Author Topic: Any IC for measuring RMS voltage?  (Read 1401 times)

0 Members and 1 Guest are viewing this topic.

Offline ManxTopic starter

  • Contributor
  • Posts: 39
  • Country: pl
Any IC for measuring RMS voltage?
« on: June 10, 2020, 10:24:58 am »
I need to measure RMS voltage of pulsed DC, in the range up to ~100 mV, with at least 16 bit resolution, from two channels, and output it via I2C (preferably) or SPI. Supply is 3.3 V. I don't want to calculate the RMS voltage myself and I'd like to use some ready-made integrated solution.

Unfortunately, I cannot find any IC that could do this. I only found some RMS-to-DC converters, that I could put before the existing slow ADC interfacing with slow and small microcontroller. These converters are however very expensive compared to the cost of other components (and I'd need two of them). Also, at least the ones I found, need dual supply.

Do you know of any IC that may be of use to me?
 

Offline dzseki

  • Frequent Contributor
  • **
  • Posts: 524
  • Country: hu
Re: Any IC for measuring RMS voltage?
« Reply #1 on: June 10, 2020, 10:47:16 am »
For a pulsed DC signal (that is a square wave in nature) the RMS is the same as the average, and you can obtain the average by a simple low pass filtering, no?
HP 1720A scope with HP 1120A probe, EMG 12563 pulse generator, EMG 1257 function generator, EMG 1172B signal generator, MEV TR-1660C bench multimeter
 
The following users thanked this post: Manx

Offline coromonadalix

  • Super Contributor
  • ***
  • Posts: 7014
  • Country: ca
Re: Any IC for measuring RMS voltage?
« Reply #2 on: June 10, 2020, 11:26:57 am »
You have the famous ad636 or ad637 used in multimeters ?
 
The following users thanked this post: Manx

Offline ManxTopic starter

  • Contributor
  • Posts: 39
  • Country: pl
Re: Any IC for measuring RMS voltage?
« Reply #3 on: June 10, 2020, 01:54:40 pm »
By "pulsed" I mean rectified AC. Or worse.

@coromonadalix , AD636 was what I had in mind when I was thinking about RMS-to-DC converters. The problem is, when used with a single supply, it requires 5 V. I have only 3.3 V.

BTW, are they really famous and used in multimeters? Like, are they THE chips for the job?
 

Offline Wytnucls

  • Super Contributor
  • ***
  • Posts: 3045
  • Country: be
Re: Any IC for measuring RMS voltage?
« Reply #4 on: June 10, 2020, 02:19:42 pm »
AD 736/737
Wide power supply range: ±2.5 V to ±16.5 V
 

Offline coromonadalix

  • Super Contributor
  • ***
  • Posts: 7014
  • Country: ca
Re: Any IC for measuring RMS voltage?
« Reply #5 on: June 10, 2020, 02:31:59 pm »
You can use icl 7660  to do some voltages conversions, like creating negatives voltages ...


For the rms converters chips, Maxim as a few, Intersil too,  but in the end they do the same jobs, unless you have very specific needs / use ?
« Last Edit: June 10, 2020, 02:34:40 pm by coromonadalix »
 
The following users thanked this post: Manx

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 15157
  • Country: de
Re: Any IC for measuring RMS voltage?
« Reply #6 on: June 10, 2020, 03:56:08 pm »
There are also chips made for power meters. These usually have some 2  ADCs and some DSP function to calculate the true power. An example would be the ADE7753, but there are others too.

Many of them also offer direct RMS and similar readings.  These chips are quite powerful and due to the large numbers they are used in metering they are surprisingly cheap.
 
 
The following users thanked this post: Manx

Offline Benta

  • Super Contributor
  • ***
  • Posts: 6420
  • Country: de
Re: Any IC for measuring RMS voltage?
« Reply #7 on: June 10, 2020, 04:20:19 pm »
For a pulsed DC signal (that is a square wave in nature) the RMS is the same as the average, and you can obtain the average by a simple low pass filtering, no?

Umm, no.

 

Offline ManxTopic starter

  • Contributor
  • Posts: 39
  • Country: pl
Re: Any IC for measuring RMS voltage?
« Reply #8 on: June 10, 2020, 09:14:49 pm »
Thank you very much for your help.

Thanks for pointing me towards ICL7660. I think for now I will use it with AD736 to make the current prototype work with pulsed DC.

Thanks for pointing me towards power meters. I found MCP39F521 and it looks nice at the first glance. I'll probably use it (or something like it) in the future as they are very cheap and seem to do what I want.
 

Offline schmitt trigger

  • Super Contributor
  • ***
  • Posts: 2431
  • Country: mx
Re: Any IC for measuring RMS voltage?
« Reply #9 on: June 10, 2020, 09:21:08 pm »
The LTC1966 is rated for a supply voltage of 2.7 to 12 volt.
« Last Edit: June 10, 2020, 09:22:51 pm by schmitt trigger »
 
The following users thanked this post: Manx

Offline ManxTopic starter

  • Contributor
  • Posts: 39
  • Country: pl
Re: Any IC for measuring RMS voltage?
« Reply #10 on: June 10, 2020, 11:10:09 pm »
Thanks VERY much! LTC1966 seems like the way to go.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf