RTD ultra precise signal conditioning

This isn't ultra-precise. A platinum resistance sensor changes by 0.4% per degree Kelvin, so your 0.02C is about 80ppm, and you could resolve it with a 14-bit A/D converter. Digitise the output of your sensor with a 24-bit sigma-delta A/D converter and your job is done.

Linear Technology sell a whole range of nominally 24-bit sigma-delta A/ D converters - they aren't accurate to more than 20-bits, but they spit out three 8-bit words.

For serious work you could use an AC excited sensor in a Blumlein (transformer) bridge, but that is a bit trickier.

-- Bill Sloman, Nijmegen

A good benchtop DVM with 4-wire ohms measurement would work. Some even include scanners and do the ohms-to-temperature conversion for you.

If you want to do it yourself, use a 2-channel delta-sigma ADC. Put the RTD in series with a very good resistor, apply a voltage, measure the two voltage drops, do the math. You can mux the RTDs into this, scan them, and as a bonus reduce self-heating. $20 in parts maybe.

John

Chetan, I don't know anything about the item whose temperature you wish to measure, which prevents me from any other useful comments.

Thank you all for the replies. I am sorry I forgot to mention that it was for water flowing through a pipe and the maximum temperature I will be dealing with wouldn't exceed 100 C. I did consider Bench top DVMs but most of them aren't rated for good ambient range (at the most 50C). I was hoping to find something DIN rail mountable and stable enough. I don't think the time frame will allow for designing the conditioning myself and that's why the search for a ready off the shelf module!

Does it have to be a platinum resistor? You can buy 0.1 C thermistors from YSI. They have lots more sensitivity than the Pt resistors.

George H.