How to amplify circuits with K-type thermocouples

Thermocouple amplifiers typically use LM324 and IC7650, while cold end compensation uses a 51 ohm copper thermistor connected in series to the bridge arm circuit.
In theory, measurement is based on the cold end being at zero degrees. However, when measuring, the instrument is usually at room temperature. Due to the non zero temperature of the cold end, the thermoelectric potential difference decreases, resulting in inaccurate measurement and errors. The compensation measure taken is cold end temperature compensation
When measuring temperature with a thermocouple, it is required that the temperature of its cold end (the measuring end is the hot end, and the end connected to the measuring circuit through a lead is called the cold end) remains constant, so that the magnitude of its thermoelectric potential is proportional to the measured temperature. If there is a change in the temperature of the cold end during measurement, it will seriously affect the accuracy of the measurement. Taking certain measures at the cold end to compensate for the impact caused by temperature changes at the cold end is called cold end compensation for thermocouples.
The cold end compensation of thermocouples usually uses a bridge composed of a thermistor connected in series at the cold end. The three arms of the bridge are standard resistors, and the other arm is composed of (copper) thermistors. When the temperature at the cold end changes (such as increases), the thermoelectric potential generated by the thermocouple will also change (decrease), and at this time, the resistance value of the thermoelectric resistance in the series bridge will also change and cause the voltage at both ends of the bridge to change (increase). If the parameters are selected well and the wiring is correct, the voltage generated by the bridge is exactly equal to the amount of change in thermoelectric potential with temperature, and the total output voltage (potential) of the entire thermocouple measurement circuit accurately reflects the measured temperature value.