What Is an Electric Solenoid Actuator?

The broadest definition of an actuator is: a driving device that can provide linear or rotary motion, which uses a certain driving energy and works under a certain control signal. The actuator uses liquid, gas, electricity or other energy sources and converts it into a driving action through a motor, cylinder or other device. Its basic types include three drive methods: Part-Turn, Multi-Turn, and Linear.

The basic actuator is used to drive the valve to the fully open or fully closed position. Used for

In order to successfully automate the process, the most important thing is to ensure that the valve itself can

The main advantages of electric actuators are high stability and constant thrust that can be applied by the user. The maximum actuator can generate thrust of up to 225000kgf. Only hydraulic actuators can achieve such a large thrust, but the cost of hydraulic actuators is higher than electric actuators Much higher.

The anti-deviation ability of the electric actuator is very good. The output thrust or torque is basically constant. It can overcome the unbalanced force of the medium and achieve accurate control of the process parameters. Therefore, the control accuracy is better than that of the pneumatic actuator. high. If equipped with a servo amplifier, it is easy to realize the exchange of positive and negative effects, and it is also easy to set the break signal valve position state (hold / full open / full close), and when it fails, it must stay in place. This is Pneumatic actuators can't do it. Pneumatic actuators must be secured with the help of a combined protection system ^[1]

There are two types of electric actuators, which are generally divided into Part-Turn Electric Valve Actuator and Multi-Turn Electric Valve Actuator. The former mainly controls valves that require partial rotation. For example: Ball valves, butterfly valves, etc., which require valves with multiple revolutions, such as gate valves.

Electric-driven multi-turn actuators are one of the most commonly used and most reliable actuator types. Use a single-phase or three-phase motor to drive gears or worm gears to drive the stem nut last. The stem nut moves the stem to open or close the valve. Multi-turn electric actuators can quickly drive large size valves. In order to protect the valve from damage, the limit switch installed at the end of the valve stroke will cut off the power of the motor. At the same time, when the safe torque is exceeded, the torque sensing device will also cut off the power of the motor. The clutch-equipped handwheel mechanism can manually operate the valve in the event of a power failure.

The main advantage of this type of actuator is that all components are housed in a single housing. All basic and advanced functions are integrated in this waterproof, dustproof and explosion-proof enclosure. The main disadvantage is that when the power fails, the valve can only be kept in place. Only by using a backup power system can the valve achieve a fail-safe position (fault on or fault off).

This type of actuator is similar to an electric multi-turn actuator, the main difference is that the final output of the actuator is a movement of 90 degrees at 1/4 revolution. The new generation of electric single-turn actuators combines most of the complex functions of multi-turn actuators, such as using a non-entering user-friendly interface to set parameters and diagnose functions. Single-turn actuators have a compact structure and can be installed on small-sized valves, usually with an output torque of 800 kgm. In addition, they should have a small power supply. They can be installed with batteries to achieve fail-safe operation.

Take the MD proportional electric actuator as an example.

The MD series electric actuator uses an AC servo motor as the drive mechanism of the position servo. The matched position locator PM-2 control board receives the 4-20mA DC control signal of the adjustment system and the position feedback of the position transmitter. After comparison, the compared signal deviation is amplified to make the power stage conductive, and the output of the actuator is driven by the motor to move in the direction of reducing this deviation (the position transmitter continuously converts the actual position of the output into an electrical signal-bit Feedback signal to the positioner) until the deviation signal is less than the set value. At this time, the output of the actuator is stabilized at the position corresponding to the input signal.

MD series electric actuators for angular stroke adjustment are composed of power parts and position locator (PM-2 control board). The power components are mainly composed of motor, reducer, torque stroke limiter, switch control box, hand wheel and mechanical limit device, and position transmitter. The functions of each part are briefly described as follows:

1.Motor

The motor is a special single-phase or three-phase AC asynchronous motor with high starting torque, low starting current and small moment of inertia, so it has good servo characteristics. The motor stator is equipped with a thermal switch (see Figure 3 for details) to protect it from overheating. When the motor overheats (the internal temperature exceeds 130 ° C), the switch will open the circuit that controls the motor to protect the motor and the actuator When the switch is turned on after the motor has cooled, the circuit resumes operation. In order to overcome the inertia, the motor control circuit of the adjustable electric actuator has an electric braking function.

The operator can use the built-in data memory to record the data measured by the torque sensing device each time the valve is actuated. These data can be used to monitor the valve's operating status, can prompt the valve whether it needs maintenance, and can use these data to diagnose the valve.

The following data can be diagnosed for the valve:

1. Valve sealing or packing friction

2.Friction moment of valve stem and valve bearing

3. Valve seat friction

4. Friction during valve operation

5. Dynamic force on the spool

6. Valve stem thread friction

7.Stem position

Most of the above data exist in all types of valves, but the emphasis is different. For example, for butterfly valves, the frictional force during valve operation can be ignored, but for plug valves, this force value is very large. Different valves have different torque operating curves. For example, for wedge gates, the opening and closing torques are very large. During other strokes, only the packing friction and thread friction are applied. When closed, the hydrostatic pressure increases on the gate. Because of the friction of the valve seat, the final wedging effect rapidly increases the torque until it is closed in place. Therefore, according to the change of the torque curve, the faults that will occur can be predicted, and it can provide valuable information for predictive maintenance.

Take the MD proportional electric actuator as an example.

Before power-on, the appearance inspection and insulation inspection must be performed. The insulation of the power circuit (arc circuit) and signal contacts to the shell must be measured with a 500V megohmmeter at least 20M: signal input, output circuit, and their power Except for special requirements, the insulation between the circuits should not be lower than l0m before passing power. After the power is turned on, check whether the transformer, motor, and some components of the electronic circuit are overheated, and whether there are noises in the rotating parts. If any abnormal phenomenon is found, immediately cut off the power and find out the cause. Do not solder components easily until the cause is identified. When replacing electronic components, prevent excessive temperature and damage to the components. When replacing the field effect tube and integrated circuit, the electric soldering iron must be properly grounded, or the power can be used for welding without the power. When disassembling parts, components, or soldered wires, they should be marked with corresponding marks. Every effort should be made to avoid the output circuit of the equipment under test being open and to prevent power failure of the equipment under test when there is an input signal. The overhauled equipment must be calibrated. For dry motors, check the insulation resistance between the coil and the shell and between the coils, measure the DC coil of the dish coil, clean the bearings and add high-quality lubricants, check the rotor, stator coils and brakes; For the condition of the planetary gear part, check the condition of the helical gear part, check the meshing condition of the turbine scroll or screw nut, and finally perform assembly, adjustment, and extension of the long-acting base grease. For the position sensor part, visual inspection is performed, the coaxial connection of the potentiometer and the stroke control mechanism is checked, the basic condition of the potentiometer is checked, and the connection between the potentiometer and the amplifier board is checked.

Take production safety in various emergencies as an example.

In large-scale pipe network systems, the valves are widely distributed or far away. In order to ensure production safety in various unexpected situations, the valve needs to have the door closed manually after the local power is cut off, and it can also be displayed on site and remotely. The function of monitoring the valve opening degree requires that the electric actuator has a battery-powered low-power manual mode, and enters the manual mode in the event of a local power failure. Using the battery provided can not only display the valve opening degree at the same time, but also It can provide remote valve opening display to play the role of remote monitoring.

Low-power manual mode, which involves low-power LCD screen technology, low-power CPU technology, low-power data acquisition, calculation, processing and transmission, and low-power battery-powered technology. The key is that the valve opening sensor needs to be selected. Full-stroke absolute multiturn encoder. In fact, in the case of manual mode, because the change response is not high, the MCU (microprocessor) can adopt the low-power gap mode, that is, the semi-sleep mode. This can ensure that the power consumption is extremely low, and the battery is provided. The capacity can be used for a longer period of time.

When the function of low power consumption half-sleep mode is selected, the valve opening sensor must be a sensor that does not affect the position memory in the event of a power failure, such as a potentiometer or a full-stroke multi-turn absolute encoder. The accuracy and measurement stroke of the potentiometer are limited. There are two methods for using it on electric actuators. One is to use a potentiometer stroke for one stroke (through variable speed), and the power-off position will not be lost, but that accuracy is very low; One is to use multiple potentiometer strokes, the position accuracy is improved, but each time the stroke is exceeded, it is achieved by electronic memory. When the power is lost, there is no electronic memory position. If the battery is used to realize the memory, it will consume more battery energy. . If the Hall pulse counting method is used, the counting is uninterrupted in real time. After power failure, the battery power consumption is used to memorize, and the battery capacity is insufficient. The full stroke multi-turn absolute encoder is the most likely valve opening sensor to be implemented in this mode. Of course, because the data read time is very short and the accuracy of the data is required, the data reliability requirements of this encoder are required. Very high. Some of the selected absolute encoders are single-turn function. The electronic lap memory is needed to exceed the single-turn. The power consumption of the lap memory after power-off is large, which is not suitable for this semi-sleeping low power consumption mode. .

The full-stroke multi-turn absolute value encoder uses RS485 active mode to send data. The encoder sends data every 8 mS. The encoder's power-on startup time is extremely short. The data includes two verification methods, which has high reliability. The value encoder is uniquely coded at each position in the total stroke and has nothing to do with the previous reading without counting, lap counting and memory, so it can use the gap-type power-on, reading mode, such as every 1-5 seconds , MCU motherboard works intermittently once (or twice), each working time is only tens of milliseconds, and quickly realizes the work of startup, data reading, processing, and sending, and the rest of the time is in the sleep state, which is "half sleep low power consumption" Mode " ^[2]

Take the MD proportional electric actuator as an example.

1.Position sensor section

(1) After the electric actuator receives the on and off signals from the control system, the motor can rotate normally, but there is no valve position feedback. The possible reasons are:

1) The potentiometer of the position sensor and the stroke control mechanism cannot rotate coaxially, and it is necessary to check whether the connecting part is damaged;

2) The potentiometer is damaged or its performance deteriorates, and the resistance value does not change with rotation;

3) Whether the connecting wire between the potentiometer of the position sensor and the amplifier board is normal;

4) Whether the PM amplifier board is damaged and whether there is feedback signal sent out.

(2) After the electric actuator receives the on and off signals from the control system, the motor can rotate normally, but the valve position feedback is always a fixed value and does not change with the opening and closing of the valve. The possible reasons are:

1) The resistance value of the conductive plastic potentiometer is a constant value and does not change with rotation. Repair and replace the potentiometer;

2) The relevant part of the amplification board is abnormal, check and deal with it.

2.Actuator

After the actuator receives the switching signal from the control system, the motor does not rotate and there is a buzzing sound. The reasons may be:

1) The planetary gear part of the reducer is stuck, damaged or deformed;

2) The helical gear transmission of the reducer is deformed or excessively worn or damaged;

3) The turbine vortex rod or screw rod nut transmission part of the reducer is deformed, damaged, jammed, etc .;

4) The overall mechanical part is not well coordinated and inflexible, and adjustment and refueling are required.

Traditionally, cylinders and electric actuators have always been considered as automation products that belong to two completely different fields. With the continuous improvement of the degree of electrification, electric actuators have slowly immersed themselves in the field of pneumatics. Competition complements each other. In this column, we will compare the respective advantages of cylinders and electric actuators in terms of technical performance, purchase and application costs, energy efficiency, application occasions, and market situation.

1. Comparison of technical performance

As we all know, compared with electric actuators, the cylinder can work reliably under harsh conditions, and the operation is simple, which can basically achieve maintenance-free. The cylinder is good at reciprocating linear motion, and is especially suitable for the most demanding conveyance in industrial automation-linear handling of workpieces. Moreover, simply adjusting the one-way throttle valve installed on both sides of the cylinder can simply achieve stable speed control, which also becomes the biggest feature and advantage of the cylinder drive system. Therefore, for users who do not have multi-point positioning requirements, most of them prefer to use cylinders from the perspective of convenience. Most industrial applications using electric actuators require high-precision multi-point positioning. This is because it is difficult to achieve with cylinders. Second best result.
The electric actuator is mainly used in rotating and swinging conditions. Its advantage is that the response time is fast, and the speed, position and torque are accurately controlled by the feedback system. However, when the linear motion needs to be completed, the transmission conversion needs to be performed by mechanical devices such as toothed belts or screw rods, so the structure is relatively complicated, and the working environment and the professional knowledge of operation and maintenance personnel have high requirements.

1. Input signal: 220V AC switching signal.

2. Opening signal: 4 20mA DC or 0 1.0K.

3. Control limit switch: open side and closed side.

4. Opening detection: precision conductive plastic potentiometer.

5. Power supply: 220VAC ± 10% 50Hz.

6. Driving motor: AC reversible single-phase gear reduction motor.

7. Output torque: 250Nm (DKJ-3100), 600Nm (DKJ-4100).

8. Output shaft rotation time: 40-100s (DKJ).

9. Effective rotation angle of output shaft: 900 (DKJ).

10. Thrust of output shaft: 4000 N (DKZ-3100), 6400 N (DKZ-4100).

11. Full travel time: 8-50s (DHZ).

12. Dead zone: 300A.