Type selection and development trend of the hottes

Type selection and development trend of electric actuator

electric actuator is also called valve electric device, which is the appellation in different industries. It is called valve electric device in industrial pipeline valve industry and electric actuator in instrument industry. But now there is no clear distinction in the industry. The appellation problems involved in this paper will be uniformly called electric actuator

valves are often used as important equipment in industrial pipeline control. With the development of industrial automation, electric valves are more commonly used than pneumatic, hydraulic and other equipment with different driving modes because their power sources are easy to obtain and generally do not need maintenance. In industrial occasions, the electric valve must have higher reliability and safety. When the valve can ensure the performance and service life, the safety and reliability of the electric valve depend on the electric actuator. Therefore, the performance and control level of the electric actuator are the comprehensive performance of the technical level of the whole electric valve. Therefore, in addition to some basic elements that must be considered in the selection of electric actuator, reasonable technical requirements should be put forward to maximize the value of electric valve

there are many types of electric actuators. Electric actuators with different types and functions can be called electric valves after they are matched with valves. However, they often pay attention to the parameters of valves in the process of design and type selection and ignore or do not specify the relevant requirements of electric actuators. This will not only make the electric valves fail to give full play to their best performance, but also bring unnecessary troubles in the process of installation, commissioning and use, Even cause serious consequences to production

this paper will explain the key points considered in the selection of electric actuator, and briefly introduce the relevant functions of the current intelligent electric actuator, which will be the mainstream product for the development of industrial automation control today and even in the future

(I) key points for selection of electric actuator

I. select electric actuator according to the type of valve

there are quite a lot of types of valves, and the working principle is also different. Generally, the opening and closing control is realized by rotating the valve plate angle, lifting the valve plate, etc. when matching with the electric actuator, the electric actuator should first be selected according to the type of valve

1. angular stroke electric actuator (angle 360 °)

the rotation of the output shaft of the electric actuator is more than one cycle, that is, more than 360 degrees. Generally, it takes more than one cycle to realize the opening and closing process control of the valve

this kind of electric actuator is suitable for gate valves, globe valves, etc

3. straight stroke (linear motion)

the motion of the output shaft of the electric actuator is linear motion, not rotation. The hydrostatic forklift of Linde company in Germany has been introduced in China

this kind of electric actuator is suitable for single seat regulating valve, double seat regulating valve, etc

second, determine the control mode of the electric actuator according to the production process control requirements

the control mode of the electric actuator is generally divided into switch type (open-loop control) and regulation type (closed-loop control)

1. switch type (open-loop control)

switch type electric actuator generally realizes the opening or closing control of the valve. The valve is either in the fully open position or in the fully closed position. Such valves do not need to accurately control the medium flow

it is particularly worth mentioning that the switch type electric actuator can also be divided into split structure and integrated structure due to different structural forms. This must be explained during model selection, otherwise mismatches such as conflicts with the control system will often occur during field installation

a) split structure (usually referred to as ordinary type): the control unit is separated from the electric actuator. The electric actuator cannot control the valve alone, and the control unit must be added to realize the control. Generally, the external controller or control cabinet is used for supporting

the disadvantage of this structure is that it is not convenient for the overall installation of the system, increases the wiring and installation costs, and is prone to faults. When faults occur, it is not convenient for diagnosis and maintenance, and the cost performance is not ideal

b) integrated structure (usually referred to as the whole body): the control unit and the electric actuator are encapsulated into a whole, and the local operation can be realized without external control unit, and the remote operation can be carried out only by outputting relevant control information

the advantage of this structure is that it is convenient for the overall installation of the system, reduces the wiring and installation costs, and is easy to diagnose and troubleshoot. However, the traditional integrated structure products also have many imperfections, so the intelligent electric actuator is produced. The intelligent electric actuator will be explained later

2. Regulating type (closed-loop control)

regulating type electric actuator not only has the function of switch type integrated structure, but also can accurately control the valve, so as to accurately adjust the medium flow. Due to the limited space, its working principle is not described in detail here. The following is a brief description of the parameters to be noted when selecting the type of adjustable electric actuator

a) type of control signal (current and voltage)

the control signal of regulating electric actuator generally includes current signal (4 ~ 20mA, 0 ~ 10mA) or voltage signal (0 ~ 5V, 1 ~ 5V). The type and parameters of control signal should be clear during model selection

b) working mode (electric on type, electric off type)

the working mode of regulating electric actuator is generally electric on type (taking 4 ~ 20mA control as an example, electric on type refers to 4mA signal corresponding to valve off, 20mA corresponding to valve on), and the other is electric off type (taking ma control as an example, electric on type refers to 4mA signal corresponding to valve on, 20mA corresponding to valve off). Generally, the type selection needs to clarify the working form. Many products cannot be modified after leaving the factory. The intelligent electric actuator produced by Ogilvy valve control can be modified at any time through on-site setting

c) loss of signal protection

loss of signal protection refers to that when the control signal is lost due to faults such as line, the electric actuator will open and close the control valve to the set protection value. The common protection values are full open, full close and keep in place, which are not easy to modify after delivery. The intelligent electric actuator produced by Ogilvy valve control can be flexibly modified through on-site setting, and any position (0~100%) can be set as the protection value

III. determine the output torque of the electric actuator according to the torque required by the valve

the torque required for the opening and closing of the valve determines the output torque of the electric actuator, which is generally proposed by the user or selected by the valve manufacturer. As an actuator manufacturer, it is only responsible for the output torque of the actuator. The torque required for the normal opening and closing of the valve is determined by the valve caliber, working pressure and other factors, but due to the processing accuracy The assembly process is different, so the torque required for valves of the same specification produced by different manufacturers is also different. Even the torque of valves of the same specification produced by the same valve manufacturer is also different. When selecting the type, the torque selection of the actuator is too small, which will result in the failure to open and close the valve normally. Therefore, the electric actuator must choose a reasonable torque range

IV. determine the electrical parameters according to the selected electric actuator

because the electrical parameters of different actuator manufacturers are different, it is generally necessary to determine the electrical parameters during design and selection, mainly including motor power, rated current, secondary control circuit voltage, etc., which are often neglected in this regard. As a result, the control system does not match the parameters of the electric actuator, resulting in time-space tripping during operation, and the proportion of exports to emerging countries will also be greatly increased Faults such as fuse fusing and thermal overload relay protection jumping

v. select the enclosure protection grade and explosion-proof grade according to the application occasion

1. enclosure protection grade

enclosure protection grade refers to the anti foreign object and water-proof grade of the housing of the electric actuator, which is represented by the letter IP plus two digits. The first digit is 1 ~ 6, indicating the anti foreign object grade (see Table 1), and the second digit is 1 ~ 8, indicating the water-proof grade (see Table 2)

Table 1. The first digit represents the level of foreign object protection

digital protection level

brief description of the meaning of the model

0 no protection. When the protection feature is omitted, there is no special protection

1 protection of solid with a diameter of> 50mm can prevent solid foreign matters with a diameter of more than 50mm from entering the shell, and a large part of the human body, such as the hand (but there is no protection against conscious contact)

2 protection of solid with diameter> 12.5mm can prevent fingers or similar objects, and solid foreign matters with diameter exceeding 12mm and length not exceeding 80mm from entering the shell

3 protection of solid with diameter> 2.5mm can prevent foreign matters such as tools and wires with diameter greater than 2.5mm from entering the shell

4 protection of solids with a diameter greater than 1.0mm can prevent solid foreign matters with a diameter greater than 1mm from entering the shell

5 dust prevention cannot completely prevent dust from entering the shell, but the amount of dust entering is insufficient to hinder the normal operation of the equipment

6 dust dense, no dust entering

Table II. The second digit represents the waterproof grade

digital protection grade

brief description definition

0 no protection. When this protection feature is omitted, there is no special protection

1 anti dripping vertical dripping has no harmful effect

2 when the 15 ° anti dripping equipment forms an angle of 15 ° with the vertical line, the vertical dripping has no harmful effect

3 there is no harmful effect when the anti drenching water is within 60 ° from the vertical line

4 prevent splashing. Splashing in any direction has no harmful effect

5 anti water spray has no harmful effect on flushing in any direction

6 prevent the water entering the shell from reaching harmful effects in case of strong waves or strong water spray

7 prevent immersion. After immersion in water with specified pressure for a specified time, the amount of water entering the shell will not reach harmful effects

8 anti diving can dive for a long time according to the conditions specified by the manufacturer, and its technical conditions are specified by the manufacturer

2. Explosion proof grade

in places where explosive gas, steam, liquid, combustible dust, etc. may cause fire or explosion hazards, it is necessary to put forward explosion-proof requirements for electric actuators, and select explosion-proof forms and categories according to different application areas. The explosion-proof grade can be indicated by the explosion-proof mark ex and the explosion-proof content (refer to explosion-proof electrical equipment for explosive atmospheres GB3836-2000)

the contents of explosion-proof signs include: explosion-proof type + equipment category + (gas group) + temperature group

A) explosion proof type: according to the explosion-proof measures taken, it can be divided into intrinsically safe type, explosion-proof type, increased safety type, positive pressure type, pouring sealing type, sand filling type, etc. Their identification is shown in Table 3 below.

Table III. explosion proof form and mark

explosion proof type explosion proof type mark explosion proof type explosion proof type mark

intrinsically safe exi flameproof Exd

sand filled e x Q increased safety exe

encapsulated e x m positive pressure exp

b) equipment category:

Table IV. equipment category

class I underground coal mine electrical equipment.

class II electrical equipment for explosive gas atmospheres other than coal mines

class II flameproof "Exd" and intrinsically safe "exi" electrical equipment are further divided into IIA, IIB, and IIC according to their maximum test safety gap or minimum ignition current ratio applicable to explosive gas mixtures. The relationship between others is shown in Table 5:

table 5 Gas group

Gas Group maximum test safety gap MESG (mm) minimum ignition current ratio MICR

IIA MESG ≥ 0.9 MICR> 0.8

IIB 0.9> MESG> 0.5 0.8 ≥ MICR ≥ 0.45

IIC 0.5 ≥ MESG 0.45> MICR

C) temperature category:

electrical equipment according to its highest surface