I have a new system, EmonTx + RFM69Pi, arrived from the OEM shop yesterday. Seems to work nicely on a spare Rpi-3B with newly downloaded emonSD image (the EmonTx has AC V monitor, one CT on the mains supply, and an optical pulse counter on my SMETS2 meter).
After warming up by reviewing historic smart meter data I’d uploaded to Emoncms, I tried comparing pulse counting results with fresh smart meter data. I am puzzled to find a few % extra pulses are counted.
For example in 10.5 hours last night, 2.419 kWh were registered by the meter, but 2484 LED pulses were counted. The numbers look random - taking the smart meter data half-hour by half-hour, a scatter plot looks like:
I also correlated actual times (UTC + 1hr) of pulses that I observed (over a 9 minute period) with the pulse counts logged by Emoncms. Sure enough, 36 pulses were counted when I saw only 33 pulses (I can confirm that the sensor green LED pulses when/if and only if the meter red LED pulses, and that the extra 3 pulses came +2 in one 10 s interval and +1 in another 10 s interval. In all other intervals the pulses were counted correctly.
I’ve read at Learn | OpenEnergyMonitor that
This is all happening in a dim basement, so I doubt that ambient light is a problem, but the “logic high output without the green LED lighting” comment suggests to me that the sensor is prone to counting extra pulses that aren’t there.
I’ve also read elsewhere that electrical interference can be mitigated by adding a capacitor here or changing a resistor there. (I think I understand the basics of filtering/smoothing, but electronics isn’t my thing - I’m a theorist by training. I don’t have an oscilloscope but can handle a multimeter and do very simple soldering.)
The last clue I can offer is that the +2 extra pulses happened right when (the compressor in) one of our fridges came on:
but nothing obvious happened (in our house at least) to cause the +1 extra pulse. (I chose the range of this plot to match the period over which I was watching and timing LED pulses.)
Is there anything else I can do towards diagnosing the cause, or should I just psych myself up to do the capacitor/resistor mod?
Thanks in advance for any feedback offered.
Otherwise, may I say what an amazing and delightfully collaborative project this OEM is, even if I am a little daunted by the task of finding my way around the facilities Emoncms has, not least for data analysis.