JPH04105073A - Measuring device for effective value - Google Patents

Abstract

PURPOSE:To enable quick measurements to be taken with less expensive constitution by digitizing the sampling value of a measured signal during a certain period, and squaring or exponentially averaging the digitized value or extracting the square root thereof. CONSTITUTION:The instantaneous value Bn of a measured signal B at a terminal P1 is sampled in an S/H (sample/hold) circuit 1, and digitized with an ADC (A/D converter) 2. In addition, the square of the instantaneous value Bn is outputted from a square computing element 6. Thereafter, the outputted value is exponentially averaged with an exponential average computing element 7. Furthermore, the effective value of the signal B is outputted from a square root extraction computing element 8. According to the aforesaid construction, the period of the waveform of the signal B can be measured, independent of the multiple of a sampling period, and measurement and control circuits related to the period can be eliminated, thereby allowing cost reduction. Also, it is unnecessary to make computation until the integral multiple of the half-period of an input waveform agrees to the integral multiple of the sampling period, thereby preventing the occurrence of a long measurement response time.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a digital sampling type effective value measuring device that digitally samples a signal under test (input voltage or input current) and measures its effective value. It is.

<Prior art> In a device that uses an analog/digital conversion circuit to digitally sample a signal under test and determine its effective value, an integer multiple of a half cycle of the signal under test waveform does not match an integer multiple of the sampling period. An error occurred in some cases.

This will be explained using drawings. Effective value Bn of signal under test B: Represented by a sampling value of the signal under test. Here, if the signal under test B is a voltage signal,
Bn is the sampling voltage value, and if it is a current signal,
This is the sampling current value.

As in the waveform shown in FIG. 5, when the half period of the signal under test waveform is not an integral multiple of the sampling period TAD, that is, nl·T,/2'! 'tn2- To T〇n n1=1.2,3゜n2=2.3,4. ...Tin: In the case of the period of the measured signal waveform, a fraction occurs as shown in FIG. When a fraction occurs in this way, this fraction is equal to the average value of equation (1) (a F
, Bn). In other words, the effective value BRH
3 will give an error.

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

■ The sampling period TAD of the input waveform is nl・T−/
2=n2・TAD n A method of adjusting and controlling AD.

■ Until rll-T, /2=n2-TAo,
A method of calculating the effective value by sampling the input wave + n over several cycles.

(2) A method of reducing the error by shortening the sampling period TAD and making the fraction of the period Tio of the input waveform extremely small.

<Problems to be Solved by the Invention> However, the conventional methods (1) to (3) above each have the following problems.

Method (2) requires a phase lock circuit with a wide frequency variable range for adjusting and controlling the sampling period TAD. Therefore, the circuit configuration becomes complicated,
There is also the problem that it is expensive.

Method (2) has the problem that measurement response time becomes long because measurement cannot be performed until n integral multiples of the half period (T, /2) of the input waveform and integral multiples of the sampling period TAD/) match.

The method (2) requires a high-speed analog/digital conversion circuit that can process sampling data that is taken in one after another in a short cycle, which poses the problem of being expensive.

An object of the present invention is to solve the above-mentioned problems, and to provide an effective value measuring device that does not require adjustment of the sampling period, can be constructed at low cost, and can quickly measure effective values.

Means for Solving the Problems> In order to solve the above problems, the present invention provides AD conversion means (1, 2) that samples an analog signal under test at a certain period and converts this sampling value into a digital signal. , a squaring calculator (6) for squaring the digital output signal of this AD conversion means, and an exponential averaging calculator (7) for introducing the squared data and performing an exponential averaging operation on it. ), and a square root calculator (8) which introduces the output of this exponential averaging calculator and performs a square root calculation.

Function> The AD conversion means samples the analog signal under test at a certain period and converts it into a digital signal. Therefore, the AD conversion means converts the instantaneous value (an) of the signal under measurement (B) into
It imports and outputs this.

The squaring unit performs squaring on the digital output signal of the AD conversion means. Therefore, the square calculator outputs the square value (Bn) of the instantaneous value of the signal under measurement.

The exponential average calculator introduces squared data,
Since an indexed average calculation is added to this, by performing the predetermined number of calculations, the indexed average value of an, that is, 1''' - ΣBn is obtained.

″′L mochi 1 Effective value can be obtained.

<Example> Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing a configuration example of an effective value measuring device according to the present invention, FIG. 2 is a diagram showing signal waveforms of each part of the device in FIG. 1, and FIG.
FIG. 4 and FIG. 4 are diagrams showing measurement data and display timing.

In FIG. 1, the signal under test B applied to the terminal P1 may be a voltage signal e or a current signal i, and the device in FIG. 1 is a device for measuring the effective value of this voltage e or current i. It is.

The analog signal under test B applied to terminal P1 is (second
(see waveform in FIG. 1)) and is guided to a sample-and-hold circuit (hereinafter simply referred to as an S/8 circuit) 1.

The S/8 circuit 1 receives the clock signal S from the tarock generator 3.
Each time C is added, the instantaneous value 8(t) of the signal under measurement B at that time is sampled, and the newly captured value is output in place of the value captured in the previous sampling. The black circles in FIG. 2(1) indicate each sampling point. Note that t means the number of samplings, and t=1.2.3... And B(1)-B
1.8(2)=82. ...B(n)=Bn.

An analog-to-digital converter (hereinafter simply referred to as ADC) 2 takes in the analog output signal of the S/H circuit 1, and
Convert this to a digital signal (such conversion is described below as
(simply referred to as AD conversion). When a start signal SD obtained by delaying the tarok signal SC is applied, the ADC 2 starts from the time when this signal SO is applied.
The signal applied from the /H circuit 1 is converted into a digital signal and output. Therefore, in the n-th sampling, the instantaneous value Bn is output (see FIG. 1). The AD conversion means not described in the claims refers to this S/H circuit 1 and the AD conversion means.
Consists of C2.

Note that when the current i is the signal under test B, this current i
is converted into a voltage signal ν1 and applied to the terminal P1.

I will add an explanation to this. When a current to be measured i is passed through a shunt resistor R5 (not shown) whose resistance value is known, a voltage ν1
=R3-i occurs. The resistance value R3 is known, and by measuring the voltage v1, 1=Vi/R3
Therefore, the current to be measured i has been measured. In this specification, the voltage signal ν1 obtained by converting the current i in this manner is referred to as the current to be measured i.

The square calculator 6 inputs the output an of the ADC 2, and outputs a value b(n) obtained by squaring the output an.

b(n)=Bn-Bn=Bn That is, the square value calculator 6 outputs the square value of the instantaneous value an at the sampling number t=n. Square calculator 6
The output is a digital value, and the solid line waveform in FIG. 2 (2) is an analog representation of this. Figure 2 (
The solid line waveform of 2) is the sampling value Bl, B2. B
3. Since it is the square value of ..., Bn, ..., it has a step-like shape. Note that the dotted line waveform in Figure 2 (2) is similar to Figure 2 (1).
) is the ideal square waveform of the waveform.

The exponential averaging calculator 7 exponentially averages the data b(0) output from the square calculator 6, and its output P
If (n) is expressed in an analog way, it becomes (3) in Fig. 2. Add explanation. The exponential averaging calculator 7 includes, for example, a calculation section 71 and a memory 72.

The calculation unit 71 repeats the calculation of equation (2) every time data b(n) is added from the square calculation unit 6. That is, the calculation unit 71 receives the square value b(n
), the previous calculation result P(n-1) is introduced from the memory 72, the calculation of equation (2) is performed, and the output P(n) is stored in the memory 72 and added to the square root calculation unit 8.

P(n)-P(n-1)+(1/G) ・(b(n)
-P(n-1)) (2)Pin): Number of samplings t = Indexed average result processed up to the beginning P(n-1): Number of samplings t = 1n-1)
Exponential average result b(n) processed up to this point: Square value of the instantaneous value of the signal under measurement at the number of sampling times t=n 1/G: Exponentialization constant (1/G ((1) Here,
Since 1/G < (1), if the calculation of equation (2) is repeated every time b(n) is added to the exponential averaging calculator 7, the waveform shown in FIG. 2 (3) will be obtained. That is, Equation (2) means that if this calculation is repeated, P(n) becomes the average value of the waveform of b(n). Therefore, the final value in Figure 2 (3) is the average value of bfn). matches the value.

In other words, from the exponential averaging calculator 7, b(n) = an
In addition, Fig. 2 (3) can be calculated using only a small number of calculations (Pfn)
The value of is drawn to be constant, but in reality, for example,
By repeating the calculation number of times n = 1000, P(n)
The value of becomes constant.

Outputs the effective value of signal B.

A square calculator 6 with such functions and an exponential average calculator 7
The square root calculator 8 can be configured using, for example, a digital signal processor (hereinafter referred to as DSP) 5.

The central processing unit (hereinafter referred to as CPU) 9 displays.

Note that the number of calculations matches the number of tallock signals, so in FIG. 1, a frequency divider 11 is used, and when a predetermined number of tallocks occurs, a signal is added to the CPU 9 to notify that the predetermined number of calculations have been performed. ing.

Assume that in the apparatus shown in FIG. 1 as described above, a signal to be measured (which may be a voltage signal or a current signal) having a waveform shown in FIG. 2 (1), for example, is applied to the terminal P1 starting from time TS. Here, since the tally signal SC with period TAD is applied from the tally generator 3 to the S/8 circuit 1, the second
The sample data indicated by the black circles shown in Figure (1) is imported. Then, this data is successively converted into digital values by the ADC 2.

Note that the delay line 4 slightly delays the timing of the clock signal SC applied to the S/8 circuit 1, so that the ADC 2 can take in a value with a stable hold state.

The square calculator 6 calculates the square value b of the instantaneous value Bn of the signal under measurement B.
Output fn)=an. If this b(n) is represented in analog form, it becomes a solid line waveform shown in FIG. 2 (2).

When the calculation of the above equation (2) is added to the data bin marked with a black circle in FIG. 2 (2) by the exponential averaging calculator 7, P
The trajectory of the value of (n) has a waveform as shown in FIG. 2 (3). The finally settled value of P(nl) obtained in this way is (effective value of the signal under measurement) 2.

When the square root calculator 8 repeats this calculation a predetermined number of times (for example, nA) such that the effective gl of the signal under test 2 and Pin shown in FIG. The signal is applied to the CPU 9, the CPU 9 reads the output of the square root calculator 8 at that time, and based on that value,
The effective value is displayed on the display 10.

In the above description, it has been explained that the square root calculator 8 always performs a square root calculation on the output signal of the calculation unit 71, but the frequency divider 1
The square root calculation may be performed only when a signal of 1 is applied to the CPt19.

In the apparatus shown in FIG. 1, two display methods shown in FIGS. 3 and 4 are possible.

The display method in Fig. 3 is to update the display value to display the output of the square root calculator 8 based on the point (△ mark) where the indexed average output P(n) becomes the final value or near the final value), and then the display value is updated to display the output of the square root calculator 8. 7
Clear the contents of 2 and set Pfni) to O), then set it to 0 again.
This is a method to start calculation from .

The display method shown in FIG. 4 does not clear the data in the memory 72, but displays the indexed average output P(n) for each fixed number of calculations.
This is a method of displaying the output of the square root calculator 8 based on .

Effects of the Present Invention> As described above, according to the present invention, the following effects can be obtained.

(1) Since measurement can be performed regardless of whether the period of the signal under test waveform is an integral multiple of the sampling period, a circuit for measuring the period of the signal under test waveform is not required. Also, there is no need for means for controlling the sampling period to be an integer fraction of the period of the input waveform. Therefore, costs can be reduced.

(2) Since calculations are not performed until an integral multiple of the half period of the input waveform matches an integral multiple of the sampling period TAD, the measurement response time does not become long.

(3) Also, since there is no need to shorten the sampling period,
There is no need to use expensive ADCs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a configuration example of an effective value measuring device according to the present invention, FIG. 2 is a diagram showing signal waveforms of each part of the device in FIG. 1, and FIG.
Figure 4 shows the timing of measurement data and display.
FIG. 5 is a diagram illustrating a conventional example. DESCRIPTION OF SYMBOLS 1... S/8 circuit, 2... ADC, 3... Tarock generator, 6... Square calculator, 7... Exponential average calculator, 8... Square root calculator, 9...CPu. ζ7,

Claims (1)

[Claims] AD conversion means (1, 2) that samples an analog signal under test at a certain period and converts the sampled value into a digital signal, and performs a squaring operation on the digital output signal of the AD conversion means. A squaring calculator (6) that inputs the squared data and performs an exponential averaging operation thereon; , a square root calculator (8) that performs a square root calculation of these, and an effective value measuring device.