throbscottle
Well-Known Member
I've been working on designing the rms part of my little bench auto-ranging dmm project. It's based on a LTC1968 true-rms converter. This device takes a 1v peak differential input, and outputs up to 1v DC, where 1vrms in = 1vdc out, if I've understood everything correctly.
The auto-range up-switching was going to be triggered using the adc's over-range indicator, and I was going to amplify the rms converter's output so it would be able to reach the same level, and adjust the gain in the amp before the converter for the AC ranges, so all is tidy.
It occurred to me, after much head scratching, that I should be creating an auto-range trigger based on peak voltage, rather than the dc output from the rms converter, since voltage peaks could appear which are out of range, but don't develop enough rms value to show up higher than 1v on the converters output.
Creating a full-wave peak voltage detector (consisting of a full wave precision rectifier, comparator and voltage reference) takes quite a few extra components though, and I'm wondering if it's really worth doing.
So I'd really appreciate other people's thoughts on the matter, and what is the best way to go.
The project so far is a 6 digit, auto-ranging bench dmm, using a 24bit adc with a differential input range of 2.5v. Input is through a permanent divide-by-ten for protection, compensated by an amp to bring the level back up. I've got quite a lot of it up to a whole first version now!
Hope all that makes sense
TIA
The auto-range up-switching was going to be triggered using the adc's over-range indicator, and I was going to amplify the rms converter's output so it would be able to reach the same level, and adjust the gain in the amp before the converter for the AC ranges, so all is tidy.
It occurred to me, after much head scratching, that I should be creating an auto-range trigger based on peak voltage, rather than the dc output from the rms converter, since voltage peaks could appear which are out of range, but don't develop enough rms value to show up higher than 1v on the converters output.
Creating a full-wave peak voltage detector (consisting of a full wave precision rectifier, comparator and voltage reference) takes quite a few extra components though, and I'm wondering if it's really worth doing.
So I'd really appreciate other people's thoughts on the matter, and what is the best way to go.
The project so far is a 6 digit, auto-ranging bench dmm, using a 24bit adc with a differential input range of 2.5v. Input is through a permanent divide-by-ten for protection, compensated by an amp to bring the level back up. I've got quite a lot of it up to a whole first version now!
Hope all that makes sense
TIA