JPH0395469A - Effective value measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain an effective value quickly by obtaining a square of a sampled digital voltage value or a sampled digital current value and passing the obtained value through an LPF to extract a square root. CONSTITUTION:A voltage waveform input to an input circuit 1 is sampled at a constant sampling period by an A/D converter circuit 2 and A/D converted. Then, a multiplying means 31 of a digital signal processor 3 squares an instantaneous voltage value Vn, and the squared instantaneous voltage value (Vn)<2> is allowed to pass through an LPF 32 to obtain an (effective value)<2>. This process is performed for every sampled voltage value Vn, the result of which is fed back and added. Accordingly, this process makes it possible to gradually approach to a true value of the square root of the calculated effective value. Moreover, the obtained (effective value)<2> is extracted to obtain a square root at an extracting means 33. The obtained effective value is indicated by a display device 4. In this manner, an effective value can be obtained quickly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital sampling type effective value measuring device that digitally samples an input voltage waveform or an input current waveform and measures its effective value.

〔overview〕

The present invention provides an effective value measuring device using a digital sampling method, by squaring a sampled digital voltage value or digital current value and square rooting the value by passing it through a low-pass filter. This allows the effective value to be quickly determined even if there is a deviation.

[Conventional technology]

In a device that digitally samples an input voltage waveform or an input current waveform to obtain an effective value using an analog-to-digital conversion circuit, an error occurs when the period of the input waveform and the sampling period do not match.

To explain this with a drawing, the waveform shown in Figure 7 is ζ
The period T i n of the input waveform is the sampling period TA7D
If it is not an integer multiple of, that is, TII,≠n − T
In the case of A7I1 (n=2. 3. 4...), a fraction occurs as shown in FIG. If a fraction occurs in this way, an error will be given to the detected value of the effective value of voltage or current.

For this reason, the following methods have conventionally been used to reduce the influence of the above-mentioned fractions.

■ Sampling period TA/ of input waveform. T 1n
A method of adjusting and controlling TA/D so that = n' TA/D.

■ A method of calculating the effective value by sampling the input waveform over several cycles until T(h-n-TA/+1).

■ Sampling period TA, . A method of reducing the error by making the fraction of the period T of the input waveform extremely small.

[Problem to be solved by the invention]

However, the conventional sampling period TA. In order to adjust and control the frequency, a phase lock circuit with a large frequency variable range is required, which causes the problem that the circuit structure becomes complex and expensive.

Furthermore, in the conventional method (2), measurement cannot be performed until the input waveform and the sampling period match, so there is a problem that the measurement response time becomes long.

Furthermore, the conventional method (2) requires a high-speed analog-to-digital conversion circuit, which is expensive.

The present invention solves the above-mentioned problems, and aims to provide an effective value measuring device that can be constructed at low cost without requiring adjustment of the sampling link cycle, and that can quickly measure effective values.

[Means for solving problems]

The present invention provides means for sampling an input voltage waveform or current waveform and converting it into an analog-to-digital value, means for squaring the converted digital voltage value or daisicle current value and sequentially integrating the squared values, and integrating the integrated voltage value or An effective value measuring device comprising: means for calculating an effective value from a current value; It is characterized by comprising means for feedback-adding the output to the input side, and arithmetic means for square rooting the value passed through the low-pass filter.

[Effect]

The input voltage waveform or current waveform is sampled by the analog daisicle conversion circuit at regular sampling intervals, and the voltage value or current value (instantaneous value) converted into a daisicle signal is subjected to the following arithmetic processing by the arithmetic circuit. .

The arithmetic circuit first calculates the square of the digital voltage value or digital current value. Then, the square value of this digital voltage value or digital current value is passed through a digital low-pass filter, and the output is fed back to the input side and added. When a predetermined number of sampling values are passed through a low-pass filter and the value is square rooted to obtain an effective value, asymptotically approaches the true value of the effective value by integrating multiple samplings. Extract and display as .

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of one embodiment of the present invention. In this embodiment, a configuration will be described in which the voltage waveform is sampled and the effective value is measured.

The structure and operation of sampling the current waveform and measuring the effective value are the same, and the explanation thereof will be omitted because it is sufficient to replace the voltage with the current.

The effective value measuring device of this embodiment includes an analog-to-digital conversion circuit 2 as a means for sampling an input voltage waveform and converting it into an analog-to-digital value, and a digital voltage value converted by the analog-to-digital conversion circuit 2 to be squared and sequentially In an effective value measuring device equipped with a means for integrating and a digital signal processor 3 as a means for calculating an effective value from the integrated voltage value, a low pass through which the squared value of the analog-to-digital converted digital voltage value passes. It is characterized by comprising a filter (LPF) 32, an adder 34 as a means for feeding back and adding the output of the low-pass filter means to the input side, and a square root means 33 for square rooting the value passed through the low pass filter. .

The effective value measuring device of this embodiment includes an input circuit 1 into which voltage is input, and a voltage waveform input to this input circuit 1 at a constant sampling period TA/. an analog-to-digital conversion circuit 2 that performs analog-to-digital conversion into a digital voltage value by zumbling, and a digital signal processor (DSP) 3 that performs arithmetic processing, which is a feature of the present invention.
It also includes a display device 4 that displays the determined effective value VRitS.

The digital signal processor 3 includes a multiplier 31 that calculates the square of a sampled digital voltage value (instantaneous value), a digital low-pass filter (L P F) 32 that passes the multiplied voltage value, and a low-pass filter 32 that passes the multiplied voltage value. , and an adder 34 that feeds back and adds the value that has passed through the low-pass filter 32 to the input side.

Note that, instead of the digital signal processor 3, a microprocessor or other various arithmetic processing devices that perform arithmetic processing can be used.

Next, the operation of this embodiment will be explained with reference to FIGS. 2 and 3. FIG. 2 is a flowchart showing the operation of this embodiment, and FIG. 3 is a waveform diagram explaining the operation of this embodiment.

The voltage waveform input to the input circuit 1 is sampled at a constant sampling period T A/D in the analog-to-digital conversion circuit 2 and converted into an analog-to-digital signal (step S).
l). FIG. 3(a) shows how the input voltage waveform is sampled.

Next, the instantaneous voltage value Vh is squared by the multiplication means of the digital signal processor 3 (step S2).

The squared voltage value (Vゎ)2 is shown in FIG. 3(b).

Next, the calculated instantaneous voltage value (Vh) 2 is passed through a low-pass filter 32 (step S3). This instantaneous voltage value (
V. By passing >2, is calculated (step S4). Then, the process of steps S2 to S4 is performed using the sampled voltage value V. , and perform feedback addition. It can be seen that through this process, as shown in FIG. 3(C), the calculated effective value gradually approaches the true value of the square.

Further, the effective value (to be determined) is square-rooted by the square root means 33 to obtain the effective value (step S5), and the effective value VRMS is displayed on the display device 4 (step S6).

Next, the characteristics of the calculation starting point in this embodiment will be explained.

As shown in FIG. 4(a), when sampling an input voltage waveform in which the calculation start point for the input voltage waveform changes, the true value of the square of the above-mentioned effective value can be obtained.

On the other hand, as shown in FIG. 4(b), at the calculation start point, the input voltage V is "0", and this input voltage I
V. When the time for =0 is very long, even if the input voltage is no longer "0", the effective value does not increase immediately and does not respond until a long time has elapsed. Therefore, in this embodiment, by passing the signal through the low-pass filter 32, the calculation start point is set to the point where the input voltage waveform changes.

Therefore, until the input voltage waveform changes, the display of the effective value is "zero" as shown in FIG. 4(C), and calculation is started only after the input voltage waveform starts to change.

The time required until the effective value VRMS converges to the true value by calculating the effective value VRMS according to this embodiment will be explained.

The constant of the low-pass filter 32 is set to 0. 0005, when the sampling period is 10 kHz and the input signal frequency is the frequency for the quotient q 10 (50 to 400 Hz>), it is approximately 3
The true value of the effective value is 0.0000 times (approximately 3 seconds) by the number of samplings. It converges to 707. Note that the number of samplings required for this convergence varies greatly depending on the constant of the low-pass filter 32 and the input signal frequency.

The following table shows specific numerical values of the effective values obtained for the number of samplings.

(Hereinafter, this page margin) Examples of measurements of effective values according to the present invention obtained by simulation are shown in FIGS. 5 and 6.

This simulation speeds up the convergence to the true value, so
The input signal frequency and sampling frequency are faster than those that sample commercial frequencies.

FIG. 5 shows sampling periods TA, . is not an integral multiple of the period T i n of the input waveform, but a fraction occurs, and a sine wave is used as the input waveform, and the input signal frequency is set to 97
．． 087379-. kHz (106/10.
3 Hz), input signal amplitude 1. OV(P-P)
This is an example in which the sampling period is IMHz. It can be seen that in this simulation as well, it takes about 29 ms to converge to the true value in about 3 seconds when performed at a commercial frequency.

FIG. 6 is an example in which sampling does not produce fractions, where the input signal period is 333.33kHz (3 samples in one period), and the input signal amplitude is 1.33kHz (3 samples in one period). O V (P-P),
This is an example in which the sampling period is lMl{z.

It is understandable that in this case as well, it is possible to converge to the true value in about 29 ms.

〔Effect of the invention〕

As described above, even if there is a discrepancy between the period of the input waveform and the sampling period, the present invention can quickly measure the effective value without requiring adjustment of the sampling period, and the device can be manufactured at a low cost. This has the effect of realizing an effective value measuring device that can be configured as follows. Further, since an existing low-pass filter can be used, there is an advantage that a special arithmetic circuit for integrating digital voltage values or digital current values is not required, and the structure can be constructed at low cost.

Furthermore, it has the effect of being able to measure the effective value in response to changes in the input waveform.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention. FIG. 2 is an operational flowchart of the embodiment. FIG. 3 is a waveform diagram illustrating an embodiment. FIG. 4 is a diagram illustrating the calculation starting point of the embodiment. FIG. 5 and FIG. 6 are diagrams showing simulation results for determining effective values according to the example. FIG. 7 is a waveform diagram when there is a l3 14 deviation between the input waveform and the sampling period. DESCRIPTION OF SYMBOLS 1... Input circuit, 2... Analog decile conversion circuit, 3... Digital signal processor, 4...
- Display device, 31... Multiplying means, 32... Low pass filter, 33... Square root means, 34... Adder.

Claims (1)

[Claims] 1. Means for sampling an input voltage waveform or current waveform and converting it from analog to digital; means for squaring the converted digital voltage value or digital current value and sequentially integrating the converted digital voltage values or digital current values; An effective value measuring device comprising: means for calculating an effective value from a voltage value or a current value; An effective value measuring device comprising: means for feeding back and adding the output of the filter means to the input side; and calculating means for square rooting the value passed through the low-pass filter.