EmonTx - a question about accuracy at low power

[borpin (Brian Orpin)]

@johnbanks

How do you do that?

I did quite a bit here about how I connected serially. Final bit was re uploading a new sketch to the TX. Does assume the tx line and rst is connected.

EmonTX to Rpi - Direct Serial Connection

Took my life in my hands and Success!! . Having installed the system using the emonScripts, some of the elements were already in place. First compile the sketch. I know that @Robert.Wall is not keen on PlatformIO, but on the Pi it installed and worked flawlessly as described here GitHub - openenergymonitor/EmonTxV3CM: EmonTxV3 Continuous Monitoring Firmware (Default shipped EmonTxV3 firmware). The only oddity is creating the hex file. That instruction says use the upload option but t…

[Robert.Wall]

For completely different reasons, I’ve measured the current linearity of emonLibCM in an emonPi. It uses the same components as the emonTx. At 0 A, it read 140–150 mA. At 0.501 A, it read 0.54 A. At currents of 1 A up to 100 A, the error was 0.3% or less, which is well within the accuracy band of the multimeter that I was using.

Note: Transformer phase errors that naturally increase at very low currents mean that this result cannot transfer to the real power that is calculated from the voltage and current readings.