A temperature transmitter is used to transmit the measured temperature as an analogue signal to a receiver.
A temperature transmitter transmits a measured temperature as an analogue 0/4–20 mA signal to a receiver. The receiver will typically be an electronic regulator or PLC (Programmable Logic Controller).
A PLC is a small computer that is not normally able to directly measure electrical signals from a sensor. The temperature transmitter is fitted with a resistor with either PT or NTC resistance.
PT and NTC
The terms PT and NTC are abbreviations for positive and negative temperature, and describe whether resistance in the resistor is increasing or falling as the temperature rises. If a resistance sensor is connected directly to the receiver, the resistance in the wire between the two components is also measured and will give a false reading. The bias is dependent on the length of the wire and the ambient temperature.
Temperature transmitters are used to avoid voltage loss, or when a regulator or PLC cannot directly measure the signal from a resistance sensor.