The lumped parameter system, specifically the thermal lumped parameter system of a thermocouple is like so:
- is my the temperature of the target body.
- is what I sense.
- ==The thermocouple is characterized by a very small capacitance (), since it is a conductive metal==.
- The rest is a standard thermal circuit with : ambience temperature.
- Becouse of thermal coupling and thermal capacitances, this gives you always a temperature which is different from .
- Tho there are some strategy for obtaining good measurement, so this problem can be neglected.
And we have already seen that there is a possibility of performing an ACJC (automatic cold junction compensation), using for example an RTD sensor.
- The front-end will contain another sensor, and a Voltage amplifier (we suppose a slow-varying signal)
We suppose to operate with slow varying quantities, because usually the temperature doesn’t vary fast.
So we are operating with DC coupled amplifier.