Most of the time whenever I come across electricity metering or CTs, there is always a term like an accuracy class e.g. 0.2, 0.5, 1, 2, etc. I have an idea about what this accuracy class means.

But alongside this info, there is something like "accuracy of 0.2 in the range of 1000:1". What does this "in the range of 1000:1" represents.

For example, there is a Metering IC named HLW8012, https://tinkerman.cat/post/hlw8012-ic-new-sonoff-pow

I couldn't find its datasheet in English, however, I translated the document, and the following info was deduced:

  • High-frequency pulse CF, indicating active power, meeting the accuracy requirements of the 50/60Hz IEC 687/1036 standard, in the 1000:1 range Accuracy of ±0.2% is achieved within the range.

  • High-frequency pulse CF1 can be configured as the effective value of the output current or the effective value of the voltage, reaching ±0.5% in the range of 500:1 Accuracy.**

What does it mean by:

  • "in the 1000:1 range" accuracy of ±0.2% ?
  • "in the range of 500:1" accuracy of ±0.5% ?
  • \$\begingroup\$ Does it refer to current transformer by any chance? They commonly come in 1:1000 ratio. \$\endgroup\$
    – winny
    Commented Nov 30, 2021 at 11:12
  • \$\begingroup\$ The accuracy class is probably bound to some standards that may be related to the country you are in (It might be the uncertainty level of confidence sigma but it is usually represented as k=xxx), as for the range, it needs more context (photo?) \$\endgroup\$
    – Damien
    Commented Nov 30, 2021 at 11:26

1 Answer 1


It just indicates the accurate reading range as a "ratio" of the meter's rated current.

Assuming you have a single phase, 180-264V, 100A electronic electricity meter. If it says "current reading accuracy of 0.2% in a range of 1000:1" then it means that it can measure the phase current range of 0.1A (100A/1000) to 100A (100A/1) with an error of 0.2%. Or in other words, it can measure the phase currents down to one thousandth of the rated current (100A/1000 = 0.1A) with an error of 0.2% (i.e. 99.8% accuracy).

As you might guess, the accuracy will drop as the ratio increases. For example, the error can be 2% for 5000:1.


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