Current loop transmitter is the term associated with sensor system that is used in industrial 4-20mA current loop technology. This transmitter contain the signal conditioning circuit for the sensor (chromel-alumel thermocouple), and a current regulator to maintain the current loop to consistently represents the sensor reading. Here is the schematic diagram of the circuit:
When dealing with thermocouple, the feature of cold junction compensation in this circuit make it close to perfect, although it still has small non linear error. The internal voltage reference provided by the LM10 enable the design to be compact and simple, suitable for many loop-powered transmitter application.