Thermocouple Transmitters

Thermocouple transmitters are used extensively in industrial electronic circuits because the raw signal from the thermocouple is in the millivolt range (up to 80 mV). This small amount of voltage is not very useful until it's amplified. The transmitter provides a circuit that converts the signal to a 4-20 mA signal or a 0-10 volts signal. The transmitter also provides the circuitry to zero and span the thermocouple signal. The zero and span circuit consists of potentiometers that the technician can adjust to ensure that the signal is exactly 4 mA when it's at its minimum temperature, and exactly 20 mA when it's at its maximum temperature.

Above: An economical, type J, 4 to 20 mA transmitter. 4mA = 0°C. Adjust span via three selectable solder jumper positions. ach transmitter features an LED that increases in brightness with increasing current output. Transmitters require a 12-36 VDC loop power supply.