An integrated 4-20 mA two-wire transmitter with intrinsic temperature sensing capability

An integrated two-wire transmitter which converts signals from temperature sensors, resistance temperature detectors (RTDs), and thermocouples into an industrial standard 4-20 mA output is discussed. This transmitter is unique in that it is a silicon temperature sensor with a standard output which also allows compensation for the cold junction of thermocouples. The device is p-i-n programmable to perform different functions of signal conditioning and has been implemented on a standard bipolar linear IC process. Measured samples of an experimental chip configured as an RTD-signal conditioner have shown an accuracy of 0.1% and a nonlinearity of 0.02%. As a temperature sensor over the range 0.85 degrees C, the TWT has been accurate within +or-1 degrees C.>