Add Optical Pulse Sensor

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Optical Pulse Sensor

An Optical Pulse Sensor detects the LED / IR ‘pulse’ output from a utility meters. Each pulse corresponds to a certain amount of energy passing through the meter. The amount of energy each pulse corresponds to depends on the meter. By counting these pulses and measuring the time between each pulse the meters KWh value can be calculated.

Unlike clip-on CT based monitoring, pulse counting is measuring exactly what the utility meter is measuring i.e. what you get billed for. Pulse counting cannot provide an instantaneous power reading like clip on CT sensors can. Where possible, we recommend using pulse counting in conjunction with clip on CT sensors.

The emonPi and emonTx can simultaneously perform pulse counting and CT based monitoring.

Due to hardware limitations only a single pulse counting sensor can be connected to a single emonPi, emonTx or emonTH unit.

  1. Identify your utility meter’s pulse output, usually a red flashing LED marked ‘KWh’. Stick the supplied self adhesive base-pad over the LED, carefully aligning the hole in the center of the circle so the flashing LED shines through clearly. Be sure to clean any dust from the meter face before attaching the sensor.

  2. Attach the sensor to the circular base sticker by pressing the sensor head firmly in place. Take care to ensure sensor is centered over the pad.

  3. Plug sensors RJ45 connector into emonPi / emonTx RJ45 socket.

Ensure the sensor is plugged into the RJ45 socket on the emonPi on the same side as the CT connection jack-plug sockets NOT the Etherent socket.

If installed correctly when the emonPi / emonTx is powered up the pulse sensor LED should flash in sync with the utility meter LED. See video clip:

You may need to swich on a large electrical load e.g. kettle to generate some pulses

View the Input list:

Clicking the spanner icon brings up the feed input processor. It’s a good idea to log the raw pulse count to a feed for debugging. The pulse count needs to be multiplied by a scalar to convert the pulses to Wh. The scale factor will depend on your meter, see the table in Appendix A below. Once the scalar has been applied, log the result to a Wh Accumulator feed. This feed is an ever increasing number which won’t return to zero if the emonPi / emonTx is reset, which would result in the raw pulse count returning to zero.

Viewing the Wh accumulator feed:

To convert the wh accumulator feed to daily KWh bargraph using the graph tool select Window type-daily feed type=Bars and delta = 1 then click reload

See Emoncms daily Kwh guide for mor info.

The optical pulse sensor should work with all utility meters that have an LED or IR optical pulse output. The sensor has been tested to work with the following meters. The ‘pulses per kwh’ calibration can be used to configure the input process for the pulse data, see above:

Meter Image Pulses Per KWh

Multiplication factor for

Wh Accumulator feed

Elster A100c

(single phase)

1000 1000 / 1000 = 1

Actaris ace9000

(single phase)

800 1000 / 800 = 1.25

Xil XLA12

(single phase)

800 1000 / 800 = 1.25

Elster A1100


500 1000 / 500 = 2



Elster A1140


1000 1000 / 5000 = 1

Landis & Gyr 5254E

(single phase)

1000 1000 / 1000 = 1

 Inepro PRO1D

2000 1000/2000 = 0.5


AMR Smart Meter

1000 1000 / 1000 = 1

Landis & Gyr E110

(Single Phase)


1000 / 1000 = 1

Please help us expand this table by contributing details for your meter. Email photo and scale factor to [email protected]

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