An integrated temperature transmitter typically consists of a temperature probe (thermocouple or RTD sensor) and a two-wire solid state electronics unit. The temperature probe is mounted directly in the junction box in the form of a solid module to form an integrated transmitter. Integrated temperature transmitters are generally classified into two types: thermal resistance and thermocouple type.
The thermal resistance temperature transmitter is composed of a reference unit, an R/V conversion unit, a linear circuit, a reverse connection protection, a current limiting protection, a V/I conversion unit, and the like. After the temperature-measuring thermistor signal is converted and amplified, the nonlinear relationship between the temperature and the resistance is compensated by the linear circuit, and a constant current signal of 4-20 mA which is linear with the measured temperature is output after the V/I conversion circuit.
The thermocouple temperature transmitter is generally composed of circuit elements such as reference source, cold junction compensation, amplification unit, linearization processing, V/I conversion, burn-off processing, reverse connection protection, and current limiting protection. It is to compensate the thermoelectric potential generated by the thermocouple through the cold junction compensation, and then the nonlinear error of the thermoelectric potential and the temperature is eliminated by the linear circuit, and finally amplified and converted into a 4-20 mA current output signal. In order to prevent accidents caused by temperature control failure due to galvanic breakage in the thermocouple measurement, the transmitter also has a power-off protection circuit. When the thermocouple breaks or the connection is poor, the transmitter will output the maximum value (28mA) to turn off the power.
The integrated temperature transmitter has the advantages of simple structure, saving lead wires, large output signal, strong anti-interference ability, good linearity, simple display instrument, anti-seismic and moisture-proof of solid modules, reverse connection protection and current limiting protection, and reliable operation.
The output of the integrated temperature transmitter is a uniform 4 to 20 mA signal; it can be used with a microcomputer system or other conventional instruments. It can also be made into explosion-proof or fireproof measuring instruments.
