Introduction to Selection of Electric actuators (2)
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2016-03-22
2、 Determine the control mode of the electric actuator according to the production process control requirements The control modes of electric actuators are generally divided into two categories: switch type (open loop control) and adjustment type (closed-loop control). 1. Switch type (open loop control) Switch type electric actuators generally achieve open or close control of valves. The valves are either in the fully open or fully closed position, and this type of valve does not require precise control of medium flow.
It is particularly worth mentioning that switch type electric actuators can be divided into split structure and integrated structure due to different structural forms. When selecting a model, it is necessary to explain this, otherwise mismatches such as conflicts with the control system during on-site installation may often occur.
1) Split structure (usually referred to as ordinary type): The control unit is separated from the electric actuator, and the electric actuator cannot independently control the valve. It is necessary to add a control unit to achieve control. Generally, the external system is equipped with a controller or control cabinet.
The disadvantage of this structure is that it is not convenient for the overall installation of the system, increases wiring and installation costs, and is prone to faults. When faults occur, it is not easy to diagnose and repair, and the cost-effectiveness is not ideal.
2) Integrated structure (usually referred to as whole body): The control unit and electric actuator are packaged into one unit, and can be operated locally without the need for an external control unit. Remote operation can only be carried out by 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 is easy to diagnose and troubleshoot. However, traditional integrated structural products also have many imperfections, resulting in the emergence of intelligent electric actuators. We will explain the intelligent electric actuators later. 2. Regulating type (closed-loop control) The adjustable electric actuator not only has the function of an integrated switch structure, but also can accurately control the valve and adjust the medium flow rate. Due to limited space, its working principle will not be explained in detail here. Below is a brief explanation of the parameters that need to be noted when selecting adjustable electric actuators.
1) Control signal type (current, voltage)
The control signals of regulating electric actuators generally include current signals (4-20mA, 0-10mA) or voltage signals (0-5V, 1-5V). When selecting, it is necessary to clarify the type and parameters of the control signal.
2) Working form (electric on type, electric off type)
The working mode of regulating electric actuators is generally electric on type (taking 4-20mA control as an example, electric on type refers to the 4mA signal corresponding to valve closed and 20mA corresponding to valve open), and the other type is electric off type (taking 4-20mA control as an example, electric on type refers to the 4mA signal corresponding to valve open and 20mA corresponding to valve closed). In general, the selection requires a clear working form, and many products cannot be modified after leaving the factory. The intelligent electric actuators produced can be modified at any time through on-site settings.
3) Loss of signal protection Loss of signal protection refers to the electric actuator that opens and closes the control valve to the set protection value when the control signal is lost due to circuit faults or other reasons. The common protection values are fully open, fully closed, and kept in place, and are not easily modified after leaving the factory. The intelligent electric actuators produced by Aomei Valve Control can be flexibly modified through on-site settings, and can be set to any position (0-100%) as a protection value.
