The datasheet shows a PGA gain accuracy of +/-4%!
Maybe they are using untrimmed metal film resistors on the chip. It's going to be calibrated anyway to account for the shunt tolerance in an electricity meter application.
Not the right tool for his job- which requires good DC accuracy and does not require simultaneous sampling.
--sp
Monumentally crappy...what page is that on in the spec sheet? :-)
I think it's usually in the absolute ratings section.
That's a lot of chip for a crummy RTD measurement, almost $11 at Mouser even.
We're paying $6.62 each, and they are very, very good. It's the heart of a multiplexed acquisition board that sells for around four kilobucks.
The fraction of our revenue that's due to parts cost has been declining over the years, partly because parts keep getting cheaper, partly because we have learned to use fewer of them.
Why are you always in such a bad mood? Is something wrong?
On 15/12/2015 06:29, Tauno Voipio wrote: >[...]
Interesting. It has lower input current than the LTC2444 which was on the board that I had to modify. I had to add input buffer op-amps because the ADC input current did cause much larger errors than the 0.05 degree error of the RTD itself.
Chris
Ok sorry, you knew what I meant. It does not reverse the thermocouple voltage but it reverses the effect on the resistance reading.
Chris
Even un-trimmed resistors should have a typical ratio accuracy of about
0.1% or so, at least for decent sized poly resistors. The absolute value might be 20% off but that shouldn't affect the gain in any sensible design.Chris
Care to explain what that tidbit of information has to do with less-than-brilliant approach of 16-/24-bit digitization of a ratio of resistance /derived/ voltages??? It might make sense if Vref was derived from another RTD, anything else is a wish.
Something us definitely wrong.
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