A regulator that uses an analog signal is also called an analog regulator. It determines the deviation between the measured value of the controlled object parameter in the analog form and the given value, and generates an analog output signal according to a certain regulation law to push the actuator to eliminate the deviation, so that the controlled parameter remains near the given value or changes according to a predetermined law. In automation instruments, regulating instruments 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.
According to the energy used, analog control instruments are divided into three categories: pneumatic instruments, hydraulic instruments and electric instruments; according to the principle and structure, they can be divided into self-operated regulators, base-type regulators, simple regulators, unit combination instruments and assembled models. Integrated control device, etc. (see figure). Analog regulating instruments are divided into two-position regulators, proportional regulators, PI regulators (proportional integral regulators), PID regulators (proportional integral differential regulators), feedforward regulators, etc. according to their regulating effects.
①Self-operated regulator” uses the energy of the medium to be adjusted or after 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 pneumatic actuators in principle and structure, and is often classified as actuators.
②Base-type adjustment instrument an indication 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 for 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.
③Simple adjustment instrument A kind of adjustment instrument that can directly receive the signal of the detection element without indicating mechanism, 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 Instrument is a set of regulating instruments 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” is abbreviated as an assembled instrument, which is a special control device combined with 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.
Development direction The future development of analog regulating instruments roughly has the following aspects:
①Diversified control functions According to the requirements of equipment operation, not only various feedback control functions (such as proportional integral, proportional integral derivative, etc.), but also new regulation laws (such as feedforward control, adaptive control, nonlinear control, etc.) ), program control and various interlocking protections.
②The expansion of system function The change of production process and production scale requires that the automatic adjustment instrument can adapt to various single parameter and multi parameter control systems, and can easily expand the control function and system scale.
③Compatibility between analog instrument and computer Computer control must establish connection with analog instrument. For example, when using direct digital control, some key loops are commonly used as a backup with analog regulators. When using set value control, analog regulators are needed to control the production process. Therefore, it is necessary to solve the problem of combining analog instruments with computers.
④Ease of operation and safety and reliability. With the emergence of many large-scale, high-efficiency process equipment, automatic control systems have become increasingly complex, and more and more regulating instruments are used. For example, for a 300,000 kilowatt generator set with a transistor-type unit combination instrument control, the control panel is more than 10 meters long, and there are more than 400 operating handles.
The unit can start up for 10 hours, and the operator is very burdened. Therefore, simple operation is required for the new regulating instrument. In addition, many large-scale industrial devices work in critical conditions and have extremely high requirements for the reliability of automatic control. The regulating instrument should cooperate with the monitoring and protection devices of the entire system to make the entire system operate safely and reliably.