Which Meter Constant should a Meter have?

Actually this question came up recently from a utility customer. The answer is clear, when we have a higher constant, the testing is faster.
The most time-savings are coming from the no-load test and the starting test.

We have a three-phase meter, Un = 230 V, Ib = 5 A, Imax = 60 A, accuracy class 1.

Testc = 400 i/kWhc=1600 i/kWh
no-load36:14 mm:ss09:04 mm:ss
starting26:06 mm:ss06:32 mm:ss

You see, by simply increasing the meter constant you can save more than 45 minutes testing time and enlarge the laboratory capacity.

Can my test bench handle such fast flashing pulse output?

It seems that this is the major concern for many utilities. The oldest version of the IEC62052-11 from 2003 gives already an allowed maximum frequency for pulse outputs of 2.5 kHz. Since the first generation of computed error calculation all test bench manufacturers have taken care to match the 2.5 kHz for scanning. We did some internal tests and pass even 8 kHz.

What is the frequency of a flashing pulse output when we have a three-phase meter with 230 V and maximum current of 100 A?
You can calculate manually or you use the pulse calculator.
The result is 30.6 Hz :)

If your test equipment has a reference standard and individual error calculation for each position or if it's newer than 2003 it's likely impossible that the equipment can't detect a 31 Hz flashing frequency.

If you are in doubt, talk to us. Please always consider the meter constant as very important factor for the testing time. If you want to replace your old test bench, take a look here.

What is your experience? Share your thoughts with us and leave a comment.
Thank you for reading.

Editor's note: This article was originally published in July 2020 and has been updated for comprehensiveness.

2 Replies to “Which Meter Constant should a Meter have?”
  1. Dear Sir,
    when the test the energy meter with meter constant is 10000 imp/kwhr,i am getting error value . But when i test the energy meter with meter constant is 16.8 kwh/imp,i am not getting proper error value(it's coming HH.HHHH%).
    I am using ZERA kit for taking error value.I need to know the reason.

    1. Actually you need to change the settings when you want to input the constant in Wh/imp. ZERA has also this feature.

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