There are many types of industrial automation instruments. From the process of information acquisition, transmission, reflection and processing, industrial automation instruments are divided into five categories.

Detection instrument

During the production process, the temperature, pressure, flow, level and other physical quantities of the medium in different parts of the equipment and pipelines are changing rapidly and are always changing. The detection instrument is used to detect the value of the above-mentioned physical quantity at each instant.

According to the measured process parameters, the detection instruments can be divided into the following types:

1. Thermometers:

Commonly used temperature measuring instruments include glass thermometers, bimetallic thermometers, pressure (temperature bulb) thermometers, temperature switches, thermocouples, thermal resistances, radiation pyrometers, optical pyrometers, photoelectric colorimetric pyrometers and other radiation thermometers.

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, bellows pressure gauge, pressure switch, etc.); sensor pressure gauge (such as resistance type, Capacitive, inductive, Hall pressure gauges, etc.); liquid column pressure gauges (such as U-tube, straight pipe, inclined pipe pressure gauges); and piston type that is usually used to calibrate standard pressure gauges with higher accuracy pressure gauge.

3. Flow meter:

There are many types of flow measuring instruments, and the most widely used one is the throttling device and its matched differential pressure flow transmitter. Commonly used throttling devices are orifice plates, nozzles and venturi tubes. Other commonly used flow meters include water meters, rotameters, oval gear flow meters, target flow meters, electromagnetic flow meters, vortex flow meters, Anuba flow meters, mass flow meters, etc.

4. Level instrument:

The level meter mainly measures the level of a certain medium in towers, tanks and tanks, or the interface of two liquids with different specific gravity and the level of solid materials. The most common level gauges are glass tube level gauges, glass plate level gauges, and other differential pressure level gauges and buoyancy level gauges (such as float level gauges, liquid level switches, float level gauges) Gauge, buoy level gauge, steel belt level gauge, tank level weighing instrument, etc.). For solid material level detection, there are resistance level gauges, capacitive level gauges, level switches, weight detection level gauges, tuning fork level gauges, ultrasonic level gauges, radioactive level gauges, etc.

5. Composition analysis instrument:

The composition analyzer is used to verify the composition of the process medium and determine the content of a certain component (or certain components up to all components). According to its working principle, it can be divided into electrochemical analyzer (such as conductivity meter, industrial acidity meter, zirconia analyzer, etc.), thermal analyzer (such as thermal conductivity analyzer, thermochemical analyzer, infrared analyzer) and magnetic analyzer. Conductive analyzers, photoelectric colorimetric analyzers, mass spectrometers, industrial gas chromatographs, etc.

When installing an online component analysis instrument, it is generally necessary to preprocess the sample taken so that the state, temperature, pressure, flow rate and other parameters of the sample meet the requirements of the working conditions of the analysis instrument. Therefore, it is necessary to configure some filters and dust collectors. , Drying container, cooler, rotameter, water seal, valve and pipeline, etc., to perform general pretreatment of the sample.

For some special media (such as flue gas dirty gas samples, furnace gas and other high-temperature gas samples, heavy oil analysis sampling, corrosive component sampling and environmental testing sampling, etc.), the sampling pretreatment system is more complete. This kind of finished product form The sampling pretreatment system is called sampling pretreatment device.

In addition, there are some physical testing instruments such as moisture meters, hygrometers, densitometers, concentration meters, turbidity meters, viscometers, etc., which are often classified as component analysis instruments.

6. Mechanical meter:

The mechanical measuring instruments commonly used in the industry include thickness gauges, thermal expansion detectors, tension detectors, deflection detectors, and shaft vibration, shaft displacement, speed detection devices and scales for rotating machinery (such as large steam turbine compressors, etc.) Heavy equipment (such as electronic belt scale, belt deviation, slip detection device, weighing indicator, weighing bagging device, etc.).

Display instrument

This type of instrument refers to the instantaneous value of the measured parameter that is matched with the detection instrument, such as the ratio meter, millivoltmeter and other moving coil indicator for indicating, digital display instrument and electronic potential for indicating or recording temperature. Difference meter, electronic balance bridge (electronic potentiometer, balance bridge can also be added with electric regulator or pneumatic regulator to form a composite instrument) and cumulative meter with flow accumulation function.

Control instrument

On the one hand, the control instrument accepts the measurement signal of the process detection instrument and the transmitter for display, and on the other hand sends out the adjustment signal to control the action of the actuator (the actuator and the regulating valve), forming a closed-loop control system.

According to the signal type, control instruments can be divided into two categories: analog control instruments and digital control instruments.

1. Analog control instrument

Analog control instruments include base instruments, unit combination instruments (pneumatic, electric) and assembled instruments.

In the development process of industrial automation instruments from on-site detection and display to centralized control, an instrument that integrates measurement, display, and adjustment functions has been produced, which we call base-type adjustment instruments or simply base-type instruments. Such as indicating and recording regulators with pneumatic regulators and some local regulators with only a single regulating function (such as temperature regulators, pressure regulators, differential pressure regulators, flow regulators).

2. Digital control instrument

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

Actuator

Actuator is also called control valve, which consists of two parts: actuator and valve. According to the power source of the actuator, there are four categories: pneumatic control valve, electric control valve, hydraulic control valve and hybrid control valve. Pneumatic control valves are divided into membrane control valves, piston control valves and long stroke control valves according to the form of their actuators.

Centralized monitoring and control device

The centralized detection device is a device that uses detection elements or detectors to centrally display the measured variable or alarm contact signal; the centralized control device is a device that controls a series of measured variable signals according to a set program to control the actuator. Centralized monitoring and control devices include various data acquisition devices, roving detection devices, signal alarm devices, safety detection devices, industrial televisions, remote control devices, and sequence control devices.

Centralized monitoring and control devices are generally divided 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.

2. Industrial TV is composed of cameras and auxiliary equipment (lighting, purging, cooling device and electric turntable), display and auxiliary equipment (operator, distributor, compensator, switcher), etc.

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

4. Signal alarm devices include various types of signal alarm devices such as flash signal alarms, smart flash alarm devices, and relay circuit alarm systems.

5. Sequence control devices include relay interlocking protection system, logic monitoring device, sequence control device and intelligent sequence controller.

6. Data acquisition and patrol detection alarm devices include data acquisition devices and patrol detection alarm devices.

Self-control other equipment

This type of equipment mainly includes various types (channel type, cabinet type, frame type, screen type) instrument panel, instrument box, console, heat preservation (protection) box, power supply box, etc.

Self-control material

Automatic control materials refer to the materials required for instrument installation. There are many varieties, such as pressure guiding pipes (seamless steel pipes, stainless steel pipes, high-pressure pipes), gas supply pipes (galvanized steel pipes, brass pipes), and gas signal pipes (red copper pipes). , Copper tubing, nylon tubing, connecting box), electrical piping materials (welded steel pipes, galvanized steel pipes), valves, flanges and pipe fittings in various piping, electrical equipment materials for automatic control (cables, wires, junction boxes, Electrical equipment and components), instrument cable tray, used to make the angle steel, channel steel and other metal materials of instrument equipment brackets, brackets, heat tracing insulation materials and anti-corrosion oil brushing materials.

Knowledge that automation engineers need to know

Introduction: In industrial applications, temperature is the most involved parameter. Stop heating when the temperature is high, start heating when the temperature is low, or stabilize the temperature at about 100°C. These seemingly simple temperature controls are widely used in industrial applications. The digital display meter is the most economical and reliable product to realize this temperature upper and lower limit control.

Case 1: Temperature alarm control

In industrial applications, temperature is the most involved parameter. Stop heating when the temperature is high, start heating when the temperature is low, or stabilize the temperature at about 100°C. These seemingly simple temperature controls are widely used in industrial applications. The digital display meter is the most economical and reliable product to realize this temperature upper and lower limit control.

There was a technical friend who originally planned to use PLC to monitor the four temperature points on the device. As a result, one set was calculated and found that it was over budget. Later, I asked me if there are any meters directly used for temperature control. After recommending a digital meter to him, the budget was reduced to about one-third, and the temperature control effect achieved was not bad at all. So sometimes, many small things that we ignore can achieve a great effect of four or two shifts. The digital display is a very recommended piece.

Case 2: Temperature record analysis

In industrial situations, real-time monitoring of the entire process of temperature changes is often required. If you send someone to stare at the entire site and record the temperature change process, it takes time and effort. Sometimes the staff is not paying attention and it is easy to remember wrong. Many old technologies generally know that there is a paper temperature recorder, but now that I heard a lot, it has become a paperless recorder.

Paperless recorder

The recorder is an excellent product that saves labor and improves automation in industrial production. Especially in the temperature industry, because the temperature curve can be drawn, temperature data can be exported for a period of time, and the computer can monitor the field temperature parameters in real time, so the recorder has great application prospects in the field of temperature recording and analysis.

The young technology now uses the recorder to record parameters such as pressure, liquid level, PH, etc., and still has good results.

Case 3: Liquid quantitative control

In the field of liquid metering, for production enterprises, there are often requirements for adding water and a certain amount of acid and alkali at one time, and it is best to add the amount of liquid at one time, which can be manually input. This semi-automated method is of great significance to companies like printing and dyeing chemicals.

Not only can the production efficiency be greatly improved with the help of automation, but also the quality of the products produced can also bring great qualitative changes.

Detailed principle analysis

Turbine or electromagnetic flowmeters are often used to detect the flow in the pipeline, followed by a meter with quantitative flow control, or a PLC to read the output signal of the flowmeter. After reaching the set value, the subsequent pumps or valves are automatically stopped.

Case 4: Pressure control start and stop

Pressure control, especially water pressure control, is widely used in the water treatment industry. Here are two cases of constant pressure water supply and hydraulic industry.

1. Frequency conversion constant pressure water supply

In buildings or water supply pipe networks, it is often necessary to keep the pressure constant around a certain value (such as 1.0MPa). At this time, it is often used with a pressure transmitter (for higher requirements) or a remote pressure gauge (with low control accuracy) as an on-site pressure measuring instrument. The pressure signal directly enters the inverter, and the PID control function of the inverter is used to adjust the subsequent pumps or valves to stabilize the pressure value within a certain range.

2. Start and stop of hydraulic equipment

In many pressure control situations, when the pressure reaches a certain pressure, it is required to stop the pressure. Or during the pressure holding test, when the pressure falls below a certain value for a period of time, an alarm is required. At this time, a digital pressure controller that integrates three functions: pressure value display, alarm input, and switch control output is often used.

A digital display pressure controller integrates many functions. In occasions with fewer pressure control points, choosing this small pressure control instrument can reduce a lot of unnecessary wiring troubles and achieve better pressure control effects.

5. Online monitoring of pH

In general pH value detection, in many occasions, special experimental instruments are often used to detect the pH value of the solution. However, sometimes a pot of ingredients is often added with acid and alkali for neutralization. If this is done every time, the workload is very huge, and there are great safety risks.

At this time, an online pH meter is used to monitor the pH value, which can not only monitor in real time, but also set high and low alarms for the pH value. It can also cooperate with PLC to build a set of automatic acid and alkali control system.

However, special attention should be paid to the selection of pH timer, and the temperature change range of the measuring solution must be determined. In addition, due to real-time monitoring, it is usually about one month to maintain the electrode once. Electrodes that have been used for more than half a year should be replaced.

Final summary:

The five categories summarized above are some of the more frequently encountered cases in daily industrial production. I hope to help you.

Complete knowledge of selection of various automation instruments

In the industrial production process, the instrument plays an important role in detecting, displaying, recording or controlling process parameters. The inspection of the technological production process is the basic means to understand and control industrial production. Only by accurately understanding the overall picture of the technological process at any time and controlling it, can the production process be ensured smoothly, and the production can be produced with high productivity and low consumption. qualified products.

So, don't look at the inconspicuous appearance, but it is the most indispensable! Today, the editor will take you to learn the selection of various instruments, which is very comprehensive!

Today, I will introduce the selection of automation instruments, temperature instruments, pressure instruments, flow instruments, and level instruments.

Ⅰ. General principles of automatic instrument selection

The general principles for the selection of detection instruments (components) and control valves are as follows:

1. Process conditions

The temperature, pressure, flow, viscosity, corrosivity, toxicity, pulsation and other factors of the process are the main conditions that determine the selection of the instrument. It is related to the rationality of the instrument selection, the service life of the instrument and the fire prevention, explosion protection and security of the workshop. problem.

2. The importance of operation

The importance of the parameters of each detection point in operation is the basis for the selection of the instrument's instructions, recording, accumulation, alarm, control, and remote control functions. Generally speaking, the variables that have little impact on the process, but the variables that need to be monitored frequently, can be indicated. For important variables that require frequent understanding of the trend, the record type should be selected; and some of the variables that have a greater impact on the process require Variables that can be monitored at any time should be controlled; for variables related to material balance and power consumption that require measurement or economic accounting, it is appropriate to set up totalization; some variables that may affect production or safety should be set to alarm.

3. Economy and unity

The selection of the instrument is also determined by the scale of investment, and the necessary economic calculations should be carried out on the premise of meeting the requirements of process and automatic control to obtain a suitable performance/price ratio.

In order to facilitate the maintenance and management of the instrument, the unity of the instrument should also be paid attention to when selecting the model. Try to choose products of the same series, the same specifications and models, and the same manufacturer.

4. The use and supply of meters

The selected instrument should be a relatively mature product, and its performance has been proven to be reliable by on-site use; at the same time, it should be noted that the selected instrument should have an abundant supply of goods and will not affect the construction progress of the project.

Ⅱ. Selection of temperature instrument

1. General principles

1 unit and scale (scale)

The scale (scale) unit of the temperature meter is uniformly Celsius (℃).

2 Detect (measure) the insertion length of the component

Insertion length selection