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Why do you use a reference voltage for each CT?

(Oscar Puyal) #1

First of all sorry for my English it is not as goos as I would like it to be

I need to know the power consumption of several points (14) and I have studied the design of the hardware to optimize it. I have a heatpump board working in Zaragoza (Spain)

My first question is: why do you use a reference voltage for each CT instead of use the same (1,65 V) for all of them (CT1, CT2 and CT3)? I think this has multiple advantages for the hardware but also for the software

Kind regards
Oscar

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(Robert Wall) #2

Cost, I think. If you have 14 inputs, then it makes much more sense to use a common 1.65 V bias supply, best provided by an op.amp. See https://learn.openenergymonitor.org/electricity-monitoring/voltage-sensing/acac-buffered-voltage-bias

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(Oscar Puyal) #3

Thanks Robert for your answer. You’re very kind

Let me show you the circuits scheme. I am testing it in the laboratory an it works really well.

https://github.com/onsar/onsave/blob/master/hardware/shield_v01/gerber/ciruit_scheme.pdf

Notice the ref_medida is for all the CTs (yhdc sct-013-000) the same

Best regards

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(Robert Wall) #4

As the FAQ says:
Please don’t link to files on external sites. Unlike others, we want you to attach your screenshots, log files, etc to your post. If the external site goes away, the material is likely to be lost forever. If that happens, when someone reads your post, your question and our answer will have little or no value.
If you need to post more than one attachment, tell us you have more information to post, and we’ll change your user account settings to enable you to do so.

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(Oscar Puyal) #5

Sorry Robert but I am trying to upload the file but the system tells me:

“Sorry, new users can not upload attachments”

Please let me know what i have to do to upload the file

Kind regards
Oscar

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(Robert Wall) #6

You should be able to do it now, I’ve raised your membership level.

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(Oscar Puyal) #7

This is the schema I was talking about
ciruit_scheme.pdf (78.2 KB)

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(Robert Wall) #8

I cannot see an operational amplifier there to give a low impedance voltage source for the mid-point bias supply (ref_medida). I think you might have a problem with the signal on one channel also appearing at a low amplitude on the others.

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(Oscar Puyal) #9

Yes, that’s my concern and that’s why I’m testing the previous circuit but, in the tests I’m doing, the input signal from a CT has no influence on the others.
An operational circuit would be safer but if there really is no difference it does not make sense.

Thank you very much for your support.

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