Home Improvement

Getting the Power to Control

One of the advantages of using machines to control processes

for you is that you can harness tremendous amounts of power

and energy which humans do not possess.

By a flick of a switch, huge sliding flood gates can move to

allow large quantities of water to flow out of a dam. With

just a slight twist on a handle, supertankers weighing

hundreds of thousands of tons are able to turn because of the

corresponding rotation of huge rudders.

Similarly, processes operating valves can be remotely operated

to control flow, temperatures, pressures and so on.

All these final control elements – flood gates, rudder,

valves – must be operated by actuators. The function of the

actuator is to move to control elements in the processes.

In order to move the actuator, there must be a medium for

transmitting the required power or action. All the actuators

are mechanical in nature. The common means of transmitting the

power are: pneumatic (air), hydraulic (fluid), and electrical


The actuators must be designed to work for that medium. There

are several advantages and disadvantages for choosing a

particular medium. For example, pneumatic actuators are

particularly useful when the atmosphere contains flammable

gases. By using pneumatic actuators, there is very little

chance that a spark can be generated to cause a fire. However

using air for actuating may be more expensive to install and

to maintain.

Using electrical motors to drive gearing may be an excellent

choice when cost is a consideration. Electrical wires can be

laid more easily and electrical systems are relatively clean.

Use of hydraulics may be excellent where power and simplicity

is important.

Most of the actuators operate in a linear (straight line)

manner. Hydraulic rams, and pneumatic diaphragms work in this

manner. There are also some that are constructed to operate

in a rotary manner.

Electrical motors normally operate in a rotary manner. However

if a linear motion is needed, this can be obtained by means

of spur gears, rack and pinion arrangements, crank and other


Actuators can provide the power to move final control elements,

but do they know when to stop?

A good control system will provide the sensing and feedback

loop to tell the actuator when to stop its actions.

Well folks, be in control!

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