There are many classification methods for detection and process control instruments (usually called automation instruments ), and corresponding classification can be performed according to different principles. For example, according to the energy used by the instrument , it can be divided into pneumatic instrument, electric instrument and hydraulic instrument (rare); according to the combination of instruments, it can be divided into base instrument, unit instrument and comprehensive control device; installed according to instrument The form can be divided into field instruments, panel-mounted instruments and rack-mounted instruments; with the vigorous development of microprocessors, according to whether the instrument has introduced a microprocessor (device), it can also be divided into intelligent instruments and non-intelligent instruments. According to the form of instrument signal, it can be divided into analog instrument and digital instrument.
Display instruments can be divided into recording instruments and indicating instruments, analog instruments and digital display instruments according to the functions of records and instructions, analog and digital. Among them, the recording instruments can be divided into single-point recording and multi-point recording. (Multi-point and multi-point), among which there are paper records or paperless records, if there are paper records, they are divided into transcripts and print records.
The adjusting instrument can be divided into a base type adjusting instrument and a unit combined type adjusting instrument. Due to the introduction of microprocessors, there are programmable controllers and fixed-program controllers.
The actuator consists of an actuator and a regulating valve. The actuators are divided into pneumatic actuators, electric actuators and hydraulic actuators according to their energy sources. According to the structure, they can be divided into film type, piston type (cylinder type) and long stroke actuators. Regulating valves are classified according to their structural characteristics and flow characteristics. According to the structural characteristics, there are usually straight-through single seat, straight-through double seat, tee, angle, diaphragm, butterfly, ball valve, eccentric rotation, sleeve (cage), valve. Volume separation, etc., is divided into straight lines, logarithms (equipartition ratio), parabola, and quick opening according to the flow characteristics.
This type of classification method is relatively reasonable, and the coverage of the instrument is relatively wide. However, any one of the classification methods cannot classify all the instruments in a well-organized manner, and there is penetration and communication between them. For example, the transmitter has multiple functions. The temperature transmitter can be classified as a temperature detection instrument, the differential pressure transmitter can be classified as a flow detection instrument, and the pressure transmitter can be classified as a pressure detection instrument. The position can be classified as a level detection instrument, it is difficult to accurately classify it, and the calculation and auxiliary units in the combined instrument of the Chinese and foreign units are also difficult to merge.