K-type thermocouple cold junction compensation circuit composed of INA114

Shown is a K-type thermocouple cold junction compensation circuit composed of INA114 . INA 114 has
been introduced in the second section of this chapter.
    Since a thermocouple is made by connecting two different conductors to form a junction, thermoelectric potential will be generated when the temperatures at both ends of the junction are different .
Because of this, when the thermocouple is far away from the amplifier and a wire is needed to connect them
, the wire becomes part of the thermocouple (also sensitive to temperature). The temperature environment of this part is
often different from that of the thermocouple. The temperature environment of the thermocouple itself is different, which will affect the output signal of the thermocouple, resulting in
temperature error. Therefore, in circuits with high measurement accuracy, wires or cold junctions need to be compensated to eliminate detection
errors.
    The cold junction, also known as the reference junction, refers to the thermoelectric potential at o'c. In the figure, the two nodes of the thermocouple
are in the same temperature environment as the temperature-sensing diode VD1. At 0℃, adjust RL so that the output vo=0.oov, then
the cold junction is corrected. When the junction temperature changes, the temperature of VD1 also changes, and the voltage at both ends changes accordingly. This change is added to both ends of the thermocouple
and its cold junction through R2 and the core to compensate for the change in junction temperature . Influence. AD5 81 provides a reference voltage of IO. OOV, and Rc adjusts the gain of the amplifier.