JPH06294828A - Power measuring apparatus - Google Patents

Abstract

PURPOSE:To measure power of a wide band up to a very low frequency by conducting an exponential mean calculation at an input in the case of a normal frequency and conducting a total sum average calculation in the case of a low frequency. CONSTITUTION:A comparison judging unit 13 compares a frequency fin of input V, I to be measured with a preset value fo, guides an output of an exponential average calculator 82 to a microprocessor 9 at the time of fin >=fo, interrupts a DSP 8 in the case of fin <=fo, finishes a calculation of the calculator 82, then clears its value, the processor 9 fetches an output of a total sum mean calculator 84 based on the judgement of the unit 13, and displays its value on a display unit 10. Thus, if a frequency of an AC input to be measured is a predetermined value or more, an exponential mean calculation is conducted, while if it is the predetermined value or less, a total sum average calculation of one period (or several periods) is conducted. Accordingly, even in the case of a very low frequency, power value of the input to be measured can be measured without increasing a measuring time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power measuring device for measuring active power of an AC signal by using an exponential averaging method.

[0002]

2. Description of the Related Art An example of a conventional power measuring device using the indexed average method will be described with reference to FIG. In the figure, P1,
P2 is a terminal to which an AC voltage V and a current I are input, 1 and 2 are sample and hold circuits, 3 and 4 are analog-to-digital converters (hereinafter referred to as ADCs),
Reference numerals 5 and 6 are delay lines, and 7 is a clock generator. The clock obtained from the clock generator 7 is the sampling signal SC.
Is applied to the sample and hold circuits 1 and 2 as well as to the ADCs 3 and 4 via the delay lines 5 and 6.

8 is a digital signal processor,
It is composed of a multiplier 81, an arithmetic unit 82 for executing the exponential averaging by calculation, and a memory 83. If the output of the ADC 3 is V (t) and the output of the ADC 4 is I (t), then V
Each of (t) and I (t) is guided to a multiplier 81 included in the digital signal processor 8 for multiplication, and the multiplier 81 outputs a signal of m (t). m represents an instantaneous value of electric power, and t represents the number of times of sampling. This instantaneous power m (t) signal is given to the indexed average calculator 82. The calculator 82 exponentially averages the m (t) signal. Each time the data m (t) is added from the multiplier 81, the following equation (1)
Repeat the operation of.

That is, the arithmetic unit 82 obtains the instantaneous power value m (t) from the multiplier 81 and the previous arithmetic result a from the memory 83.
(T-1) is introduced, the operation of the equation (1) is performed, and the output a (t) is stored in the memory 83. a (t) = a (t-1) + (1 / G) {m (t) -a (t-1)} (1) In the formula (1), a (t): by the sampling number t Processed indexed average result a (t-1): Processed indexed average result up to the sampling number (t-1) m (t): Instantaneous value of electric power at sampling number t (1 / G): Index (1 / G << 1) Here, since 1 / G << 1, the equation (1) is repeatedly executed every time m (t) is added to the exponential average calculator 82. As a result, the signal a (t) extracted from the output terminal of the arithmetic unit 82 is converted into an exponentially averaged value of the instantaneous power m (t), that is, active power which is a product of the input AC voltage V and the current I. It becomes the corresponding signal.

Reference numeral 9 is a microprocessor, and 10 is a display. The output of the digital signal processor 8, that is, the output signal a (t) of the exponential averaging unit 82 is taken in by the microprocessor 9, and its value, that is, the active power value is displayed on the display 10 controlled by this microprocessor. Is displayed. A frequency divider 11 divides the output of the clock oscillator 3, and this frequency-divided output is given to the microprocessor 9 as a clock. A power measuring device using such an indexed average method has been developed by the applicant of the present application and has already been filed as Japanese Patent Application No. 2-227112.

By the way, in the device of FIG. 3, in order to improve the responsiveness of the exponential averaging operation, the value of "G" in the arithmetic expression expressed by the equation (1) is reduced. Just do it. However, when the value of “G” is reduced, ripples are included in the output when the input AC signals V and I have low frequencies, and the measured value fluctuates. It is necessary to increase the value of "G" to eliminate the fluctuation of the measured value,
Then, there is a problem that the response becomes slow and the measurement takes a long time.

[0007]

An object of the present invention is to improve such a point, and in an apparatus for measuring AC power using an exponential averaging method,
An object of the present invention is to provide a wide band power measuring device capable of measuring power up to an extremely low frequency without extending the measuring time.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to an analog / digital converter for converting an input AC voltage and a current into digital signals, a multiplier for multiplying the outputs of both analog / digital converters, and the input. A frequency fin of AC voltage or current is compared with a preset frequency fo, and when fin ≧ fo, an exponential averaging operation is performed on the output of the multiplier to give it to the microprocessor; In the case of ≦ fo, a digital signal processor including a sum and average calculator that performs sum and average calculation on the output of the multiplier and gives it to the microprocessor is provided, and the output value of this digital signal processor is The display is controlled by the processor.

[0009]

In the present invention, the input is subjected to the exponential averaging operation at a normal frequency, and the input is subjected to the sum averaging operation at a low frequency.

[0010]

The present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram showing an embodiment of the device of the present invention, and FIG. 2 is a flow for explaining the operation thereof. In the apparatus of FIG. 1, the same parts as those of FIG. 3 are denoted by the same reference numerals as those of FIG. 3, and their re-explanation is omitted. In FIG. 1, reference numeral 12 is a frequency measuring device for measuring the frequencies of the AC inputs V and I to be measured, the input end of which is connected to the input terminals P1 and P2. Reference numeral 13 is a comparison / judgment device for comparing / judging the frequency fin of the measured AC inputs V and I detected by the frequency measuring device 12 and a preset value fo. Reference numeral 84 is a sum-and-average calculator, the input end of which is connected to the output end of the multiplier 81 constituting the digital signal processor 8 and which represents one cycle (or number) of the output of the multiplier 81 represented by m (t). The average value of the sum total of (cycle) is calculated. The output of the sum average calculator 84 is applied to the microprocessor 9. The output of the indexed average calculator 82 is also added to the microprocessor 9. The comparison / judgment unit 13 judges whether the signal applied to the microprocessor 9 is the sum average calculator 84 or the output of the indexed average calculator 82.

That is, normally, the comparison / judgment unit 13 compares the frequency fin of the measured inputs V and I with the preset value fo, and when fin ≧ fo, the output of the exponential average calculator 82 to the microprocessor 9. Then, the power value is obtained by executing the indexed average calculation. On the other hand, the frequency measuring device 12 measures the frequency fin of the measured input in parallel with this calculation.
As a result of the frequency measurement by the frequency measuring device 12, fin ≦ fo
, The comparator / determiner 13 interrupts the digital signal processor 8. When an interrupt signal is input to the digital signal processor 8, the exponential averaging operation unit 82 terminates the exponential averaging operation up to n samples in progress, then clears the value and compares / determines. Based on the judgment of the device 13, the microprocessor 9 fetches the output of the sum average calculator 84, and the value is displayed on the display 10 via the microprocessor 9.

As described above, in the present invention, when the frequency of the alternating current input to be measured is equal to or higher than the predetermined value, the exponential averaging operation is performed, and when the frequency is equal to or lower than the predetermined value, the sum average of one cycle (or several cycles) is calculated. Since the calculation is performed, the power value of the input to be measured can be measured without extending the measurement time even with an extremely low frequency signal.

[0013]

According to the present invention, in a device for measuring alternating current power using the exponential averaging method, a wide band alternating current which enables measurement of signals up to extremely low frequencies without extending the measurement time. A power measuring device can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a device of the present invention.

FIG. 2 is a flow chart for explaining the operation of the device of the present invention.

FIG. 3 is a circuit configuration diagram of an example of a conventional device.

[Explanation of symbols]

 1, 2 Sample-and-hold circuit 3, 4 Analog-to-digital converter 8 Digital signal processor 81 Multiplier 82 Exponential averaging calculator 83 Memory 84 Sum-averaging calculator 9 Microprocessor 10 Display 12 Frequency measuring instrument

Claims (1)

[Claims] 1. An analog-digital converter for converting an input AC voltage and a current into a digital signal, a multiplier for multiplying outputs of both analog-digital converters, and a frequency fin of the input AC voltage or current. A pre-preset frequency fo is compared, and when fin ≧ fo, the output of the multiplier is subjected to an exponential averaging operation to be given to the microprocessor; and when fin ≦ fo, the multiplication A digital signal processor comprising a sum-and-average calculator for giving a sum-and-average calculation to the output of the detector and giving the output value of the digital-signal processor to a display controlled by the microprocessor. A power measuring device configured to display.