Slide
Controlling Electric
Actuators
Industrial grade electric actuators have specific requirements for controlling the position of
the actuator.
Motors for Electric Actuators
=>
Continuous Service—Servo motors and brushless DC motors (BLDC) can start and stop continuously.
=>
Intermittent Service—AC/DC brushed motors and series wound motors can operate only a percentage of time in a given time frame to protect the motor from overheating. The percentage of operating time is known as the duty cycle. Duty cycle is very important in actuator control because the system must operate the actuator in such a way so the duty cycle is not violated.
Control Systems
There is a hierarchy of control systems used in industrial processes
System
Description
PLCs (Programmable Logic Controllers):
PLC’s are the basic building blocks of automation, handling individual machines or processes. They execute pre-programmed logic based on input signals and controlling outputs.
DCS (Distributed Control System)
DCS systems integrate multiple PLCs and other components to manage large-scale, complex
processes. They provide a more centralized control and monitoring than PLCs alone,
SCADA (Supervisory Control
and Data Acquisition)
SCADA provides a supervisory level for remote monitoring, data acquisition, and control. It
connects to PLCs and DCS systems to collect data, display information to operators, and send
commands for control.
Electric Actuators Control Methods
Open/Close/Jog with Limit Switches
=>
Actuators drive to an end of travel limit switch that stops movement at predefined end points. For a quarter turn actuator mounted on a valve, the end of travel is usually 0° and 90° for close and open, respectively. The actuator may be controlled only to the end of travel location (open or close) or may be controlled to stop at some location between the designated end of travel (jog function).
Proportional (Modulating) Control
=>
In Proportional, also known as Modulating, Control, the control system sends a signal to the actuator to drive the actuator to where control wants the actuator to be. Typical signal ranges are 4-20mA, 0-10VDC, 2-10VDC, 1-5VDC and 0-135Ohm. The position between 0 and 100% of the travel of the actuator is directly related to the value of the signal.
Networked or Bus Control
=>
The actuator is part of an industrial communication network such as a SCADA system where control follows a communication protocol, such as Modbus, to communicate and control the actuator. Each actuator has a specific address and is controlled when the bus signal indicates the actuators address.
Position Feedback
=>
Actuator can have a feedback or position system that indicates its actual position (via potentiometer, encoder, etc.). The control system will use that information to determine the offset between where the actuator should be and where it is. The control system then directs the actuator to match a desired position. Feedback can be used with any of the control methods, but is usually essential for Proportional and Bus Control.
16138 Flight Path Drive Brooksville, Florida 34604 ⚫ P(352) 544-8436 F(352) 544-8439
www.promationei.com