The law generates an analog output signal to push the actuator to eliminate the deviation, so that the controlled parameter is kept near a given value or changes according to a predetermined law. In automation instruments, instrument valves are often used to synthesize the output signals of detection instruments to achieve the purpose of controlling the production process. The adjusted parameters include temperature, pressure, flow, liquid level, composition and so on. Classification of instrument valves Instrument valves produce analog output signals according to the law used to push actuators to eliminate deviations, so that the controlled parameters remain near the given values u200bu200bor change according to predetermined rules. In automation instruments, instrument valves are often used to synthesize the output signals of detection instruments to achieve the purpose of controlling the production process. The adjusted parameters include temperature, pressure, flow, liquid level, composition and so on. Instrument valve classification Instrument valves are divided into three categories: pneumatic instrument valves, hydraulic instrument valves and electric instrument valves according to the energy used; according to the principle and structure, they can be divided into self-operated instrument valves, base-type regulating instrument valves, simple regulating instrument valves, Unit combination instrument valve and assembled integrated control device, etc. (see picture). The instrument valve is divided into two-position instrument valve, proportional instrument valve, PI instrument valve (proportional integral instrument valve), PID instrument valve (proportional integral differential regulator), feedforward instrument valve, etc. according to the regulating function. ①Self-operated instrument valve' uses the energy of the adjusted medium itself or after a simple conversion to drive the regulating valve to realize automatic adjustment. Float-type liquid level regulators (such as those used in toilets) use the buoyancy of the float on the liquid surface to make the regulating valve act. This kind of regulator does not require external energy and is an on-site regulating device. It is simple in structure, easy to maintain, and suitable for single-parameter adjustment systems that do not require high control accuracy. It is very similar to a pneumatic actuator in principle and structure, and is often classified as an actuator. ②Base-type instrument valve an indicating and recording instrument with additional adjustment mechanism. It receives the signal from the detection element, and drives the adjustment mechanism to send out a control signal by the action of the instruction and recording mechanism, which is sent to the actuator to realize automatic adjustment. Moving-coil indicating and regulating instruments, electric and pneumatic recording instruments with electric or pneumatic regulators are all of this type, and they are widely used to control a single production equipment. Simple instrument valve a kind of regulating instrument that can directly receive the signal of the detection element, without indicating mechanism, with strong specificity and simple structure. It can also receive the signal from the transmitter. Both non-indicating regulators and temperature alarms are simple regulating instruments, which are widely used in small and medium-sized enterprises. ④Unit combination meter a set of regulating meters composed of several standard units with independent functions. It is fully adapted to the requirements of large-scale units and process control, and can realize complex control of multiple loops (see electric unit combination instrument, pneumatic unit combination instrument). ⑤Assembled integrated control device 'Assembled instrument for short, it is a special control device composed of various independent functional components according to the requirements of a large-scale unit or process control. It can be assembled according to the needs of users, so it has great flexibility.
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