Electric Actuator Controls

Electric valve actuators control the opening and closing of valves. With a motor drive that provides torque to operate the valve, these actuators are frequently used on multi-turn valves such as gate or globe and also on ball, plug and other quarter-turn valves. Valves

This article will review different types of control systema and configurations available to clectrically operate valve, which some in the industry refer to as motor-operated valves (MOVa), and how to make an informed decision an which type of actuator to use.
Electric valve actuators are ubiquitous in today’s industrial space. They can be found in various industries and applications, including water treatment and wastewater plants, hydroelectric power generation, oil refineries, shipbuilding and numerous processing industrica such as chemicals, food and beverage, pulp and paper, and pharmaceuticals. For anyone charged with the selection and operation of these products, it is important to understand the power source, controls, feedback, commissioning, security backup power and failsafe required for the application.

POWER SOURCE

An electric setuzior must have a power source available. Prior to selecting an actuator, it is important to determine the type of electricity that is available on sites.

• Single-phase AC power
• Three-phase AC power
• DC power

This will decide the type of electric actuator supplied for the application. The power source will be used to operate the moter through a act of reversing contacters, cither located within the actuator, or in some cases located in a remote cabinet.
The power source must be capable of supplying the proger voltage and current required by the electric actuator to operate the valve. An electric setuntor may be required to operate the valve as an open close or modulating actusior; make sure the actuator is manufactured and supplied according to the required specifications.

For example, today’s power plant designers are integrating asset management technology into their plant designs as a focal point for improved operational performance. In doing so, they are introducing sophisticated electronic controls found in such devices as the latest generation of valve actuators to provide vital diagnostic and performance information to the control room.

While the benefits of diagnostic monitoring and automated control are impressive, many seasoned plant engineers may ask: “Can these devices survive in a power plant environment? ” In short, the answer for many applications is “Yes. ” However, there are exceptions, and this booklet will help give insights to clarify specific situations. Another pressing question arises with existing power plants that are under mandate to increase efficiency both operationally and environmentally. Its ce-Many retrofit projects involve re-automating existing valves, gates, and dampers. The question is, “Do you replace like with like,” or “Do you look at new technology?

” In facts, there are significant advantages to using new technology in an older plant environment to improve the performance of a single process. This booklet will provide useful information on some of the available options.

CONTROLS

Controls are what operate the electric actuator so the next step is to determins how the actuator will be controllied.
There are two main types of controls
• Local controls are mounted directly to the actuator. Photo 1.0
• Remote controls are systems that operats the actusier remotely.

CONTROLS

Remote Control Types

Actuator-mounted local controls. All photes courtesy of AUMA

Discreet open and close signala from a PLC or other ayatem are most commonly used with open/close valves and can be used for modulating service sa well. This is dene with open step close signals aent from pushbuttons or switches (gilet devices) from the PLC or remoto-control station to the actuator. Control power is typically a 24VDC or 110VAC signal. Remote-control power can be provided on-site, or in some caacs, actuators come equipped with a control power transformer (CPT) that provides this voltage for the customer’s central system to sac.

Analog control signals are common with modulsting valves. The analog control signal can also be referred to as a positioning signal or act paint. Mest analog controla utilize a 4-20mA signal, with 4mA being fully closed and 20mA being fully open. A 0-20mA is typically not ward because OmA could be misinterpreted as a loss of signal. The valve’s position in between clase and open can be reached by actting the mA control signal to a signal position in between 4mA and 20mA, respectively

Remote control System

FEEDBACK

Feedback are the signals coming from the actuator to the control system, alse referred to as output signala.
Analog feedback. Actuators can supply
4-20mA signal to give the control system the existing valve position, like
the setpoint analog control signal. 4mA ar 20mA may be set to indicate the open er close pasition based on the application. Some actuators can also offer torque feadbuck in the form of a 4-20mA signal indicating actuator output torqut, if the application requires.
Discreet feedback signals. Many actustors have status relays available to the customer signaling actuator position, torque-fwalt, general fault, ran indiestion or intermediate position. In the case of non-intrusive (defined below in Commissioning) setunters, they will have relays that can be programmed to the customer’s desirod feedback signal requirements.
Bus communication fredenck. Fieldrus monitering can be done across the fieldbus signal to include many meer signals than art capable using the discreet fecdluck. For example, this can be the actuator’s position or status, and fieldbus system status, in addition to many others depending on the fieldlrua protocol.
Limit torque switches. Theet art available as voltage-froc dry contacta to give position tarque feedback status.
Visual position feedback. Mest actuators come with a physical position indicator that shows the position of the valve and actuater, this may be in the form of a mechanical dial or on-screen indication. If the valve actuator is mounted to an additional gearbes, it efien is supplied with a pointer caver to offer visual pesition indication

COMMISSIONING

Visual position feedback screen.

Commissioning of an actuator is required to ensure proper eparation of the valve and integration to the control system. Commissioning requirements may include verification or setting of end positions, acting of torque and the feedback signals. Commissiening is performed based on the type of actuator provided.

•Intrusive actuators. These actuators must have the covers opened, and tools are used to act the limit rouches and torque switches in the actuator.

•Non-intrusive actuators. Thear smart actusters can be programmed using the local controls. Additional options, such as a Bluetooth and a laptop, a mobile phone app, or other device may also be used to perform the commissioning

SECURITY

There are different levels of security available for the customer when it comes to an cloctric actuator
Physical security: Actuaters can be supplied with lockable pilet deviers, such as selector switches. Additionally, lockable covers may be supplied to cover the local controls. There is also the option to have padlocks on the handwheel/declutch devices, which are used to operate the valve manually

Visual merkanical position feedbacke indicator

System security

Hands-on and/or wireless commissioning

•Bluetooth – The ability to turn the Bluetooth on off, password protect or eliminate it entirely may be an option.

•Permissive signal – When seming up a control system a permissive signal can be given to the setunter before it will operate electrically. This can be ward to ensure the valve is nat accidentally operated.

• interlock signal – A permissive signal is supplied to the actuster som a separate actuater or other device within a facility. This interlock is used if opening or closing the valve requires a defined status clarshare in the facility.

BACKUP POWER

Backup or emergency power may be important in an instance where the main power on-site is interrupted. A decision must be made as to the type of actuator operation required upon the loss of
main power. Does the actuator still need to operate the valve normally or just place the valve in a safe position?
These options can operate the actuator and/or place the actuator in a safe position in a loss of main power:
UPS (Uninterrupted Power Supply): If a solution for actuator normal operation during a power outage is needed, a UPS backup power system could be a good option for the actuator. This will allow a customer to open or close the valve in the event of an emergency power outage. DC (Direct Current Power): Actuators are also available in a DC voltage version. These can be used if a site has backup DC voltage available to operate an actuator during an emergency power outage.

Actuator and hand wheel with look and an alarmative option for a faceplane zover. Photo credit courtesy of AUMA

FAIL SAFE

An actuator may be supplied with a device to place it in a safe position. This device often uses a spring or other technology to place the actuator in the defined safe position.

BEST PRACTICES

An actuator may be supplied with a device to place it in a safe position. This device often uses a spring or other technology to place the actuator in the defined safe position. Power Source

” Ensure the site has the power and current available to operate the actuator supplied.“

“Separate power cables from signal cables.”

Type of Controls

” Make sure the actuator is supplied to match the controls available at site.

Feedback

” Ensure the actuator is supplied with the proper feedback for the application.

” Ensure that you know who is supplying the analog feedback power.

Commissioning

” Always employ a trained professional familiar with the equipment supplied.”

Security

” Keep track of changes to actuator passwords. OEMs may be capable of resetting passwords back to factory default.”

Backup Power

” Make sure the actuator and backup power sources are compatible (voltage, current, etc.) “

Failsafe

” Make sure the actuator is supplied with the desired failsafe position. The failure position may not be changeable after delivery”

Electric actuators have an important role in safe and efficient operation valve operation. Understanding the various elements, such as those discussed here, allow the user to successfully define, set up and operate a basic control system. In the realm of industrial automation, electric actuators are a standout solution renowned for their superior precision, adaptability, and energy efficiency. Offering precise control over speed, position, and force, they excel in dynamic operating conditions, making them ideal for applications that demand fine control. The surge in their popularity is attributed to their on- demand energy consumption and eco- friendly design, aligning with new global regulations seeking sustainable solutions across industries, especially in the industrial sector. The use of electricity opens doors to leveraging renewable energy sources like solar and wind. Their streamlined design and reduced maintenance requirements further increase their appeal, positioning electric actuators as one of the main choices when seeking efficient, environmentally friendly, and low-maintenance automation solutions.

Author Jeremy Payne, Engineering

Team Leader, Auma Actuators

Courtesy : Valve Magazine