Composition types of temperature transmitters

The integrated temperature transmitter is generally composed of a temperature probe (thermocouple or thermal resistor sensor) and a two-wire solid-state electronic unit. The temperature probe is directly installed in the junction box using a solid-state module to form an integrated transmitter. The integrated temperature transmitter is generally divided into two types: thermal resistor and thermocouple.

The thermal resistor temperature transmitter is composed of a reference unit, an R/V conversion unit, a linear circuit, reverse connection protection, current limiting protection, and a V/I conversion unit. After the temperature measurement thermal resistor signal is converted and amplified, the linear circuit compensates for the nonlinear relationship between temperature and resistance, and outputs a 4-20mA constant current signal that is linearly related to the measured temperature after the V/I conversion circuit.

The thermocouple temperature transmitter is generally composed of a reference source, cold end compensation, amplification unit, linearization treatment, V/I conversion, disconnection treatment, reverse connection protection, current limiting protection, and other circuit units. It is to amplify the thermoelectric potential generated by the thermocouple through the cold end compensation, and then eliminate the nonlinear deviation between the thermoelectric potential and temperature by the linear circuit, and finally amplify and convert it into a 4~20mA current output signal. In order to avoid accidents caused by temperature control failure due to thermocouple wire breakage during thermocouple measurement, the transmitter is also equipped with a power-off protection circuit. When the thermocouple wire is broken or the connection is poor, the transmitter will output the maximum value (28mA) to cut off the power supply of the instrument.

The integrated temperature transmitter has the advantages of simple structure, saved leads, large output signal, strong anti-interference ability, good linearity, simple display instrument, solid module anti-seismic and moisture-proof, reverse connection protection and current limiting protection, and reliable operation.

The output of the integrated temperature transmitter is a unified 4~20mA signal; it can be used in conjunction with a microcomputer system or other conventional instruments. Users can also request to make it into an explosion-proof or fireproof measuring instrument.