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Originally Posted by bigben2k
Thanks DrMemory, I suspected as much, but could not find any info to that effect.
Otherwise, I've always suspected that a 4 wire pRTD would more than likely be my best/only choice, for reducing the noise, short of working with candlelight... (which is still not out!) but again, I can find no info about the actual resolution that I might be able to extract from an RTD probe or element.
Again, I'm not looking to measure an absolute temperature, just a temperature differential. I fully realize that I have no hope of getting to an absolute reading with a resolution of 0.001 deg C, at least not without spending an insane amount of money.
I'm not looking to use the full bit range of the 24 bit ADC, just enough to be able to pick up the differential temperature between two probes with a resolution of 0.001 deg C. The temp range would be between 20 and 50 deg C. (differential would be water temp to heat die temp, maybe 20 deg C max?) Incoherent's 0.002 (18 bit) is the closest suggestion I've seen yet.
Does anyone (other than M. Grumpy  ) have a feel about if this can be done, say with 2 * pRTD 4-wire probes? |
Ben, I'll try to answer without sounding like BillA. Think of your error budget. First, remember that errors add in quadrature, then think of all your errors. How stable/precise is the current source you use to read the RTD's? How much is the self heating effect in your RTD's,? What is the precision/accuracy of your DAQ? (and then read the Analog Devices tech notes on accuracy vs bits of resolution)
And then do a few test calibrations with a crock pot and 4 or 5 sensors to get a feel for the scatter. Perform fits to ALL the sensors and then figure the errors for each sensor from the fit. Then see how you fit your error budget of .001 degree. I told you that .03 was very doable, .01 is hard, .001 and you are a god.
And if you want to skip to the chase Cole Palmer does sell matched 0.01 RTD's for $209 each.
Cheers