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Need calibration for 220V main , for current and voltage meter


(darrence avon) #1

emon1.voltage(voltagePin, 224.07, 1.7); is this correct for 220V ?


Energy monitoring for 220VAC main
(darrence avon) #2

[Duplicate question merged from a second thread]

emon1.voltage(voltagePin, 224.07, 1.7);
emon1.current(currentPin, 111.1);

is the calibration for voltage correct?


(Robert Wall) #3

The voltage calibration depends on the transformer/a.c. adapter that you use, the components inside whatever device you are using and the tolerance of those and other things. It does not depend on the system voltage. So nobody can say whether a particular calibration constant is correct without knowing the details of your installation.

You can read how the constant is derived in “Learn”.

The only way to be certain of having the correct constant is to measure the supply voltage with a known good meter that is in calibration, and adjust the calibration constant so that emon1.Vrms reads the same value. A similar argument applies to current too.


(darrence avon) #4

ok , thanks a lot :slight_smile:


(darrence avon) #5

and why is it my power factor reading is negative , ?


(Robert Wall) #6

Probably because real power is negative.

Maybe, if you told us a bit more about what you’re doing instead of assuming that we can guess what you have and what you are trying to do, we could give you better and fuller answers.


(darrence avon) #7

oh my bad, im doing an arduino energy monitor , https://learn.openenergymonitor.org/electricity-monitoring/ctac/how-to-build-an-arduino-energy-monitor,, voltage & current reading is ok, but power factor gives negative reading

211V 0.14A PF: -0.45


(Robert Wall) #8

If you’re using the sketch from that page, the voltage and current are rms average readings. They take no account of the relative phase between voltage and current. If you reverse the c.t. on its wire (or reverse its connections, or those of the a.c. adapter, but only one of these), then real power (which you’re not printing) will become positive - using our convention that means import/use, negative means export/generation - and so will power factor.

What sort of load do you have to give that power factor? If you’re using a pure resistance, e.g. an electric kettle or similar, it should be 1.00


(darrence avon) #9

ohh i see, thanks a lot ,i just did reverse my c.t on its wire and it is now giving me positive PF, :grinning:


(Noosha) #10

hi i have the same problem but i am using ACS712 20A current Senor ZMPT101B voltage senor directly connected to arduino

i changed the calibration as follow

emon1.voltage(A1, 580, 1.7); // Voltage: input pin, calibration, phase_shift
emon1.current(A0, 9.5); // Current: input pin, calibration.

v rms and I rms is right but real power and pf is not correct ( not equal to my wattmeter reading ) !!!

if any one can help >. please mail me
[email protected]


(Robert Wall) #11

We do not send email responses.

Have you carried out the full calibration procedure, in the “learn” section? If your voltage and current calibration is correct, but the phase/timing correction is wrong, then real power and hence power factor will be wrong. The default constant is the best value for the emonTx with the ‘shop’ voltage and current transformers. For anything else, you must determine the correct value by following the instructions for calibration.


(Sunny Stark) #12

hey there ,I have the same issue with power factor. I m using the same sensors as yous.have you solved the problem??


(Sunny Stark) #13

Is there any way to calculate real power using zmpt101 voltage sensor and acs 712 current sensor??
if possible please let me know.It would mean a lot. Thanks.


(Robert Wall) #14

If you use emonLib, then you will be able to calculate real power. You cannot use an emonTx because that expects a conventional current transformer and a.c. adapter, but you can use an Arduino or equivalent, one of our sketches and emonLib. You will need to make an interface for both devices that is the equivalent of the input circuitry described in ‘Learn’ - this for the acs712 and this for the zmpt101, that is, the input is a voltage not greater than 1.6 V rms and centred at +2.5 V d.c. You must calculate your calibration factors from the information here. (In short, the calibration factor is the current or voltage that would give you 1 V at the Arduino input.)


(Sunny Stark) #15

Thanks a lot… didn’t expect such a quick reply…
Thanks again :smiley::smiley:


(Sunny Stark) #16

So you are suggesting that the output parameters of both sensors must be same as the voltage and current sketches described in the site?? And I won’t have to alter the emon.lib ??


(Robert Wall) #17

Not exactly the same, but similar. You must not exceed 1.6 V rms at the input pin, and less if the input is not biassed to exactly 2.5 V d.c, but you can allow the voltage input to be somewhat less before you lose significant resolution. The current input is far more demanding, because it can vary over a wide range, and you need to have the output of your sensor as close to 1.6 V as possible at maximum current, so that you will be better able to measure small currents accurately.
(I’m assuming a 5 V Arduino here.)

Correct, you should have no need to alter emonLib. All the changes you need (calibration, input pins) can be done in its API.


(Sunny Stark) #18

Thanks again… I get it.:blush: