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Types of Controls:
In ensuing lines we will discuss about the various forms of control circuits and types of devices used in the normal day to day life pertaining to the field of Electrical Engineering.
1. MANUAL CONTROL :
The link between the measuring element and the regulating unit is the human operator. In this type of control no automatic controls are used in the system. This type of system might be very simple to implement but the only drawback being that such a system needs constant human monitoring and vigilance.
2. SEMI-AUTOMATIC CONTROLS :
The human operator starts off a sequence of operations which are then carried out automatically in some predetermined manner. For example starting up an electric motor by pressing the start button or in start up a process in which the valves are operated in a definite sequence at fixed time interval by a timer.
3. AUTOMATIC CONTROL :
There is no human link between the measuring unit and the regulating unit. Hence the operator is replaced by the controller. This action is continuously variable and remote. Automatic control system is one in which the actual value of the controlled parameter (such as pressure, temperature, flow, level etc) is compared with a desired value and corrective action is taken depending upon the deviation between the two values without the inclusion of a human element. It includes both the measuring means as well as the controlling means and both are done automatically by the system itself, hence the nomenclature.
4. LOCAL CONTROL :
The regulating units is altered by means of a lever, hand wheel or other attachments fixed on the unit itself.
Some means of power transmission is used to connect the regulating unit to an actuating device mounted some distance away. The power transmission may be either through mechanical linkages, fluid linkages or electrical linkages.
6. ON/OFF CONTROL :
The regulating unit occupies only one of the available two extreme positions (as in case of electrical relay or switch). A very common example of this is the normal manual on-off switch that we use in our houses to turn on the lights and turn them off.
7. STEP- by -STEP CONTROL :
The regulating unit can occupy more than two positions but as the name implies, the action is not continuous and occurs in jerks or steps as in the case of notches on a speed regulator or starter of an electrical motor.
8. CONTINUOUSLY VARIABLE CONTROL :
The regulating unit can be at rest in any position between two definite limits as in slider of potentiometer slide wire to convert the vertical, horizontal and angular motion in to the voltage difference to check the set value and operate accordingly.
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References & Image Credits
Continuous Interaction and Manual Control, http://www.ercim.eu/publication/Ercim_News/enw40/doherty.html
Automatic Control, http://automatic-control.co.tv/
By espensorvik, http://www.flickr.com/photos/28478778@N05/5728485497/