Functions:

Automatic shutdown in the positions of the end After receiving a command operation, the actuator moves the valve in the direction to open or close. When he reached the final position, an automatic shutdown procedure is started. Switch-off two fundamentally different mechanisms may be used. The checks turn off the actuator when the point of intervention has been achieved. This is called limit down.

However, there are types of valves for the element of closure shall be displaced in a defined end to a force or a torque defined to ensure that the valve seals tight. This is called down torque. The controls are programmed to ensure that the actuator is switched off when it exceeds the limit of torque. The signal's final position limit switch is used to indicate the final position. Security Features Switching pair is not only used for sessions of the couple in the final position, but also serves as protection against overload over the entire race and protects the valve against excessive torque.

If the acts of excessive torque on the closing element in an intermediate position, for example, because an object in a trap, trip-switching pair when it reaches the set of action of torque. In this situation the final position is not reported by the limit switch. The controls can then distinguish between normal operation torque switch tripped in one of the final positions on and off in between due to excessive torque.

Temperature sensors are required to protect the motor against overheating. For some applications from other manufacturers, the increase in motor current is controlled. Thermoswitches or PTC thermistors that are embedded in the windings of the motor for the most reliably fulfill this task. Shooting, when the temperature limit has been exceeded and controls to turn off the engine. The position [1] is supplied with a set point [2] and an actual value [3]. The motor is controlled until the actual value is identical to the setpoint. The DCS needs generally a return signal [4], the functions of process control.

Due to an increasing decentralization in automation technology and the introduction of micro-processors, more and more functions have been transferred from the DCS to field devices. The volume of data to be transmitted has been reduced accordingly, in particular with the introduction of fieldbus technology. Electric actuators, whose functions were also expanded significantly affected by this development.

The simplest example is control of position. Positioners are equipped with modern self-adaptation that is the positioning behavior is constantly monitored and optimized by the parameters of the controller. Meanwhile, electric actuators are equipped with full-controllers actual process (PID controllers). In particular for remote installations, such as flow control for a large reservoir, the actuator may take over the tasks of a PLC, which otherwise would also be installed. Diagnosis The diagnostic feature on two counts. Actuators have large modern diagnostics to help identify the cause of a failure. The second function is the recording of the operation. The evaluation of the data allows to draw conclusions on the previous year. Working on this basis, the operation can be optimized by changing the parameters and the wear on the actuator and the valve is reduced.

Duty types:

Typical time period in open-close duty. T1 is the time of operation and can not exceed the maximum allowable execution time Period of time typical in modulating duty. Open-close duty If the valves are used as shutoff valves, the valve is open or closed. Intermediate positions are not approached. The valve is seldom operated, the interval between the operations can be within minutes or even several months. The 'Short-time duty S2' mode of operation of the electric motor in accordance with IEC 34-1 indicates that the actuator is suitable for this type of applications. Another feature of this duty is the maximum permissible duration without interruption. A typical time for actuators is 15 min. Positioning duty Define the intermediate positions are approached to establish a static flow through a pipeline. Performs the same terms as open-close duty apply. ]

Modulating duty:

The most distinctive characteristic of a closed-loop is an application that changing conditions require frequent adjustments to MOV for example set a certain rate of flow. Sensitive closed-loop applications require adjustments within few seconds. Requests for the actuator is greater than open-close or duty positioning. Both the mechanics and the engine must be designed so as to be able to withstand the high number of starts without any degradation in accuracy of control. The type of duty electric motor suitable for this application is called intermittent intermittent duty S4 or S5.

The running time is limited by its about time, for modulating actuators this is usually 25%. Electric actuators are used all over the world, in all climatic zones, in all types of industrial facilities in specific local environmental conditions. Applications are often linked to security, therefore, the plant operators placed high demands on the reliability of the devices. Failure of an actuator can cause accidents in process control plants and may leak toxic substances into the environment.

Process of controlled installations are often used for several decades and that justifies the demands placed on longer-life devices. Closet The types of protective custody are settled according to the so-called IP Code of EN 60529. The basic version of most electric actuators is already designed the second highest enclosure protection IP 67. This means they are protected against the ingress of dust and water during the dive (30 min to a max. Water column of 1 m). Most manufacturers also supply the actuator protective enclosure IP 68, which provide protection against immersion up to a max. water column of 6 m. Ambient temperature In Siberia, temperatures up to - 60 ° C may occur in plants with technical process +100 ° C can be overcome.

Using the correct lubricant is essential for full operation in these conditions. Fats that can be used at room temperature becomes too solid at low temperatures so that the actuator can not overcome the resistance within the device. At high temperatures, these fats are Liquify and lose their lubricity. The sizing of the actuator, the temperature and the selection of the lubricant are of great importance.

Explosion protection:

Electric actuators are used in applications where potentially explosive atmospheres may occur.

This includes among other refineries, pipelines, oil and gas or mining. Where the potentially explosive gas-air mixtures or dust-gas mixtures occur, the actuator can not act as a source of ignition. Basically, hot surfaces on the actuator as well as the ignition sparks created by the actuator must be avoided. This can be achieved by an explosion-proof enclosure, for example, that the housing is designed to prevent ignition sparks to leave the house even in the event of an explosion inside. Actuators designed for these applications, as explosion-proof devices should be classified by the test authority (notified body).

There is no such thing as a uniform standard throughout the world, according to the country in which the actuators are used, several directives and regulations must be respected. Within the EU, ATEX 94/9/EC applies to the United States, NEC (approved by FM) or the CEC in Canada (approved by the CSA). Explosion-proof actuators must meet the design requirements of these directives and regulations.

Additional uses Small electric actuators can be used in a wide range of assembly, packaging and test applications. These actuators can be linear, rotary, or a combination of both, and can be combined to perform the work in three dimensions. Actuators of this type are often used to replace the pneumatic cylinders.