With the continuous expansion of production scale and the development of production technology, higher and higher requirements have been put forward for the automation level of the production process. Therefore, industrial instruments have also undergone a development process from scratch, from simple to complex, from single function to multifunctional. From on-site measurement and display of temperature (such as glass thermometers), pressure (such as U-tube pressure gauges), flow rate (such as glass rotor flow meters), and liquid level (such as glass tube level gauges), as well as on-site regulators that can only perform simple control, it has gradually developed towards remote transmission, centralized display, and remote control. In addition to more complete detection components and instruments for detecting various parameters, the development of process control instruments is also advancing rapidly, experiencing a leap from QDZ, electrical unit combination instruments, electronic integrated control devices to industrial computer control systems.

There are many types of industrial automation instruments, which can be divided into five categories based on the processes of information acquisition, transmission, reflection, and processing. (1) Testing instruments; (2) Display instrument; (3) Control instruments; (4) Execution agency; (5) Centralized monitoring device.

(1) Measuring instruments

During the production process, the physical quantities such as temperature, pressure, flow rate, and material level of the media in different parts of the equipment and pipelines are rapidly changing and always changing. Measuring instruments are used to measure the magnitude of the aforementioned physical quantities at each moment.

According to the different process parameters being tested, detection instruments can be divided into the following types.

1. Temperature instruments: Commonly used temperature measuring instruments include glass thermometers, bimetallic thermometers, pressure (temperature pack) thermometers, temperature switches, thermocouples, and resistance thermometers, as well as radiation thermometers such as radiation pyrometers, optical pyrometers, and photoelectric colorimetric pyrometers.

2. Pressure gauge: Pressure measuring instruments are used to detect pressure, vacuum, and differential pressure. According to its working principle, it can be divided into: elastic pressure gauge (according to its elastic components, it can be divided into spring tube pressure gauge, diaphragm pressure gauge, diaphragm pressure gauge, pressure switch, etc.); Sensing pressure gauges (such as resistive, capacitive, inductive, Hall pressure gauges, etc.); Liquid column pressure gauges (such as U-tube, straight tube, and inclined tube pressure gauges); There are also high-precision piston pressure gauges, which are usually used to calibrate standard pressure gauges.

3. Flow meters: There are many types of flow measurement instruments. Currently, throttling devices and their corresponding differential pressure flow transmitters are widely used. The commonly used throttling devices include orifice plates, nozzles, and Venturi tubes. Other commonly used flow meters include water meters, rotor flow meters, elliptical gear flow meters, target flow meters, electromagnetic flow meters, vortex flow meters, Anuba flow meters, mass flow meters, etc.

4. Level gauge: The level gauge mainly measures the liquid level of a certain medium or the interface between two liquids with different densities, as well as the liquid level of solid materials in towers, tanks, and tanks. ***Common level gauges include glass tube level gauges and glass plate level gauges, as well as differential pressure level gauges and buoyancy level gauges (such as float level gauges, level switches, float level gauges, float level gauges, steel strip level gauges, tank level weighing instruments, etc.) Solid material level detection adopts resistance level gauge, capacitance level gauge, level switch, heavy hammer detection level gauge, tuning fork level gauge, ultrasonic level gauge, and radioactive level gauge.

5. Composition analyzer: The composition analyzer is used to verify the composition of the process medium and determine the content of certain components (or some components up to all components). According to their working principles, they can be divided into electrochemical analyzers (such as conductivity meters, industrial acidity meters, zirconia analyzers, etc.), thermal analyzers (such as thermal conductivity analyzers, thermochemical molecular analyzers, infrared analyzers), magnetic permeability analyzers, photoelectric colorimetric analyzers, mass spectrometers, industrial gas chromatographs, etc.

When installing an online component analyzer, it is generally necessary to preprocess the sample to ensure that its state, temperature, pressure, flow rate, and other parameters meet the requirements of the analyzer's working conditions. Therefore, it is necessary to configure some pipeline systems, including filters, dust collectors, drying containers, coolers, rotor flow meters, water seals, valves, and pipelines. In order to perform general pre-treatment on the sample. For some special media (such as smoke polluted gas samples, high-temperature gas samples such as furnace gas, heavy oil analysis sampling, corrosive component sampling, environmental detection sampling, etc.), the sampling and preprocessing system is more complete. This type of finished product sampling preprocessing system is called a sampling preprocessing device.

In addition, some physical testing instruments such as hygrometers, hygrometers, density meters, density meters, turbidity meters, viscosity meters, etc. are often classified as component analysis instruments.

6. Mechanical measuring instruments: Commonly used industrial machinery measuring instruments include thickness gauges, thermal expansion detectors, tension detectors, deflection detectors, shaft vibration, shaft displacement, speed detection devices, rotating machinery weighing devices (such as large steam turbine compressors, etc.) (such as electronic belt scales, belt deviation and slip detection devices, weighing display devices, weighing bag reassembly devices, etc.)

(2) Display instrument

This type of instrument is used to indicate or record the instantaneous value of the measured parameter, such as ratio meters, millivolt meters and other dynamic indicators, digital indicators, electronic potentiometers, electronic balance bridges (electronic potentiometers and balance bridges can also be combined with electric or pneumatic regulators), used to indicate or record temperature, and integrated instruments with flow accumulation function.

(3) Control instruments

On the one hand, the control instrument receives measurement signals from process detection instruments and transmitters for display, and on the other hand, sends adjustment signals to control the action of the actuator (actuator and regulating valve), forming a closed-loop control system.

Control instruments can be divided into analog control instruments and digital control instruments according to signal types.

1. Analog control instruments include basic instruments, unit combination instruments (pneumatic and electric), and combination instruments.

(1) Unit combination instruments are divided into different units based on their functions in the control system. Each unit instrument exists independently and can be combined into different detection and adjustment systems as needed. The system composition is flexible and convenient. Unified standard signal (also known as analog signal) is used for signal transmission between units. Combination instruments were widely used in the 1950s and early 1970s as a truly decentralized instrument that uses one instrument to perform a required function.

It should be noted that the transmission unit instrument (excluding temperature transmitters) in the unit combination instrument should function as a detection instrument.

Combination instruments can be divided into QDZ and electric combination instruments according to their working energy.

Qdz: QDZ is developed on the basis of the original pneumatic instruments. This type of instrument uses 0.14MPa compressed air as its working energy and 0.02~0.1 MPa compressed air as its unified signal. Due to its working energy and signal transmission being compressed air, the application of pneumatic unit instruments in refining and chemical production facilities has a natural explosion-proof effect. Its disadvantage is that the transmission distance of pneumatic signals is generally within 150m, and when the transmission distance is too far, the signal transmission lags, affecting the sensitivity of display adjustment. Qdz includes the following unit instruments:

A. The transmission unit (i.e. transmitter) includes pressure transmitter, differential pressure transmitter, target flow transmitter, built-in orifice flow transmitter, single (double) flange differential pressure (liquid level) transmitter, internal (external) float level transmitter, temperature transmitter, etc.

B. Display unit instruments, such as strip indicators, bar indicators, multi pin indicators, indicator recorders, accumulators, etc.

C. The regulating unit instruments include indicator regulators, recording regulators, cascade regulators, proportional (integral, derivative) regulators, etc.

D. Computational instruments such as addition and subtraction devices, multiplication and division devices, ratio devices, etc.

E. Given unit instruments, such as setting devices, time program setting devices, etc.

F. Auxiliary device instruments, such as pneumatic (Q-type) operators, manual/automatic switching operators, high (low) value selectors, relays, switches, limiters, proportional devices, load distributors, high flow filters, and pressure reducing valves.

F. Auxiliary device instruments, such as pneumatic (Q-type) operators, manual/automatic switching operators, high (low) value selectors, relays, switches, limiters, proportional devices, load distributors, high flow filters, and pressure reducing valves.

Electric combination instrument: The electric combination instrument uses DC power as its working energy. This instrument has gone through three development stages: Type I (electronic tube circuit), Type II (transistor circuit), and Type III (linear integrated circuit) due to the upgrading of its basic electronic components. At present, Type I and Type II have been phased out and are no longer in use. Type III is still widely used in refining and chemical production facilities. The electric unit combination instrument introduced now only refers to Type III. The Type III electric instrument is powered by a DC24V power supply. The signal transmission between the various unit instruments installed in the control room uses DC1-5V voltage signals, while the current signal between the instruments in the control room and the on-site transmission instruments, regulating valves, and actuators is DC4-20mA. In order to meet different explosion-proof requirements, the transmitters installed on site and the input/output units (safety brackets, safety barriers) connected to them in the control room are divided into explosion-proof and intrinsic safety types. In addition, due to the development of industrial computer control technology, intelligent unit instruments with microprocessors as the core have been developed in recent years, becoming a new force in electrical unit instruments.

The electrical unit combination instrument includes the following units:

A. The transmission unit (i.e. transmitter) includes pressure transmitter, differential pressure transmitter, target flow transmitter, built-in orifice flow transmitter, single (double) flange differential pressure (liquid level) transmitter, internal (external) float level transmitter, temperature (temperature difference) transmitter, intelligent pressure transmitter, intelligent differential pressure transmitter, etc.

B. Display unit instruments, such as single (double) needle indicators, strip indicators, single (double) needle alarms, single (double) note recorders, multi-point indicator recorders, proportional (root) accumulators, etc.

C. The regulating unit instruments include indicator regulators, SPC/DCD backup regulators, multi-channel valve position tracking regulators, special function regulators, integrators, differentiators, etc.

D. Computing unit instruments such as addition and subtraction, multiplication and division, square root, etc.

E. Conversion unit instruments include current signal converters, pulse/voltage converters, frequency/current converters, impedance converters, function converters, electric/gas converters, gas/electric converters, etc.

F. The given unit instrument includes constant current setter, ratio setter, ratio setter, alarm setter, parameter program setter, time program setter, etc.

G. Auxiliary device instruments, such as electric (D-type) operators, DDC operators, safety brackets, safety barriers, power distribution devices, voltage boxes, signal selectors, isolators, inverters, elevators, signal dampers, signal inverters, signal limiters, rate of change selectors, etc.

(2) Assemble integrated control instruments

It is a new series in the development of process control instruments, also known as prefabricated integrated control devices. It adopts a component-based structure, which can conveniently and flexibly form process control systems. The system adopts a 0-10V DC voltage signal system. On site detection instruments and components that can also receive various pneumatic and electrical signals (including current, voltage, contacts, pulses, frequency, codes, etc.).

The assembled integrated control device includes the following instruments and components:

A. Input/Output Components: Input Conversion Components, Output Conversion Components, Pulse Conversion Components, mV/V Conversion Components, P/E Conversion Components, Integrated Power Driver Components, etc.

B. Signal processing components: signal buffering components, relay buffering components, signal generation components (ramp generation components, timing components, etc.), analog computing components (multiplication and division components, root cutting components, addition components, function components, limiting components, signal selection components, etc.), integration components, alarm components, logic components.

C. Adjustment components: PID components (proportional, integral, derivative components), dynamic compensation components, tracking components, multi output interface components, sound and light control components.

D. Auxiliary components and other components: power distribution components, signal distribution components, switch components, given components, relay components, and monitoring components.

E. Display operation instruments: single (double) needle indicator, single (double) note recorder, three (four) note recorder, trend recorder, manual operator, and control display operator.

(3) Basic type regulating instrument

In the development process of industrial automation instruments from on-site detection and display to centralized control, a type of instrument that integrates measurement, display, and regulation functions has emerged, which we call basic regulating instruments or simply basic instruments. For example, indication and recording regulators with pneumatic regulators, as well as some local regulators with a single regulating function (such as temperature regulators, pressure regulators, differential pressure regulators, and flow regulators). According to the different working energies, the baseline adjuster can be divided into pneumatic and electric types.

Self operated regulating valve is also a type of on-site regulating instrument. Named after relying on the measured medium as its working energy, it is also known as a direct acting regulator. In addition, since it is integrated with its regulating valve, the self operated regulating valve is also called a self operated regulating valve. The commonly used self operated regulating valves include self operated temperature regulating valves, self operated pressure regulating valves, and self operated flow regulating valves.

2. Digital control instruments

Digital control instruments include distributed control systems (DCS), programmable logic controllers (PLC), industrial control machines (IPC), safety control systems (FSC), etc.

In the 1960s, with the large-scale and complex industrial production processes, industrial automation control systems were required to not only process large amounts of data, but also achieve * * operation control, facilitate information exchange, achieve centralized display operation and * * * control, and improve control accuracy. Simply using conventional analog instruments cannot meet the above requirements, so a computer control system is adopted to further improve the comprehensive control level of the production process. However, with the high concentration of control functions, the risk of accidents is also highly concentrated. Once the computer control system malfunctions, control, monitoring, and operation will be unable to proceed, causing significant impact on production and even leading to major global accidents.

After the 1970s, with the emergence of large-scale integrated circuits and the birth of microprocessors, a new process control system based on microprocessors and microcomputers was developed on the basis of further development in control technology, display technology, computer technology, and communication technology, such as DCS (Distributed Control System). The decentralized control system inherits the advantages of conventional analog instruments and computer control systems. Based on centralized display operation and management, it disperses control power and further improves the safety and reliability of the control system. This is because distributed control systems allocate microprocessors based on control functions or control areas. Each control station with a microprocessor can control several or dozens of circuits, and several control stations can be combined to control the entire production process, achieving the goal of decentralized control and risk dispersion. On this basis, a large amount of information is sent to the microprocessor based CRT display operation station in the central control room through data communication cables for centralized display or recording of information. Simultaneously cooperate with the upper computer (process management computer and production management computer) to implement centralized monitoring and management of the production process.

Distributed control systems can achieve continuous control, batch (intermittent) control, sequential control, data acquisition and processing, and * * * control, closely integrating operation management with production processes. The distributed control system also has a self diagnostic function, which can check the hardware and software of the system. Once a fault is detected, it will sound and light an alarm and display the location of the fault.

Distributed control systems generally consist of peripheral devices such as on-site control stations, CRT display operation stations, communication networks, printers, etc.

In the subsequent development process, the control communication function of the distributed control system became increasingly perfect and standardized, and according to the focus of its control function, the programmable logic controller (PLC) with sequence control as the main function was separated from the distributed control system (DCS) with loop control as the main function. The original purpose of PLC was to replace the relay interlocking alarm system composed of traditional relays. Its input/output signals are all switch signals. It uses software programming methods to perform functions such as logic, sequence, timing, counting, and calculation, and is suitable for complex interlocks. The characteristic of PLC is "programmable", and the control scheme can be changed by changing the program. Its reliability, flexibility, operating speed, and complexity of control schemes are unmatched by relay circuits.

The development of PLC has been very rapid, enhancing simulation control and calculation functions, and even equipped with CRT dynamic graphic display, database management, file generation and other functions. DCS, on the other hand, incorporates the technical features of PLC and enhances the functions of batch processing and sequential control. The penetration of these two functions will narrow the difference between DCS and PLC, making the logo blurry. With the continuous development of distributed control systems, especially in small and miniaturized systems, intelligent field transmitters, fieldbus standardization, communication network standardization, DCS and PLC mutual penetration, and further improvement of system software, distributed control systems will be more suitable for various applications.

Fieldbus (FCS) is a digital, serial, multi-point communication data bus installed between production site equipment and control room automatic control equipment. The basic idea is that the DCS and PLC control stations, as well as intelligent regulators in the control room, are no longer connected to field instruments (such as transmitters, regulating valves, switches, etc.) through their respective input/output (I/O) channels. They only need to be connected to the H2 high-speed channel of the field bus through their respective serial interfaces, and then connected to the H1 field bus through the H2/H1 exchange bridge, thereby achieving communication between H1 and H2 field instruments and monitoring and detecting the production process.

Due to the integration of field control and field communication functions in the communication network of the underlying field devices (field devices and field instruments) of fieldbus, the nodes of the fieldbus communication network are intelligent transmitters (including temperature, pressure, flow, material level, process analyzers, etc.) and intelligent actuators.

Industrial computers are divided into basic automation control devices and management computers according to their control and management functions, with basic automation devices being multi pole control. ***The levels include distributed control system (DCS), programmable logic controller (PLC), direct digital control device (DDC), and fieldbus control system (FCS). The process management computer is the upper computer of the basic automation device and belongs to the second level of multipole control. Production management computers are suitable for the third to fifth stages of multipolar control.

(4) Actuator

An actuator, also known as a control valve, consists of an actuator and a valve. According to the power source of the actuator, it is divided into four categories: pneumatic control valves, electric control valves, hydraulic control valves, and hybrid control valves. Pneumatic control valves are divided into diaphragm control valves, piston control valves, and long stroke control valves according to their actuator forms.

(5) Centralized monitoring device

A centralized detection device is a device that uses detection elements or detectors to display the measured variable or alarm contact signal in a centralized manner; A centralized control device is a device that controls a series of measured variable signals to actuators based on a set program. The centralized monitoring device includes various data acquisition devices, patrol detection devices, signal alarm devices, safety detection devices, industrial television, remote control devices, and sequential control devices. Centralized monitoring equipment is generally divided into the following categories:

1. Safety monitoring devices include combustible gas detection and alarm devices, toxic gas detection and alarm devices, flame detectors, automatic ignition devices, combustion safety protection devices, oil leakage detection devices, and high resistance detection devices.

2. Industrial television consists of cameras and their ancillary equipment (lighting, blowing, cooling devices, and electric turntables), displays, and auxiliary equipment (operators, distributors, compensators, switches).

3. The remote control device receives input variable signals, processes the information, displays an alarm on the screen, and outputs control signals to the control terminal.

4. Signal alarm devices include various types of signal alarm devices such as flash alarm devices, intelligent flash alarm devices, relay line alarm systems, etc.

5. The sequence control device includes relay interlocking protection system, logic monitoring device, sequence control device, and intelligent sequence controller.

6. Data collection and inspection alarm devices include data collection devices and inspection alarm devices.

(6) Automatic control of other devices

This type of equipment mainly includes various (channel type, cabinet type, frame type, screen type) instrument panels, instrument boxes, operation consoles, insulation (protection) boxes, power boxes, etc.

(7) Self control materials

Self control materials refer to the various types of materials required for instrument installation, such as pressure pipelines (seamless steel pipes, stainless steel pipes, high-pressure pipes), gas supply pipelines (galvanized steel pipes, brass pipes), gas signal pipelines (copper pipes, copper pipe cables, nylon pipe cables, junction boxes), electrical pipeline materials (welded steel pipes, galvanized steel pipes), valves, flanges and fittings in various pipelines, and electrical equipment materials for self-control.