The difference between pressure transmitter and temperature transmitter
1. Definition - Pressure transmitter:
It is a device used to measure the pressure of liquids, gases, or vapors, and convert these physical quantities into standard electrical signals (such as 4-20mA, 0-5V, etc.) for output. It is mainly used in the field of industrial automation to achieve remote monitoring and control- Temperature transmitter: It is a sensor used to measure the temperature of an object and convert the temperature signal into a standard electrical signal output. This type of transmitter is typically installed in various industrial environments that require monitoring temperature changes, such as chemical and food processing industries.
2. Working principle
pressure transmitter:
-Mechanical: The change in pressure is converted into displacement or deformation through elastic elements (such as Bourdon tubes, bellows, etc.), and then an electrical signal is generated by driving a potentiometer or other electrical components through a mechanical structure.
-Electronic: using principles such as piezoresistive effect, piezoelectric effect, and capacitance effect to directly convert pressure changes into electrical signals.
Temperature transmitter:
-Thermal resistance detector (RTD): measures temperature by utilizing the characteristic of metal resistance changing with temperature.
-Thermocouple: measures temperature based on the temperature difference electromotive force generated when two conductors of different materials are combined together.
-Semiconductor temperature sensor: measures temperature using the characteristic of the electrical resistivity of semiconductor materials changing with temperature.
3. Integrated temperature transmitter
The integrated temperature transmitter generally consists of a temperature measuring probe (thermocouple or thermistor sensor) and a two-wire solid-state electronic unit. The temperature probe is directly installed in the junction box in the form of a solid module, forming an integrated transmitter. Integrated temperature transmitters are generally divided into two types: thermistor and thermocouple.
The thermal resistance temperature transmitter is composed of a reference unit, R/V conversion unit, linear circuit, reverse protection, current limiting protection, V/I conversion unit, etc. After the thermal resistance signal is converted and amplified, the non-linear relationship between temperature and resistance is compensated by a linear circuit. After the V/I conversion circuit, a constant current signal of 4-20mA is output, which is linearly related to the measured temperature.
Thermocouple temperature transmitters generally consist of circuit units such as a reference source, cold junction compensation, amplification unit, linearization processing, V/I conversion, decoupling processing, reverse connection protection, and current limiting protection. It amplifies the thermoelectric potential generated by the thermocouple through cold junction compensation, eliminates the nonlinear error between thermoelectric potential and temperature through a linear circuit, and finally amplifies and converts it into a 4-20mA current output signal. To prevent 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 breaks or is poorly connected, the transmitter will output a ****** value (28mA) to cut off the power supply of the instrument.
The integrated temperature transmitter has the advantages of simple structure, wire saving, large output signal, strong anti-interference ability, good linearity, simple display instrument, solid module 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; Can be used in conjunction with microcomputer systems or other conventional instruments. Users can also request to make explosion-proof or fireproof measuring instruments.
4. Pressure transmitter
A pressure transmitter, also known as a differential transmitter, is mainly composed of pressure measuring elements, sensors, module circuits, display heads, watch cases, and process connectors. It can convert the received pressure signals of gases, liquids, etc. into standard current and voltage signals to supply secondary instruments such as indicator alarms, recorders, regulators, etc. for measurement, indication, and process adjustment.
The measurement principle of a pressure transmitter is that the process pressure and reference pressure are applied to the two ends of the integrated silicon pressure sensitive element, and the differential pressure causes the silicon wafer to deform (with a displacement of only μ m), so that the fully dynamic Wheatstone bridge made of semiconductor technology on the silicon wafer can output a mV level voltage signal proportional to the pressure under the drive of an external current source. Due to the excellent strength of silicon materials, the linearity and variation index of the output signal are both high. During operation, the pressure transmitter converts the measured physical quantity into a mV level voltage signal and sends it to a differential amplifier with high amplification and the ability to offset temperature drift. The amplified signal is converted into a corresponding current signal through voltage current conversion, and then subjected to nonlinear correction, finally generating a standard current voltage signal that corresponds linearly to the input pressure.
