EmonPI not honoring voltage calibration after switch to emonPI_CM firmware

Hardware emonPi
1

I am using an original Emon PI 1 with an AC-AC adapter in Mexico.

After upgrading to the continuous sampling firmware 1.1.4, the Vrms readings are almost the double of the actual values.

The interfacers configuration is set to 110V, but it seems not to be honoring it:

    [[RFM2Pi]]
        Type = EmonHubJeeInterfacer
        [[[init_settings]]]
            com_port = /dev/ttyAMA0
            com_baud = 115200
        [[[runtimesettings]]]
            pubchannels = ToEmonCMS,

            group = 210
            frequency = 433
            baseid = 5
            calibration = 110V

I changed the scales values in the nodes configuration from 0.01 to 0.005 to mitigate but I don’t think this the solution.

Using the Serial Monitor I sent the L command and I got this:

|vCal: 268.97

This suggests the firmware it’s not reading the configuration file (not sure how it’s done).

Is any fix available? Perhaps I should re-compile the firmware with a correct setting for vCal?
My guess is that would be:

vCal = (127V x 13) / 11.6V = 142.32

(The nominal voltage in Mexico is 127V)

2

I decided to recompile the firmware after changing the following lines:

float vCal  = 268.97;
float lineFreq = 50;

Now I’m getting Vrms = 132.56 (whereas the reading with a multimeter is 129.7V).

1 Like
3

You can also configure it over the serial link. If you send k0 142.32 (where 142.32 is the calibration value), that will set it. Follow that by s to save to EEPROM.

1 Like
4

Sadly and confusingly, that is not a calibration value, it is a logical flag, it must be either 110 or 230, that sets one of two fixed numbers - one for 120 V (North American standard) or the one for 230 V (European standard).

If you look on the Admin page of emonCMS, you will find the Serial Config tool. You can use this to change (and save in EEPROM) the voltage calibration for the ‘emon’ part of your emonPi. You then do not need to change the “scales=…” values.

The configuration is documented here:

The number you need for vCal depends on the actual voltage under no load of your a.c. adapter at your nominal 127 V. It is the supply voltage that would give you 13.0 V out of your a.c. adapter. (This is theory - you do not need, and will not usually have, 13 V from the a.c. adapter.)

If you have two voltmeters, you can measure the input and output voltages of your adapter to obtain the voltage ratio, or if you have only one, measure the voltage on your supply and adjust the calibration so that you read the same value on the emonPi.