>I need to learn to use thermocouples, and am looking for thermocouple >interface designs and/or chips to minimize the effort I simply roll my own. The main question is : what kind of accuracy do you need? How do you want to calibrate? Can you tolerate the inherent non-linearity of a K type TC? Its a 7th order polynomial if you want fractional degree accuracy. I use a silicon diode to measure cold junction temperature - you wind up with a large offset that must be subtracted. You then calibrate gain if needed. One series of TC transmitters we build (several thousand each year) gets trimmed for offset during test - we just stuff a 1% resistor as determined by the test jig. Gain is not trimmed since I only need 1-2% accuracy. This transmitter is based upon the LM10 from Nat Semi - its got fairly low open loop gain which limits the final accuracy anyways. Another TC preamp uses software and eeprom to hold both offset and gain calibration. Its based upon a 12ce673's 8 bit a/d and uses dither to get 14 bit resolution (accuracy is only good to about 10-11 bits) and 24 bit integer math. A large portion of the dynamic range (25%) is eaten up by the offset - I end up with 1 degree accuracy over the range of 0 - 650 F. This one is still under development - I expect the final version to be even more accurate with some added software filtering. In both cases (and in all my other pre-amps / transmitters), I use the -2.1 mV / degree C temperature response of a 1n4148 to measure cold junction temperature. This is divided down to 40.5 uV / degree C to match the K type TC that I am using and summed with the TC signal. My op-amp of choice is now the AD8551 (brand new and just excellent). Current designs that use the LM10 will continue to do so but new designs are all gonna switch to the AD part. This should get you started - ask more questions as they come up. dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.