Temperature Sensing and Control

This is a temperature indication and control system using the AD596/AD597. In this system, AD596/AD597 is used as a closed-loop thermocouple signal conditioner. This system uses an external op amp to implement setpoint. The advantages of this system are preserves the alarm function for open thermocouples and provides a high level (10mV/°C) output for the A/D panel meter. Here is the  schematic diagram of the circuit:

The A/D panel meter can easily be scaled and offset as shown to read directly in degrees Fahrenheit. The dominant residual errors will arise from two sources, if a two temperature calibration scheme is used. Those are thermocouple nonlinearity typical +1°C from –20°C to 350°C for type K and +1°C from 80°C to 550°C for type J, and also the ambient temperature rejection, typically ±2°C over a 25°C to 100°C range.

To increase the stability of the A/D converter this system uses an external voltage reference. Beside that, the external voltage reference is used to supply a stable reference for the setpoint voltage. [Source: analog.com]