Hi all,
I need to measure an AC voltage between 1Vac to 3Vac pic to pic and convert the results to a RMS voltage.
I know that diode is ineffective at this precision, I need to measure by 5 millivolt max.
I know that is not an easy task.
Please, can you help me? Some guidance would be very appreciated.
Study the possibilities given by OP-Amp circuitry.
Railroader:
Study the possibilities given by OP-Amp circuitry.
Hi Railroader, thanks for reply. The OP-amp topic is very wide. Please, can you give me more narrow informations?
Search "precision rectifier".
JCA34F:
Search "precision rectifier".
Precision rectifier - Wikipedia
Hi JCA34F, thank you for your answer, I am going to check it.
I have to say that is measurement should be done at 3khz fixed.
chacouet:
Hi JCA34F, thank you for your answer, I am going to check it.
I have to say that is measurement should be done at 3khz fixed.
Beware! You still need to calibrate your voltmeter, no matter how you design it.
Paul
Paul_KD7HB:
Beware! You still need to calibrate your voltmeter, no matter how you design it.
Paul
Hi Paul, thanks for the comment.
I need to measure an AC voltage between 1Vac to 3Vac pic to pic and convert the results to a RMS voltage.
I assume you mean peak-to-peak?
I need to measure by 5 millivolt max.
So, where does that come-in? Is that the resolution/precision? With the 10-bit ADC there are 1024 "steps" so with the default 5V reference you get approximately 5mV of resolution (~5mV/step).
And, you can bias the input with a voltage divider (2 equal-value resistors) and a DC "blocking" capacitor.
If you know it's a sine wave there is a known ratio between the RMS & peak values. so you just have to find the peak. If it's an arbitrary wave shape you'll have to do an actual RMS calculation.
True RMS-to-DC Converter = AD737, ......
DVDdoug:
I assume you mean peak-to-peak?So, where does that come-in? Is that the resolution/precision? With the 10-bit ADC there are 1024 "steps" so with the default 5V reference you get approximately 5mV of resolution (~5mV/step).
And, you can bias the input with a voltage divider (2 equal-value resistors) and a DC "blocking" capacitor.
If you know it's a sine wave there is a known ratio between the RMS & peak values. so you just have to find the peak. If it's an arbitrary wave shape you'll have to do an actual RMS calculation.
Hi DVDdoug, thank you for your precisions.
-yes, peak to peak, sorry for the typo.
Yes, it is the minimum precision I need.
-Yes, it is a sine wave only.
Find the pic, it sounds straightforward. Please, what kind of Op-amp configuration I need to detect the peak?
Vik321:
True RMS-to-DC Converter = AD737, ......
Hi Vik321, thank you for this info. It seems to suit my needs and, answers to my precedent message to DVDdoug (peak detection). 
I will test this way. Have a great day all! 
Try this one.
https://circuits4you.com/2016/05/13/ac-current-measurement-acs712/
You don't need a sensor, use this configuration.
Measuring small voltages = noise problem = smoothing.
Hi Vik321,
Big Thank! 
Hi all,
I can get go max to 10mV resolution, as predicted
Because I need 5 mV resolution, it's not enough.
What could I do to increase the resolution by 10? 1mV would be helpful.
What may be the options to achieve it?
Hi,
Can you show us what circuit your are using to get where you are now?
Have you got a project running?
What components are you using?
Thanks.. Tom...
TomGeorge:
Hi,
Can you show us what circuit your are using to get where you are now?
Have you got a project running?
What components are you using?Thanks.. Tom...
Hi Tom,
I used the same assembly that showed Vik321.
Yes.
I used the same components and values used on his drawing.
Hi,
What controller and what code?
Proper complete circuit will help?
For better resolution you will need an ADC with higher bit count.
Tom...
TomGeorge:
Hi,
What controller and what code?
Proper complete circuit will help?
For better resolution you will need an ADC with higher bit count.Tom...
I use the UNO board.
The complet circuit is the one I told you. It didn't work on simulation but, with real component it works. What can I say more?
For a better resolution I need an ADC, okay thank you Tom...
What if I use 16 bit series instead of 8 bit series directement to A0? Could it work?
your resolution is 5V/1024 = about 5 mV, first you need to get stable readings then increase resolution if its need more than 5 mV, there is two ways, A - using delays, B - smoothing.
Vik321:
your resolution is 5V/1024 = about 5 mV, first you need to get stable readings then increase resolution if its need more than 5 mV, there is two ways, A - using delays, B - smoothing.
Hi Vik321, thank you for you precisions.
I have a stable reading, but according to the sketch used, I does not give better precision than 0.01. I tried to use a long but, I may have done it in the wrong way because it does not bring more precisions.
- Using delay... Do you mean slowing down the reading?
- Smoothing? I don't know what you mean by this. Please, can you explain me a little more?