At 09:57 PM 5/18/00 +0100, you wrote:
>I am wanting to read a thermocouple via a/d into a 'f873 but i am told that
>this is very difficult.
>
>I have the circuit to give 0-3.6 volts at .004v/oC from the therm, this
>gives a range of 0 to 900oC.
>
>How would i be able to read in and represent .28 volts in the pic ?
>


If I understand your question, you wish to use a thermocouple to measure
a temperature from 0 ~ 70'C, using a preamplifier designed for 0 ~ 900'C.
I would dissuade you from attempting this.

If you would still like to try, you should increase the amplification
of the preamplifier, and make proportional improvements in the isothermal
and tracking aspects of the cold-junction compensator, the TCVos drift
of the amplifier and the open-loop gain of the amplifier.

Of course you could always just stick a 15:1* or so amplifier on the
output of your preamp (to go into an on-board A/D), but the results
are quite likely to be rather disappointing in terms of both accuracy
and stability.

* you'd like to get as much range as possible of the A/D in use without
allowing the op-amp to saturate, so the gain depends on the amplifier etc.

Best regards,


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