KR840001160B1 - Digital type watt-hour meter - Google Patents

Abstract

A digital watt-hour meter consists of a voltage divider, a current/voltage converter, an A/D converter, a microprocessor, and a ROM that stores the program. The A/D converter starts converting input analog values to digital values with start signal from the microprocessor. The converter indentifies the final conversion with a status signal and sends the signal to the microprocessor. The conversion speed is determined by the sampling time (ΔT), and the used power is calculated by a successive approximation, method in the microprocessor. By setting the flag of a timer, the amount of graded watt-hours can be calculated.

Description

Digital integrated power meter

1 is a basic principle diagram of the present invention.

2 is a schematic diagram of the present invention.

3 is an input circuit diagram (voltage divider circuit and current voltage conversion circuit) of the present invention.

4 is a microprocessor block diagram used in the present invention.

5 is a program flow chart of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital watt hour meter for measuring the amount of power used by time-dividing and integrating a voltage current using a microprocessor.

Currently, the integrated wattmeter is a Ferraris-type integrated wattmeter using Arago discs.The driving part has a mechanical structure, so the wear is severe and errors accumulate, resulting in low reliability and short mechanical life. It must be calibrated periodically, and accurate power billing is difficult due to the low precision of the mechanical structure. In the case of large customers, accurate power calculation is required, but high precision (more than 0.5 class) instrument with mechanical structure is very expensive.

In addition, when the differential power calculation is required, a mechanical integrated power meter has various inconveniences such as attaching a separate device or attaching an expensive instrument where the differential power is calculated mechanically.

The present invention is to compensate for the above-mentioned shortcomings, and is a digital integrated power meter having high reliability, precision, and semi-permanent lifetime by using a semiconductor device, and the operation principle of the digital integrated power meter of the present invention is as follows.

The measuring procedure takes the voltage and current of the power line, multiplies the instantaneous value, accumulates it, and displays the required amount on the indicator. In other words, the amount of power is obtained by time-integrating and integrating voltage and current.

The counting integrated power meter of the present invention is to I / C the circuit configuration and to control the electric system by a program using a microprocessor, so that even if the same hardware (Hardware) according to the user's purpose in software (Software) It has various additional functions.

FIG. 1 shows the basic theory of the coefficient integrated energy meter of the time division integration integral of the present invention. As shown in this figure, the amount of power used is measured by multiplying and integrating the instantaneous value of the voltage waveform and the current waveform i.

In Figure 1, the voltage waveform e, the current waveform i, the half cycle T, the maximum voltage Vm, the maximum current Im, the frequency f, the voltage-current phase difference α

Voltage, current active power, etc. are expressed as in Equations (1)-(4).

Therefore, the effective amount of power to be obtained is as follows.

According to equation (5), the effective power amount is obtained by multiplying the instantaneous values of voltage and current regardless of the phase difference of voltage and current, that is, the power factor, and accumulating according to the encoding time of the product of voltage and current.

The schematic diagram of the digital integrated power meter of the present invention is shown in FIG.

Referring to the schematic diagram of FIG. 2, the voltage divider circuit stepped down the voltage waveform by K times using the resistance distribution method, and the current-voltage converter circuit converted the current waveform by twice the voltage source using the resistance distribution method using CT. .

The voltage divider circuit and the voltage-conversion circuit are shown in FIG. In FIG. 3, Ci is a capacitor for compensating the phase difference between the current and the converted voltage caused by the inductance of the secondary coil of C.T.

In the schematic diagram of FIG. 2, the analog-digital converter is a converter using a successive apprexmation method, and the analog value inputted as an input is converted into a digital value by a conversion start signal of the microprocessor. When the conversion is complete, the status signal is a status signal that tells the microprocessor that the conversion is complete.

The microprocessor examines this status signal and reads the converted data when the conversion is complete. The conversion speed of the A / D converter is selected by the sampling time of the system.

In the schematic diagram of FIG. 2, the system after the analog-to-coefficient converter except the indicator is made by a microprocessor. The structure of the microprocessor is shown in FIG. In FIG. 4, the ROM (Read Only Memory) contains a program that manages the entire system of the digital integrated power meter of the present invention. The program flow chart of the digital integrated power meter of the present invention is shown in FIG.

Accumulated power is a function of time t expressed by instantaneous power × Δt × (Δt: sampling period) according to Equation 5, so the sampling period Δt is important because the sum of instantaneous power × Δt is added over time. It will be one of the elements.

Therefore, the present inventors determine the optimum sampling period in consideration of the voltage division coefficient K, the current-voltage conversion coefficient K ', the sampling period t, the similar-coefficient conversion speed, the clock cycle of the microprocessor, and the like to manage the entire system accordingly. You have completed the program.

Referring to the flowchart of FIG. 5, for the similarity-coefficient conversion, the converter is first given a conversion start signal to cause the converter to start the conversion, then the initial condition of the microprocessor is programmed, and then a timer is displayed for the differential power. Sets or resets a flag from.

Then, when the coefficient-to-coefficient converter completes the conversion, it reads the voltage and current data from the converter, sends a convert start signal to the converter, and multiplies in a program routine that multiplies the two coefficients. At the same time, it checks the sign of the product to determine whether it is positive or negative, adds or subtracts the multiplication result to the cumulative value according to the flag, and the cumulative value is the point value (N). When is reached, the displayed value is increased by that amount, and the displayed value is sent to the indicator for display.

And keep repeating.

In FIG. 4, the interrupt / stop button indicates the amount of power up to that point by pressing this button when measuring the amount of power up to a certain start, and has no relation to the amount of power thereafter.

When the reset / start button is pressed, the microprocessor starts executing from the beginning of the program.

Of course, the interrupt / stop button or reset / start button is not required for a real power line because it is applied only to a test. Accumulation and reading are done in random access memory (RAM), the memory of the microprocessor.

In FIG. 4, the input / output line (I / Oline) is for receiving the output of the similarity-coefficient converter and for giving data to the indicator. The timer is designed to flag the hardware to display differential power so that the microprocessor can distinguish time zones.

As described above, the digital counting meter of the present invention not only compensates for various disadvantages of the mechanical counting meter up to now, but also calculates a differential amount of power, and has an innovative variety of functions that can be easily applied to an automatic inspection system for distribution lines. .

Claims (2)

Analogue value is converted into digital value by A / DConverter which has voltage divider circuit and current-voltage conversion circuit at the input stage and is controlled by microprocessor. A digital integrated power meter that calculates the effective power amount by time division integration by a program of a microprocessor and is displayed on the display. The countable integrated power meter according to claim 1, wherein a differential power amount is displayed by a program by specifying a flag by a timer in a microprocessor.

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