# Setting up a P1 (CT100) feed

I am new to this. I am using a wifi enabled TX3 and emoncms.org. I have search the manuals, forums and spent a lot of time experimenting.

How do I setup my input so that I can get two feeds from it. My attempt below does not work.
i) instantaneous power (in watts)
ii) daily accumulation on energy (in kwh)

Many thanks, George

Hello George, to record power and cumulative kWh you only need two processes, Log to feed and Power to kWh, you can remove the others.

Thanks. I am slightly confused now. There is an E1 and a P1 input in my emontx3. Which should I be using?

Should I just use the P1 for the instantaneous power in Watt, and the E1 for the cummulative energy consumption in Wh?

I can then esily convert to kW and kW in the report output.

The difference between power converted to energy in emonCMS and energy directly reported by the emonTx is this: if the data fails to make it to emonCMS, the accumulated energy from the emonTx will be accurate; whereas the change in the accumulated energy in emonCMS will be calculated (estimated) from the two powers either side of the break.

So you can use whichever method you prefer.

Thanks, the best way to get the energy is from the E1 input. So… E1 = kWh; P=1 Watt. I have the P1 feed setup. I am not getting the correct power appearing.

I now want to configure the E1 input to give me two feeds. I would like two accumulated feeds in Wh and kWh. I have set up as below, but the kWh is not correct. It seems to be a factor out. What could be wrong?

Why are you trying to convert Wh to kWh by using Power to kWh? E1 is already in units of energy - that’s why it is called “E1” - E for energy.

In short, what’s wrong is your maths.

If you want to convert watts to kilowatts, you multiply by 0.001. The same for Wh to kWh.

Why am I trying to do this? Because the way that the E1 is presented is confusing. If it was called E1 (Wh) then it would be more obvious. Equally, the function ‘Power to kWh’ would be better named (W to kWh).

So, as the E1 is already supplied in Wh. All I need to do is multiply it by 0.001. Easy. When you know.

Thank you very much. Hopefully this thread will help others. George

Erm… You’re the one who wrote that, so I thought you realised that E was for Energy and P was for Power.

I suspect they’ve been abbreviated to just En & Pn to save bytes when sending the data in JSON format.

Or “Power to Energy” or possibly “Integrate Power over time” because it can be used with other units where integration over time is required.

And for completeness, this is how I configured the energy input, which provides the Wh and kWh values.

If the power feed being measured (eg P1) can be both positive and negative (for example when measuring grid usage with solar pv generation), then presumably the energy E1 would show the net power (i.e. import - export power)?

Welcome, Duncan, to the OEM forum.

Which it can indeed be (provided that you have measurement of both current and voltage)

Not only would, but it does.

(Note that there was an error in the sketch that has only recently been corrected, where the signed value of energy was assigned to an unsigned variable for transmission - resulting in very large positive numbers if the nett energy flow was negative - export in our convention.)

Thanks Robert. Yes Indeed I can see the very large Energy value from a CT clamp which my electrician installed in my consumer unit to measure an ashp. The clamp is obviously the wrong way round. I have simply multiplied the negative power it is showing to correct that, but I am unsure how to correct the E value. I saw a discussion on this forum about it but wasn’t sure how to implement the fix as I am new to all this.
Could you explain in simple terms how I can fix this E value please?

What equipment are we talking about here - an emonTx V3.4 passing the data by radio to an emonPi, emonBase, emoncms.org?

I have a emonTx V3 (bought in June 2020) passing data by radio to an emonBase.

OK, in your emonBase, I think the emonTx is NodeID 15.

On the inputs page for that, you need to add these process steps into the processing of the energy value.

× [Value: -1]
If >, skip next [Value: 2147483647]
log to feed [whichever it is]
+ [Value: 4294967294]
log to feed [whichever it is - the same one]

Click on the spanner icon against the energy input, and above the blue panel is a row of boxes, some with drop-downs. Starting at the left, select “×”, type the number “-1” in the next box and click “Add”. Continue adding the other steps in the processing - the last one obviously adds to the feed you used in the second step, don’t create a new one.

You can correct saved values, but if you don’t have much data and you’re not bothered about losing it, the best is probably to empty the feed of data - or delete the feed and re-create it. You delete the feed or empty it on the Feeds page.