The integrated temperature transmitter has the advantages of simple structure, large output signal, saving lead, good linearity, strong anti-interference ability, simple display instrument, solid-state module anti-seismic and moisture proof, reverse connection protection and current limiting protection, and reliable work. 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. Can also be made according to user requirements explosion-proof or fire-resistant measuring instruments.
The integrated temperature transmitter generally consists of a temperature probe (thermocouple or RTD sensor) and a two-wire solid electronic unit. The solid-state module is used to mount the temperature probe directly in the junction box to form an integrated transmitter. The integrated temperature transmitter is generally divided into two types: thermocouple and thermal resistance.
The thermocouple temperature transmitter is generally composed of a reference source, a cold junction compensation, an amplifying unit, a linearization process, a V/I conversion, a burnout processing, a reverse connection protection, and a current limit protection circuit unit. It is the thermal potential generated by the thermocouple through the cold-end compensation after amplification, and then cap the linear circuit to eliminate the thermal potential and temperature of the nonlinear error, and finally amplified into 4 ~ 20mA current output signal. In order to prevent accidents caused by temperature control failure due to galvanic disconnection in thermocouple measurements, a power failure protection circuit is also provided in the transmitter. When the thermocouple breaks or fails to connect properly, the transmitter will output the maximum value (28mA) to make the meter cut off the power.
Thermal resistance temperature transmitter is composed of R/V conversion unit, reference unit, reverse connection protection, linear circuit, current limiting protection, V/I conversion unit and so on. After the temperature-resistor resistance signal is converted and amplified, the linear circuit compensates the nonlinear relationship between the temperature and the resistance. After the V/I conversion circuit, a constant current signal of 4-20 mA linearly related to the measured temperature is output.