Flashing LED and optical sensors on energy meters

When installing an optical sensor counting the flashing LED, it is important to know the weight of the flash (pulse) to count the right amount of kWh.

It depends on the current transformer ratio (CT or CTR) and the pulse per kWh of the energy meter


In short, the current of the network (Cn) might be to high for the energy meter to operate normally. Usually, a current transformer is placed to convert Cn to the current expected by the energy meter (Cm).
The ratio is simply
CT = Cn/Cm (e.g Cn = 100A, Cm = 5A, CT = 20)

There are several ways to determine CT:

  • It is configured inside the energy meter (usually going inside the menu of the energy meter)
  • It is written on the front panel of the energy meter

Pulse per kWh

It is also availabe in a parameter of the energy meter or it is written on the front panel


Once both are identified , the weight of the flashing LED can be determined using the following formula:

Weight of the flashing LED = Pulse/CT/kWh

Example of energy meter

Brand: Mega Power Automation Limited

  • Pulse per kWh = 5000
  • CT= 20
    Results is 250 pulses per kWh instead of 5000 if the ratio (CT) is 1:1

Optical sensor
Model Readwatt
The optical pulse sensor is configured to count 1 kWh every 250 pulses (flashing LED)

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