There are many types of industrial automation instruments, which can be divided into five categories based on the process of information acquisition, transmission, reflection and processing.
Testing instruments
During the production process, the temperature, pressure, flow rate, level, and other physical quantities of the medium at different parts of the equipment and pipelines are constantly changing. Monitoring instruments are used to detect the values of these physical quantities at each instant.
According to the different process parameters being measured, the measuring instruments can be divided into the following types:
1. Temperature instruments:
Commonly used temperature measuring instruments include glass thermometers, bimetallic thermometers, pressure (temperature bulb) thermometers, temperature switches, thermocouples, resistance thermometers, as well as radiation thermometers, optical thermometers, photoelectric colorimetric thermometers, and other radiation thermometers.
2. Pressure gauges:
Pressure measuring instruments are used to detect pressure, vacuum, and differential pressure. Based on their working principle, they can be classified as: elastic pressure gauges (further classified according to their elastic element, such as Bourdon tube pressure gauges, diaphragm pressure gauges, capsule pressure gauges, pressure switches, etc.); sensor pressure gauges (such as resistive, capacitive, inductive, and Hall effect pressure gauges); liquid column pressure gauges (such as U-tube, straight tube, and inclined tube pressure gauges); and piston pressure gauges, which have higher accuracy and are typically used to calibrate standard pressure gauges.
3. Flow meter:
There are many types of flow measurement instruments, but the most widely used are throttling devices and their matching differential pressure flow transmitters. Commonly used throttling devices include orifice plates, nozzles, and venturi tubes. Other commonly used flow instruments include water meters, rotor flow meters, oval gear flow meters, target flow meters, electromagnetic flow meters, vortex flow meters, anuba flow meters, and mass flow meters.
4. Level instruments:
Level gauges primarily measure the liquid level of a specific medium or the interface between two liquids of different specific gravities, as well as the level of solid materials, within towers, tanks, and other containers. The most common level gauges are glass tube level gauges and glass plate level gauges. Other types include differential pressure level gauges and buoyancy level gauges (such as float level gauges, level switches, float-type level gauges, buoy level gauges, steel strip level gauges, and tank level weighing instruments). For solid material level detection, there are resistance level gauges, capacitive level gauges, level switches, weighted level gauges, tuning fork level gauges, ultrasonic level gauges, and radioactive level gauges.
5. Component analysis instruments:
Component analysis instruments are used to verify the composition of process media and determine the content of a certain component (or some components or even all components). According to their working principle, they can be divided into electrochemical analyzers (such as conductivity meters, industrial pH meters, zirconia analyzers, etc.), thermal analyzers (such as thermal conductivity analyzers, thermochemical analyzers, infrared analyzers), and magnetic permeability analyzers, photoelectric colorimetric analyzers, mass spectrometers, industrial gas chromatographs, etc.
When installing online component analysis instruments, it is generally necessary to pre-treat the samples to ensure that parameters such as sample state, temperature, pressure, and flow rate meet the operating requirements of the analysis instrument. Therefore, a piping system consisting of filters, dust collectors, drying containers, coolers, rotor flow meters, water seals, valves, and pipelines is required for general sample pre-treatment. For some special media (such as flue gas, furnace gas, heavy oil analysis samples, corrosive component samples, and environmental monitoring samples), the sampling pre-treatment system is more sophisticated; this type of pre-packaged sampling pre-treatment system is called a sampling pre-treatment device.
In addition, some physical property testing instruments, such as moisture meters, hygrometers, densitometers, concentration meters, turbidity meters, and viscometers, are often classified as component analysis instruments.
6. Mechanical measuring instruments:
Commonly used mechanical measuring instruments in industry include thickness gauges, thermal expansion testers, tension testers, deflection testers, as well as shaft vibration, shaft displacement, and speed detection devices and weighing devices (such as electronic belt scales, belt misalignment and slippage detection devices, weighing displays, weighing and bagging devices, etc.) used for rotating machinery (such as large steam turbine compressors).
Display Instrument
This type of instrument refers to instruments used in conjunction with measuring instruments to indicate or record the instantaneous value of the measured parameter, such as moving coil indicators like ratio meters and millivoltmeters, digital displays, and electronic potentiometers and electronic balance bridges for indicating or recording temperature (electronic potentiometers and balance bridges can also be combined with electric or pneumatic regulators to form composite instruments), as well as totalizing instruments with flow accumulation functions.
Control Instruments
The control instrument receives and displays measurement signals from process detection instruments and transmitters, and sends adjustment signals to control the actions of actuators (actuators and control valves), forming a closed-loop control system.
Control instruments can be divided into two main categories based on signal type: analog control instruments and digital control instruments.
1. Analog control instruments
Analog control instruments include base-mounted instruments, unit combination instruments (pneumatic, electric) and modular instruments.
Pneumatic unit combination instrument
As industrial automation instruments evolved from local detection and display to centralized control, a type of instrument integrating measurement, display, and regulation functions emerged, which we call a base-type regulating instrument or simply a base-type instrument. Examples include indicating and recording regulators with pneumatic regulators and some local regulators with only a single regulation function (such as temperature regulators, pressure regulators, differential pressure regulators, and flow regulators).
2. Digital control instruments
Digital control instruments include distributed control systems (DCS), programmable logic controllers (PLC), industrial control computers (IPC), and safety control systems (FSC).
Actuator
An actuator, also known as a control valve, consists of two parts: an actuator and a valve. Based on the power source of the actuator, control valves are classified into four main categories: pneumatic control valves, electric control valves, hydraulic control valves, and hybrid control valves. Pneumatic control valves are further classified according to the type of their actuator: diaphragm control valves, piston control valves, and long-stroke control valves.
Centralized monitoring and control device
A centralized detection device is a device that uses detection elements or detectors to centrally display the measured variable or alarm contact signal; a centralized control device is a device that controls the actuator according to a set program of a series of measured variable signals. Centralized monitoring and control devices include various data acquisition devices, patrol detection devices, signal alarm devices, safety detection devices, industrial television and remote control devices, and sequence control devices, etc.
Centralized monitoring and control devices are generally classified into the following categories:
1. Safety monitoring devices include combustible gas detection and alarm devices, toxic gas detection and alarm devices, flame monitors, automatic ignition devices, combustion safety protection devices, oil leak detection devices, and high resistance detection devices, etc.
2. Industrial television consists of a camera and its auxiliary equipment (lighting, purging, cooling devices and electric turntable), a display and auxiliary equipment (operators, distributors, compensators, switchers), etc.
3. The remote control device receives the input variable signals, processes the information, displays the 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 flashing signal alarms, intelligent flashing alarm devices, and relay alarm systems.
5. Sequence control devices include relay interlocking protection systems, logic monitoring devices, sequence control devices, and intelligent sequence controllers, etc.
6. Data acquisition and patrol detection alarm devices include data acquisition devices and patrol detection alarm instruments, etc.
Automatic control of other devices
These types of equipment mainly include various types (channel type, cabinet type, frame type, screen type) of instrument panels, instrument boxes, control consoles, insulation (protection) boxes, power supply boxes, etc.
Self-controlled materials
Automatic control materials refer to the materials required for instrument installation, which are numerous and varied, such as pressure-conducting piping (seamless steel pipes, stainless steel pipes, high-pressure pipes), gas supply piping (galvanized steel pipes, brass pipes), gas signal piping (copper pipes, copper cables, nylon cables, connection boxes), electrical piping materials (welded steel pipes, galvanized steel pipes), valves, flanges and fittings in various piping systems, materials for automatic control electrical equipment (cables, wires, junction boxes, electrical equipment and components), instrument cable trays, angle steel, channel steel and other structural steel materials used to make instrument equipment supports and brackets, heat tracing and insulation materials, and anti-corrosion painting materials, etc.
