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i am making a temperature controller using zilog z8 microcontroller.sensor is J type thermocouple.what would be the best ADC ?
also how is the process value obtained from the digital value?
using assembly language
What do you mean by multipoint?
If you mean that you will need to measure the Temp in more than one place you shuld use the ADC0808 by National Semiconductors , it has 8 channels and its pretty simple to work with...
Basically, you have to measure the voltage at the thermocouple junction and convert that voltage to temperature using the standard thermocouple tables (ITS-90). This table is available from the Omega website or from NIST in the USA. In software, you may use a lookup table.
However, in connecting to the thermocouple, you can't avoid producing other thermocouple junctions which in turn produce their own voltages. You have to compensate for this. This is known as cold junction compensation. Info on how to do this can be found in the above mentioned websites.