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Selection of electric actuators and development trends
2009-5-9

Electric valve actuators, also known as electric devices, it is in different areas of the title industry, valve industry in the industrial pipeline valves known as the electric device, known as the electric industry in the implementation of instruments, but now the industry has no clear distinction, this article relates to the issue on the title will be called a unified electrical actuators.
 
     Control valves in industrial piping is frequently used in critical equipment, electric valve with the development of industrial automation, easier access to its power source, and under normal circumstances the advantages of maintenance than pneumatic, hydraulic and other drive more widespread use of the equipment. Occasions in the industrial electric valve must have higher reliability and security, when the valve to ensure the performance and life circumstances, the electric valve depends on the security and reliability of electric actuators, electric actuators, therefore the performance of , control valves electric machine technology is the overall performance level. Therefore, when the electric actuator selection must be considered in addition to some basic elements, its reasonable to make the technical requirements for maximizing the value of electric valves.
 
     The type of electric actuators are many different types and functions of the electric valve actuators and can be called after matching electric valves, but often in the design, selection of only the importance of the process parameters of the valve electric ignored or not clearly Actuator requirements, so not only can not play electric valves the best performance, but also in the installation, commissioning, use the process will cause unnecessary trouble, and even to produce serious consequences.
 
     This electric actuator for the Selection of points to consider that the current implementation of intelligent electrical devices related functions do so briefly, it is in today's industrial automation control and the future development of mainstream products.
 
     (A) Electric Actuator Selection considerations
 
     First, according to the type of choice of electric valve actuators
 
A considerable number of types of valves, is not the same working principle, the general point of view in order to rotate the valve, the valve lift, etc. to achieve the hoist control, when the electric actuator with the first matching should be based on the type of choice of electric valve actuators .
 
1. Travel electric actuator angle (angle <360 degrees)
 
     Electric actuator output shaft rotation is less than a week, that is, less than 360 degrees, 90 degrees is usually a gate valve on the realization of process control. Such electric actuators in accordance with the different interface mode installation is divided into direct style, crank-type base two.
 
     a) Direct Connect: is the electric actuator output shaft and the stem form of Direct Connect is installed.
 
     b) crank-type base: refers to the output shaft connected through the crank and stem form.
 
     Such electric actuators for butterfly valves, ball valves, plug valves and so on.
 
     2. Multi-turn electric actuator (angle> 360 degrees)
 
     Electric actuator output shaft rotation is greater than a week, that is, greater than 360 degrees, it generally takes more than can be achieved loop process control valve of the headstock.
 
     Type of electric actuator for valve, such as cut-off valve.
 
     3. Straight trip (linear motion)
 
     Electric actuator output shaft to linear motion of the campaign-style, not the form of rotation.
 
     Such electric actuators for single-seat control valve, control valve, such as two-seater.
 
   
     Second, according to production process control requirements for electric actuators to determine the control mode
 
     Electrical actuators are generally divided into the control mode switching-type (open-loop control) and regulation of type (closed-loop control) two broad categories.
 
     1. Switch-type (open-loop control)
 
     Switch electric actuators for valves in general to achieve the control on or off, or in a full-position valves, or related position in the whole of such valves do not need to accurately control the flow medium.
 
     Particularly worth mentioning is the switch from electric actuator structure can be divided into different forms of structure and integration of sub-structure. Selection of the need to make note of this, otherwise often occur at the scene and control system installed does not match the conflict is like.
 
     a) sub-structure (often referred to as the general type): the control unit and the separation of electric actuators, electric actuators can not achieve control of the valve, plus a control unit necessary to achieve control, the use of the general external form of controller or control cabinet for matching.
 
     The shortcomings of this structure is not easy to install the system as a whole, increasing the cost of wiring and installation, and prone to failure, when failure is not easy at the time of diagnosis and maintenance, cost-effective is not ideal.
 
     b) the integration of structure (often referred to as the overall type): the control unit and electric actuator packages into one, with no external control unit can be a reality in situ operation, remote control only the output information can be related to their operation.
 
     The advantages of this structure is to facilitate the installation of the system, reducing wiring and installation costs, easier diagnosis and troubleshooting. However, the integration of traditional structured products have a lot of imperfections, so have had a smart electric actuators, electric actuators on the back of the smart will do that.
 
     2. Regulation of type (closed-loop control)
 
     Regulation of electric actuator with a switch not only the integration of structure-based function, it can carry out precise control of valves in order to accurately regulate the flow medium. Due to the limited length of the principle of its work do not give a more detailed explanation. The following regulation on the selection of electric actuators indicate when a brief description of the parameters.
 
a) control signal type (current, voltage)
 
     Regulation of electric actuator control signals generally have current signal (4 ~ 20mA, 0 ~ 10mA) or voltage signal (0 ~ 5V, 1 ~ 5V), selection of control when a clear signal of its type and parameters.
 
     b) the work of the form (open-type electric, electricity-off)
 
     Regulation of electric actuators for electrical work normally open type (for 4 ~ 20mA control as an example, electricity is the type to open the corresponding signal is 4mA valve clearance, 20mA corresponds to the valve open), and the other for the power-off (to 4-20mA control as an example, electricity is the type to open the corresponding signal is 4mA valve open, 20mA correspond to valve clearance). Selection generally takes the form of a clear, after a lot of products in the factory and can not be modified, Ogilvy & Mather produced intelligent valve electric actuator can be amended at any time through on-site settings.
 
     c) signal loss protection
 
     Loss of signal protection means, such as fault lines caused by the loss of control signal, the electric actuator gate valve will be controlled to set the protection of values, common values for the full protection of all clearance and maintain the three conditions in situ, After the factory and not easy to modify. Ogilvy & Mather produced intelligent electric valve actuator can be set flexibly through on-site modifications, and set at any position (0 ~ 100%) for the protection of value.
 
    
     Third, according to the required valve torque electric actuator to determine the output torque
 
     Gate valve torque required to determine the choice of how much electric actuator output torque is generally made by the users or the manufacturers using their own matching valve, actuator manufacturers for the implementation of only the output torque is responsible for, the normal valve Kai torque required to close by the valve diameter size, work pressure and other factors, but the valve manufacturers machining accuracy, the assembly process be different, so different manufacturers with the specifications of valve torque requirements are also different, even with the manufacturers valves with valve torque specifications have differences, election-type actuator when the torque is too small will result in selection can not hoist valves, electric actuators, therefore necessary to choose a reasonable range torque.
 
     Fourth, in accordance with the implementation of the selected electrical device to determine electrical parameters
 
Actuators due to different manufacturers vary the electrical parameters, so the design is generally required when the selection to determine their electrical parameters, mainly electric power, rated current, secondary voltage control loop, are often negligent in this respect, the results of control system electrical parameters and the implementation of the work does not match the space-time caused by tripping open, fuse fuse, thermal overload relay protection is like a take-off, such as failure.
 
     Fifth, use the occasion to choose in accordance with shell protection grade, explosion-proof rating
 
     1. Shell protection grade
 
     Protective shell is the level of the shell of electric actuator anti-foreign objects, water levels in order to double-digit after the letters IP said that the first 1 ~ 6 expressed by the anti-foreign object hierarchy (see Table 1), second place from 1 to 8 that the water level (see Table II).
 
Table I, the first figures represent the level of anti-foreign objects

Table II, the second-digit level on behalf of the waterproof
 
2. Explosion-proof rating
 
     May occur in explosive gas, steam, liquids, combustible dust, such as fire or explosion arising from dangerous places, the essential of the explosion-proof electric actuators to the requirements of the application of different forms of regional options and types of explosion-proof. Explosion-proof grade through EX explosion-proof and explosion-proof signs to indicate the content (refer to "the explosive use of explosion-proof electrical equipment environment" GB3836-2000).
 
     Explosion-proof signs include: types of explosion-proof type + equipment + (gas group) + temperature groups
 
a) Explosion-proof type: According to the measures taken by the explosion-proof, can be divided into the intrinsic safety type, Flameproof, Increased Safety, pressure type, water seal type, such as filling sand. Their logo in the following table III. 
 
     Table III sign the form and explosion-proof

b) Equipment Type:
 
     Table IV equipment categories

     Class II Flameproof "Exd" and intrinsically safe type "Exi" according to their electrical equipment for explosive gas mixtures of the biggest security gaps or minimum test current ratio lighting, and further divided into further divided into IIA, IIB, and IIC type, other the relationship between the following Table V:
 
     Table V, the gas group

     c) temperature categories:
 
     Electrical equipment according to the maximum surface temperature T1 ~ T6 group into which the corresponding T1 ~ T6 group of electrical equipment can not exceed the maximum surface temperature of the temperature of the corresponding value of group's permission. Temperature groups, equipment, surface temperature and flammable gases or vapors ignite the relationship between temperature in the following table VI:
 
     Table 6, the temperature groups

 


(B) Intelligent electric actuator is the mainstream of development and future
 
     Consider the five factors mentioned above the basic electric actuator can be a good selection, but with the continuous development of industrial automation, in particular the rapid development of computer speeds, the traditional drawbacks of electric actuator functions can not be achieved and also show us their sense of , a safe, stable, reliable, user-friendly, intelligent electric actuators and control systems to adapt. Intelligent electric actuator so what are the advantages of it? It can help solve the drawbacks of traditional products which do? Below 380V for electric power-driven smart actuator briefly the advantages of doing.
 
     A wealth of information display and user-friendly interface of man-machine dialogue
 
     Traditional electric actuators in general do not have too many messages, so it is difficult to know at the scene of the operation of electric valves, especially when there is not easy to fault diagnosis and troubleshooting. Intelligent electric actuators solved the problem, he would run the electric actuator to detect and display information through the LCD screen, so that to reduce a lot of man-made diagnosis and troubleshooting in time to resume production. Particularly worth mentioning is that many product code or English is often not easy to understand the operation of the field, the real man-machine dialogue human interface should be in full-text display, Ogilvy & Mather intelligent production of electric valve actuator is in full-text menu display.
 
     Second, the multi-configurable signal output
 
     Electric actuator is the number of signal output actuators and valves for their own surveillance operation, one embodiment of the magnitude of the problem, the traditional electric actuator is the general machinery output contact micro-switches, the output points is limited, and a fixed form and information on the definition of fixed output, such as in the selection did not explicitly request, but the product of a factory it is very difficult to change, so flexibility is not easy-to-use and powerful control system can not meet the requirements. Intelligent electric actuators necessary to have more points of the signal output and the corresponding configuration information can be flexibly defined.
 
     Third, to resolve the issue of phase sequence
 
     Three-phase motor phase sequence there is a problem, when the three-phase power supply phase sequence error, open the control valve, valve clearance and valve when the actual turning the other hand, will result in out-of-control electric actuators, valve damage. Therefore, when necessary for the initial installation phase sequence correcting manually, otherwise the damage would be inevitable, but often at the scene is different debug connection with staff, often there is no phase sequence error correction of the damaged equipment is like. And intelligent electric actuators do not have to consider the issue of phase sequence, internal access to AC power detection circuit of the phase sequence, through the automatic error correction logic operations, regardless of how then can the work of the right turn.
 
But the lack of three-phase motor with a motor will be damaged, the traditional electric actuator does not have the general lack of protection. Intelligent electric actuator for detection of three-phase power supply, lack of phase in a timely manner to protect the time. Need to pay attention to the fact that the vast majority of the motor phase is missing when the motor is running, and the general lack of detection can only detect the lack of electric static phase. Ogilvy & Mather produced intelligent electric valve actuators in the dynamic and static under the lack of real-time detection of the existence of a similar occurrence of the vacancy will be timely protection, through the screen display, the issue of alarm signal.
 
     Fifth, super self-diagnosis function
 
     Actuator run regardless of electric or not, but was connected to a power on self-diagnostic tests necessary, when the failure diagnosis of the operation will be prohibited, and liquid crystal display showing the fault alarm information, and signal output to the control system , so that the equipment is safe, reliable not only add another layer of insurance, but also shorten the troubleshooting time, so that the realization of intelligent fault diagnosis, this is not traditional features.
 
     Six to modify the parameter settings
 
     Traditional electric actuator, after the general parameters of the factory can not be changed, intelligent electric actuator changed this limitation, it is set to achieve through internal procedures, parameters can be modified at any time, whether it is the beginning of the process of loading or the use of all can be modified so that equipment to play its powerful flexibility.
 
     7, non-invasive isolation seal
 
     Traditional electric field operation of the actuator button (or knob) axis generally used to pass, so poor sealing performance, intelligent electric actuators generally use non-intrusive design, operation buttons and the complete separation of the internal circuit, the sealing problem is completely resolved . Openings set to achieve a free, operation, query.
 
 

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