceled in this subtraction circuit, so that the amplitude of the triangular wave is Even if the inside changes, there is no risk of causing an error in the measured value, and it is possible to measure the effective value with high accuracy.

Further, in the present invention, the output terminal 19 can obtain a road current separation pressure proportional to the effective value of the signal to be measured Vi, so this output voltage can be read with an analog voltmeter, or can be read with a digital voltmeter. A display type effective value measuring device can be provided.

[Brief explanation of the drawing]

Figure 1 is a system diagram for explaining the previously proposed effective value measuring device using a triangular wave, Figure 2 is a system diagram for explaining the outline of the effective value measuring device according to the present invention, and Figure 3 4 is a simplified system diagram for explaining the operation of the device of the present invention shown in FIG. 2. FIG. FIG. 6 is a system diagram showing another embodiment of the invention, and FIG. 7 is a connection diagram showing the specific embodiment. 1... Measured signal input terminal, 2... Triangular wave input terminal, 14, 15... Root mean square value circuit, 16... Subtraction circuit, 19 ...Output terminal, 20...Triangular wave generator, 21, 22...
...Peak value detection circuit, 23...Comparator, 2
4...Gain control circuit. Figure 2: Drilling Figure 4 Figure 6 Figure 7

Claims (1)

[Claims] 1. A pair of root mean square value circuits for obtaining the root mean square value of a signal supplied to one input terminal of a triangular wave and supplied to the other input terminal; and a subtraction circuit for obtaining the deviation value of the output, and supplies a triangular wave having positive and negative symmetrical peak values to one input terminal of each of the pair of root mean square value circuits, and calculates the root mean square value. An effective control device characterized in that the signal under test and the output of the subtraction circuit are fed back to the other input terminal of the circuit, and a DC voltage corresponding to the effective value of the signal under test is obtained from the output of the subtraction circuit. Value measuring device. 2. A pair of root mean square value circuits in which a triangular wave is supplied to one input terminal and the root mean square value of the signal supplied to the other input terminal is obtained, and a deviation value of the output of the pair of root mean square value circuits is obtained. It is equipped with a subtraction circuit, a circuit for detecting a level change of the signal under test, and a variable gain control circuit for changing the amplitude of the triangular wave supplied to the pair of root mean square value circuits based on the output of the detection circuit. The triangular wave obtained from the variable gain control circuit is supplied to one input terminal of each of the pair of root-mean-square value circuits, and the signal under test and the above-mentioned signal are supplied to the other input terminal of each of the pair of root-mean-square value circuits. An effective value measuring device, characterized in that the output of a subtraction circuit is supplied, and the effective value of a signal under test is obtained from the output of the subtraction circuit.