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Power1pluspower2 calibration in Emonhub

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I have calibrated the two CTs that I have connected into power1 and power2 channels and put the calibration values in the Emonhub. I have been using the power1pluspower2 input to calculate the house load and then used that in the MySolar app. Can anyone tell me if I need to calibrate the power1pluspower2 input in emonhub as well or does it take the values needed for each CT from the respective Emonhub power1 and power2 inputs ?

Sorry if this is already written up somewhere but I couldnt find it.

Unfortunately, you cannot calibrate ‘power1pluspower2’ accurately. It is derived in the front end Atmel '328P sketch before the data reaches emonHub. Any calibration you apply in emonHub will therefore be a compromise, because it won’t know the proportion to allocate to the two parts.

I suppose, if you’re really keen, you could apply the calibration inside emonCMS - on the inputs page, by adding a tiny fraction of power1 and a different fraction of power2 to the sum. It should work.

The reason for sending the sum value was because the two inputs could end up separated by 5 s due to timing differences. If you add the correction in emonCMS, that could apply to the correction, but it’s a second-order effect, so it might not worry you.

Don’t worry, I doubt very much that it’s written anywhere.

Thanks Robert. I think I’ll just use the two separate inputs and ignore power1pluspower2. I’m not sure I’m going to be particularly bothered by a few seconds difference between the two values.

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