I haven't used thermocouples.
I guess I'm tolerably familiar with the Crystalfontz 633 and the Dallas Semiconductor / Maxim IC ds18b20 thermometers. ( BB2K is definitely correct in suggesting that you calibrate them.
http://dbserv.maxim-ic.com/appnotes....te_number/1117 # App Note 208: Curve Fitting the Error of a Bandgap-Based Digital Temperature Sensor - DS18B20 The math in that is not something that I'm particularly versed in. My gerneral sense is that the ds18b20's varry... As I write: three taking temp into radiator are within .15 deg. C of each other, three on the rad out within a .12 deg. C range -- and one of 8 air temps always seems to read a whopping 3 C high no matter how I arrange them. The last time I orderd from maxim they were $2.28 apiece, so culling out a few deviants from a bundle is quite affordable. ( I have ~10 on the shelf ) Last time I tried to focus on calibrating a set, I was overwhelemed by how much more effect the mounting of the sensors had than the error in the sensors. In my case: how well was each sensor measuring the water versus measuring the that which held it in the water. I'm actually feeling thick-headed on the topic at the moment and am wondering what's on sci-fi ...
A flowmeter with a 4-20 milliamp pulsed output in a range compatible with fan rpm outputs I've found to be convenient for automatic data logging.
http://www.omega.com/ppt/pptsc.asp?r...000&Nav=gref02 is what I'm using. Mine is a tad askew -- I ran watter wetter through it and I think something in that kept causing a low grade nylon bushing to swell and sieze. I haven't had one in my hands or talked to anyone who has used one but I've been window shopping for a doppler or vortex-shedding or magnetic induction flowmeter. The zero moving parts appeals to me. I can imagine ( quite hypothetically for me as a hobbyist here ) swapping in the 5th waterblock into a test bench for the day, wondering if the flow seems low as reported by a turbine or paddlewheel meter, finding some sliver of hose trimmings or whisp of teflon tape stuck to the turbine, and asking myself "now how much data should I throw out?"
things on my window shopping list:
http://www.flocat.com/products/index...eries&sid=161&
http://www.clarksol.com/html/prodspecsDM_01D.htm
http://www.thorntoninc.com/products_pfa.htm