AD59x Output Value not close to Expected Value

Document created by analog-archivist Employee on Feb 23, 2016
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My AD59x is not giving me anything close to the right output value. What
should I do?


The first thing you should check is the part’s behavior with both input pins
grounded. In
this configuration the part works as a temperature sensor. For example, if the
AD59x is
at 25 °C, you should see 250 mV at the output. If you put a warm finger on the
part, the
voltage output should rise. If this test fails, then check your power supplies,
connections, etc.
In most cases the above test will work correctly. This indicates your problems
are at the
thermocouple interface. The most common issues are:
1) Thermocouple leads swapped
2) Thermocouple not grounded correctly. See section on grounding.
3) Noise on long thermocouple leads being rectified by the part. See the
section on noisy
4) The AD59x is very far away from where the thermocouple enters the PCB board
cold junction.) The cold junction and the AD59x must be at the same temperature
– any
difference will show up directly as an error at the output.