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Yangzhou Kaidesi Environmental Protection Equipment Co., Ltd. specializes in the development of electric valves and electric actuators

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How to choose the electric actuator (electric actuator) model

发表时间:2019-01-15 12:38:14 Article source: Publication time: 2019-01-15 12:38:14

Electric actuator is also called valve electric device or electric head. It is the title in different industries. It is called valve electric device in the industrial pipeline valve industry and electric actuator (electric actuator) in the instrument industry.

Valves are very important equipment often used in industrial pipeline control. Electric valves are easier to obtain due to their power source, and generally require no maintenance. They are more commonly used than pneumatic, hydraulic and other driving methods. In industrial occasions, electric valves require higher reliability and safety. The safety and reliability of electric valves usually depend on electric actuators (electric actuators), so the performance, control accuracy, function, The intelligent program is the comprehensive expression 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 actuators (electric actuators), reasonable technical requirements are required to maximize the value of electric valves.

There are many types of electric actuators (electric actuators). Different types and functions of electric actuators (electric actuators) can be called electric valves when they are matched with valves, but they are often only valued during the design and selection process. Parameters and neglecting or not clarifying the relevant requirements of electric actuators (electric actuators). This will not only make the electric valve not perform optimally, but also cause unnecessary trouble during installation, commissioning and use. It even has serious consequences for production.

This article will explain the main points of consideration for the selection of electric actuators (electric actuators), and briefly introduce the related functions of current intelligent electric actuators (electric actuators).

(I) Points for consideration in the selection of electric actuators (electric actuators)

I. Selecting electric actuators (electric actuators) according to the type of valve

There are many types of valves, and the working principles are not the same. Generally, the opening and closing control is achieved by rotating the valve plate angle, lifting the valve plate (or valve core), etc. When it is matched with an electric actuator (electric actuator) Select the electric actuator (electric actuator) according to the type of valve.

1.Angle stroke electric actuator (electric actuator) (rotation angle <360 degrees)

The rotation of the output shaft of the electric actuator (electric actuator) is less than one round, that is, less than 360 degrees (sometimes called the angle and other strokes within 90 degrees, and greater than 90 degrees and less than 360 degrees is called partial rotation type), usually 90 degrees to achieve the valve Opening and closing process control. This type of electric actuator is divided into direct connection type and base crank type according to different installation interface methods ("Selection Methods and Techniques of Electric Actuators" are explained in more detail).

a) Direct connection type: refers to the form in which the output shaft of the electric actuator (electric actuator) is directly connected to the valve stem.

b) Base crank: refers to the form in which the output shaft is connected to the valve stem through a crank.

This type of electric actuator is suitable for butterfly valves, ball valves, plug valves, etc.

2.Multi-turn electric actuator (electric actuator) (rotation angle> 360 degrees)

The rotation of the output shaft of the electric actuator is more than one turn, that is, more than 360 degrees, and it usually takes multiple turns to achieve the valve opening and closing process control.

This type of electric actuator is suitable for gate valves, globe valves, etc.

3.Straight stroke (linear motion)

The movement of the output shaft of the electric actuator (electric actuator) is a linear movement type, not a rotating form.

This type of electric actuator is suitable for single seat regulating valve, double seat regulating valve, etc.

2. Determine the control mode of the electric actuator (electric actuator) according to the production process control requirements

The control mode of the electric actuator (electric actuator) is generally divided into two types: switch type (open loop control) and regulation type (closed loop control, that is, a servo amplifier with built-in PID adjustment function).

1. Switch type (open loop control)

Switch-type electric actuators (electric actuators) generally realize the opening or closing control of the valve. The valve is either in the fully open position or the fully closed position. Such valves do not require precise control of the medium flow rate (this is not complete here) There is also a switch type with valve position feedback. The feedback signal is connected to DCS or other controllers for PID calculation and then controls the actuator to open or close to achieve the purpose of controlling the opening degree).

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

a) Split structure (commonly referred to as common type): The control unit is separated from the electric actuator. The electric actuator cannot control the valve alone. The control unit must be added to achieve the control. Generally, the controller or control cabinet is used externally. Supporting.

The disadvantages of this structure are that it is not convenient for the overall installation of the system, increases wiring and installation costs, and is prone to failure. It is not easy to diagnose and repair when a failure occurs, and the cost performance is not ideal (but the advantage is that it is suitable for high temperature situations, because the control circuit can be far away from the actuator High temperature environment).

b) Integrated structure (usually called integral type): The control unit and the electric actuator are packaged into a single body, which can be operated on the spot without external control units, and can be operated remotely by simply outputting relevant control information.

The advantage of this structure is that it facilitates the overall installation of the system, reduces wiring and installation costs, and facilitates diagnosis and troubleshooting. However, there are also many imperfections in the traditional integrated structure products (the traditional analog control circuit mentioned here), so intelligent electric actuators have been produced. The intelligent electric actuators will be described later.

2.Adjustable (closed-loop control) (i.e. servo integration)

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

a) Control signal type (current, voltage)

The control signals of adjustable electric actuators (electric actuators) are generally current signals (4-20mA, 0-10mA) or voltage signals (0-5V, 1-5V). When selecting the type, the control signal type and parameters ( 4 to 20 mA is currently the most commonly used).

b) Working form (electric on type, electric off type) (i.e. positive action and negative action)

Regulating electric actuators (electric actuators) generally work in the electric open type (take 4-20mA control as an example, the electric open type means that the 4mA signal corresponds to the valve close, and 20mA corresponds to the valve open), and the other The type is an electric close type (take 4-20mA control as an example, the electric open type means that the 4mA signal corresponds to the valve open and 20mA corresponds to the valve close). In general, the selection of the type requires a clear working form. Many products cannot be modified after leaving the factory (should be some products). Most intelligent electric actuators (such as CONAC series, NDL, NDQ series) can be modified at any time through field settings ( If you modify the parameter or jumper, the traditional analog control board has to change the jumper, or you must change the motor's forward and reverse wiring and sensor wiring).

c) Lost signal protection

Lost signal protection means that when the control signal is lost due to a fault such as a line, the electric actuator (electric actuator) opens and closes the control valve to a set protection value. The common protection values are fully open, fully closed, and held in place. In this case, and it is not easy to modify after leaving the factory (it should be difficult to modify the old-fashioned analog control form), most of the intelligent electric actuators can be flexibly modified through field settings, such as CONAC series, NDL, NDQ series, etc. can be modified by menu parameters To achieve, the NDL and NDQ series can set the valve position to any set position when the break signal is set.

3. Determine the output torque of the electric actuator (electric actuator) according to the torque required by the valve (thrust can be input)

The torque required for valve opening and closing determines how much output torque the electric actuator (electric actuator) chooses. Generally, it is proposed by the user or selected by the valve manufacturer. As an electric actuator (electric actuator), the manufacturer only applies the actuator. The output torque is responsible for the valve. The torque required for the normal opening and closing of the valve is determined by the valve diameter and working pressure. The difference is that even the torque of the valve of the same specification produced by the same valve manufacturer is different. When the torque of the electric actuator (electric actuator) is selected too small, the valve cannot be opened and closed normally, so an electric actuator must choose one. Reasonable torque range. (The article "Selection Methods and Techniques of Electric Actuators" has a more detailed explanation)

Fourth, determine the electrical parameters

Because the electrical parameters of different electric actuator (electric actuator) manufacturers are different, the electrical parameters generally need to be determined when designing and selecting, mainly including motor power, rated current, secondary control loop voltage, etc., often in this regard Negligence, as a result, the mismatch between the parameters of the control system and the electric actuator caused faults such as air-open tripping, fuse blowing, and thermal overload relay protection tripping during work.

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