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vasant
Active Contributor

Join Date: Oct 2006
Posts: 16

True RMS to DC Conversion

10/30/2006 2:02 AM

i want to make a true rms to dc conversion circuit which will not have the problem of settling time usually associated with standard trms 2 dc converters like ad536 and the like.i need this because i want to make a welding controller and would like to carry out cycle to cycle correction with feedback control. the setling time of the ad536 adds to the delay of the control and introduces hunting.

anybody having ideas on this are welcome to suggest
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rcapper
Guru

Join Date: Dec 2005
Location: Etats Unis
Posts: 1871
Good Answers: 45
#1

Re: True RMS to DC Conversion

10/31/2006 2:48 AM

You can use a micro-controller that performs the same algorithm on a string of samples that span the desired time period. There was a good article in Circuit Cellar Ink on how to do the RMS math quickly with a micro-controller. I have used this method on numerous occasions and it works well. I used to use the AD536 as well. Also, I think some of AD's newer converters are faster than the '536 but it is definitely cheaper to use a micro. Your resolution is perhaps not as good but probably for welding you are not looking for a lab instrument.

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llizarraga
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Join Date: Jan 2006
Location: Panama
Posts: 58
#2
In reply to #1

Re: True RMS to DC Conversion

10/31/2006 12:59 PM

Hola. Do you have an electronic address to find this information? Regards

Luis
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rcapper
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Join Date: Dec 2005
Location: Etats Unis
Posts: 1871
Good Answers: 45
#3
In reply to #2

Re: True RMS to DC Conversion

10/31/2006 2:20 PM

You should be able to download the article at: www.circuitcellar.com.

The article was "Rooting Around" by Michael Dvorsky.

It was in issue 187 February 2006.

The article addressed performing integer square roots on small processors. You can then digitally perform the calculation that the AD536 does in analog. If you happen to have Analog Devices' "RMS to DC Conversion Application Guide" it covers the operation of the converters in great detail.

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llizarraga
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Join Date: Jan 2006
Location: Panama
Posts: 58
#4
In reply to #3

Re: True RMS to DC Conversion

10/31/2006 3:44 PM

Hola Rcapper. Thanks for your help. I will check the site. Regards.

Luis
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