Transmitter type and classification

Sensors and transmitters play an important role in the field of instruments, meters and industrial automation. Different from the sensor, the transmitter generally has a certain amplification effect, in addition to converting non-electrical energy into measurable electricity.

Briefly introduce the characteristics and classification of various types of transmitters for users to choose.
â—† Integrated temperature transmitter:
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. Integrated temperature transmitters are generally classified into two types: thermal resistance and thermocouple type.
â–² RTD temperature transmitter is composed of reference unit, R/V conversion unit, linear circuit, reverse connection protection, current limit protection, V/I conversion unit and so on. After the temperature-resistor resistance signal is converted and amplified, the linear circuit compensates for the nonlinear relationship between temperature and resistance. After the V/I conversion circuit, a constant-current signal of 4-20mA linearly related to the measured temperature is output.

â–² Thermocouple temperature transmitter is generally composed of reference source, cold junction compensation, amplification unit, linearization, V/I conversion, burnout processing, reverse connection protection, current limiting protection and other circuit units. It is the thermal potential generated by the thermocouple through the cold junction compensation and amplification, and then cap the linear circuit to eliminate the non-linear thermal potential and temperature 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 measurement, 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.

The integrated temperature transmitter has the advantages of simple structure, saving lead wire, large output signal, strong anti-interference ability, good linearity, simple display instrument, solid module moisture resistance, reverse connection protection and current limit 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 of explosion-proof or fire-proof measuring instruments.

â—† Pressure transmitter:
Pressure transmitter, also called differential transmitter, is mainly composed of load cell sensor, module circuit, display meter, case and process connector. It can convert the received gas, liquid and other pressure signals into standard current and voltage signals to provide secondary instruments such as alarm indicators, recorders, and regulators for measurement, indication and process adjustment. Pressure transmitters are classified by measured object:

â–² Gauge Pressure Transmitter: Gauge Pressure Transmitter is a pressure transmitter with local atmospheric pressure as the reference zero point.

â–² Absolute pressure transmitter: Absolute pressure transmitter is a pressure transmitter with vacuum as the reference zero point. During use, the reference zero point of the sensor can be automatically adjusted without any correction according to the location of the location. The shape and gauge pressure transmitter are no different.
▲ Differential Pressure Transmitter: Differential pressure transmitter is a pressure transmitter that measures the pressure difference between two pressure chambers. Differential pressure transmitter has two pressure chambers, “+” and “-”. Respectively take the pressure of the two as the comparison value, usually the larger pressure end as "+" pressure chamber. Note: When ordering a differential pressure sensor, please note that one parameter specific to the differential pressure transmitter is static pressure resistance. For example, if the pressure transmitter of our application is used with a pressure of 10 MPa at the “+” pressure end and a pressure of 10.5 MPa at the “-” pressure end, then the differential pressure measured by the transmitter is: 10.5 -10=0.5MPa, the static pressure of the transmitter is 10MPa. In the application process, the use of high static pressure and low differential pressure are commonplace. The differential pressure transmitter ordered by the static pressure should not exceed the differential pressure transmitter's resistance to static pressure, otherwise, it is easily damaged.

â–² Input/Plug-in Level Transmitters: The level transmitters are divided into two types: input type and plug-in type. The two types are the same, which converts the pressure to liquid depth. When the water depth is 1m, the pressure on the transmitter is 10KPa. When ordering such sensors, pay attention:
(1) The density of the measured liquid should be reported to the production unit.
(2) When the measuring medium is corrosive, the production unit should be informed.
(3) The production unit is notified when the measured medium temperature exceeds -10°C and 60°C.
â–² medium and high temperature pressure transmitter: for the measurement of high ambient temperature or measurement medium temperature is too high, you must use high temperature pressure transmitter, the transmitter has a good zero temperature coefficient and temperature coefficient of sensitivity, in the temperature The measurement accuracy can be guaranteed in a high environment. When ordering this type of transmitter, it is necessary to inform the measuring medium temperature and the ambient temperature in order to facilitate the manufacturer's reasonable response.