How to get the CM180i Total Power to align with my electrical meter

[mnsandler]

To increase the accuracy of the readings I get from the plugin, i'm trying to calibrate the CM180i total power to my meter. I understand Total power for the CM180i is based on 230V. I'm using the CM180 in the US on a 120V system.

I initially started with a Divisor of 230/120 to adjust the Total Power. However, the plugin Total Power (kWh) continued to climb faster than the meter.

so I adjusted the Divisor to 230/122, but the plugin Total Power is still increasing faster than the meter.

is there a better way to figure out how to get the plugin to align with my meter readings?

[mnsandler]

through trial and error, i'm getting close. i'm now using a divisor of 230/122.34

[mnsandler]

Well that didn't last.

I can't seem to find a divisor that will keep the plugin numbers close to what the meter is reading. the two numbers seem to drift away for each other after several hours.

[b_weijenberg]

The problem with the OWL devices is that they only measure the current flow. The power line voltage is not measured so that the Watts are fluctuating with a fluctuating power line voltage.

An OWL device can therefore not be used to measure an accurate power usage.

[mnsandler]

I have been working on this for several weeks and I think I have found the issue affecting my readings.

the CM180i seem to be reading high across the board. I have added a Divide By value of 1.125 to all 4 of my sensors. This brings down the total amp readings and now I can track kWh that better align with my meter.

ps. I'm in the US on a standard 240V 2-phase residential electrical system.

[mnsandler]

Bert,
I'm not sure if the calculations in the plugin virtual devices (Today Power Usage) are adhering to the divide by values in the cm180i sensor devices.

I setup my own devices and scripts to multiple the total amps by a voltage. the numbers are lower than the plugin calculations.

[b_weijenberg]

The calculation on the physical sensor is (chapter 6.4 in the RFXCOM HS3 User Guide):
Calibration value:
This value is added to the sensor value or subtracted if a minus sign is entered before the value.
Calibration value = (sensor value * Divide By) - Sensor value

Divide by:
The total value (sensor value + the calibration value) is divided by the number entered in this field.


The Virtual sensors use the Device value stored on the physical sensor device.

[mnsandler]

Bert,
the formula for the 'calibration value' doesn't make sense. I thought you previous mentioned that the calibration value was just a +/- offset to the sensor value

so the end result calculated value would be the following

final sensor value = (sensor value + calibration value) / divide by value

[b_weijenberg]

Mark, you are right.