A temperature transmitter is an instrument that converts a temperature variable into a standardized, transmissible output signal. Utilizing thermocouples or thermal resistors as sensing elements, the signal generated by the sensor is fed into the transmitter module. Following processing through circuits for voltage regulation and filtering, operational amplification, non-linear correction, V/I conversion, constant current control, and reverse polarity protection, the signal is converted into a standardized output-typically a 4–20 mA current signal, a 0–5 V or 0–10 V voltage signal, or an RS485 digital signal-that bears a linear relationship to the measured temperature.
Essentially, it is a device that converts physical measurement signals or standard electrical signals into a standardized electrical output, or outputs data via a communication protocol. Temperature transmitters are primarily employed in industrial processes for the measurement and control of temperature parameters. A current transmitter, conversely, converts the AC current flowing through a main measurement circuit into a standardized constant-current loop signal, which is then continuously transmitted to a receiving device.
A temperature-to-current transmitter specifically converts the signal from a temperature sensor into a current signal; this signal is then fed into a secondary instrument (such as a display or controller) to indicate the corresponding temperature reading. For instance, if the temperature sensor in the accompanying diagram is a PT100 model, the function of the temperature-to-current transmitter is to convert the sensor's resistance signal into a current signal, which is subsequently input into the instrument to display the measured temperature.