K type thermocouple amplifier circuit1

Have a customer ask xiamen branch's son yesterday manager K type thermocouple with what the king of the op-amp is better? I need to measure 0 Temperature of 500 degrees? Cold junction compensation do better? I want to use single chip microcomputer 10 AD collection. This problem is less incisive, without abundant professional knowledge average person return true answer. The following simple explanation.

general use LM324 and IC7650 thermocouple op-amp, cold junction compensation in a copper heat resistance of 51 ohms series circuit access bridge arm.

in theory is based on the cold end in zero standard measurement, however, usually when measuring instrument is under room temperature, due to the cold end is not zero, causing the thermoelectric potential difference decreases, and the measurement, there is an error. The compensation measures is the cold junction compensation.

when the thermocouple measuring temperature to the cold end ( Measure the end for the hot end, by the end of the lead connected to the measurement circuit is called cold junction) Temperature remains constant, the size of thermoelectric potential and measured temperature in certain proportion relationship. When measuring, the cold end ( Environment) Changes in temperature, will be affected the accuracy of measurement. Take action at the cold end compensation due to the impact of the cold end temperature change is called the thermocouple cold junction compensation.

the thermocouple cold junction compensation usually adopt the cold end in a composed of thermal resistance bridge in series. The three bridge arms for standard resistance, in addition, there are a bridge arm by ( Copper) Thermal resistance. When the cold end temperature change ( Rise, for example) Thermocouple thermoelectric potential will change (to produce Reduce) Series, while the heat resistance of bridge resistance will also change and make the change at the ends of the bridge voltage also ( Higher) 。 If the parameter is a good choice and wiring is correct, produced by the bridge voltage as it happens and thermoelectric potential changes over temperature equal to the amount, the thermocouple measurement circuit, the total output voltage ( Potential) Exactly reflect the measured temperature value.