Book Analog Interfacing to Embedded Microprocessors
the (temperature-sensitive) drop across the semiconductor junction.
The amplifier used to increase the signal level from the thermocouple is
usually an instrumentation amp. The gain required to measure a thermo-
couple is typically in the range of 100 to 300, and any noise picked up by the
thermocouple will be amplified by the same amount. An instrumentation
amplifier rejects the common mode noise in the thermocouple wiring.
Analog Devices makes a thermocouple signal conditioner, the AD594/
595, which is specifically intended for interfacing to a thermocouple. The
AD594/595 does not use an external semiconductor junction to compensate
for connection temperature; instead the part includes an internal junction
that is expected to be the same temperature as the connection. Consequently,
the thermocouple connection must be made on the PC board, close to the
AD595/595 package.
Figure 3.4
Thermocouple.
annaabi.ee 
