As shown in Fig having two temperature zones and thermocouple cold-junction compensation diode input circuit. This circuit uses the J-type thermocouple as a temperature sensor,
a semiconductor diode D is formed as a relatively cold junction compensation 0oC measurements, measuring temperature, T1 in the range of 0 ~ 1000oC. Temperature T2 is equal to the temperature of the semiconductor diode D TD. When measuring the temperature at 0 ~ 1000oC change, J-type thermocouple will have 58mV change. At an ambient temperature of + 25, the typical value 1.28mV. Corresponding to 0oC transmission current 4mA, corresponding to the current transmission + 1000oC is 20mA.