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Why Does The Smart Meter Display Produce An Indication Error?
- Aug 05, 2018 -

Someone asked, the total power display value of the three-phase electronic multi-function smart energy meter used at a certain time is not equal to the sum of the displayed values of each time period. What is the reason?

The three-phase electronic multi-function smart energy meter is a numerical value for displaying electric energy on the liquid crystal screen. There are 8 effective digits, of which two significant digits after the decimal point. It is reasonable to say that at a certain time, the increment of the total energy measured should be equal to the sum of the energy increments at different times during the statistical period. However, sometimes there is a case where the sum of the energy increments in different periods of time in a certain statistical period is not equal to the value of the total energy increment in the time, that is, 1 to 2 digits appear in the last second decimal place. Indication error.

The cause of the analysis is as follows. Because the total energy increment measured during a certain period of time is continuous from the beginning to the end of the time, the effective value of the two digits until the decimal point should be correct. However, the sum of the increments of the electric energy in the different periods of the peak, the peak, the flat, and the valley in the corresponding time may cause an indication error, because the microprocessor built in the electric energy meter processes the data according to the following principle, that is, the display value of the liquid crystal, Only the second digit after the decimal point is displayed, and the third digit of the decimal and the following mantissa are discarded. (No matter what the third digit is after the decimal point, it will not be displayed or carried.) However, the mantissa after the third and third digits will still be stored in the internal memory, waiting for the next time the power is generated, and the calculation will be performed. . That is to say, the increment after the second decimal place in each period, if this time is not counted, will be counted next time, and there is no loss of data. Only the display error of the last bit will be generated on the LCD display. (What should be emphasized here is not the measurement error, because the mantissa is still stored in memory)

In addition, according to the National Standard GB/T15284-2002 "Special Requirements for Multi-Ratio Electric Energy Meter", the indication error of the electric energy meter is as follows: (Excerpts are as follows)

5.8 Power indication error

5.8.1 Rate indication error during rate period

5.8.2 Counting value combination error

    b) Electronic display (counter)

       ‖△WD—(△WD1+△WD2+ ......+△WDt)‖≤(n-1)×10—β (5)

   In the formula:

     △WD ----- indicates that the electric energy of the total energy counter is electronically displayed during the time;

       △ WD1 + △ WD2+ ...... + △ WDt ---- - indicates the power increment of the counter corresponding to each rate period in the time;

     n--- indicates n rates;

β--- indicates the decimal number of the electronic display total energy counter.

Our multi-function energy meter has four rates for peaks and valleys, and the LCD screen has two decimal places. Substituting into the right formula of equation (5) is:

     ≤(n-1)×10-β

     =(4-1)×10-2

        = 0.03

   According to the national standard GB/T15284-2002, the indication error of the multi-function electric energy meter is less than or equal to 0.03, and not more than 0.03 are in compliance with the national indication value error requirement.


Zhejiang Reallin Electron. Co., Ltd

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