chapter 09 - electrical controls

8/11/2019 Chapter 09 - Electrical Controls

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ELECTRICAL CONTROLSELECTRICAL CONTROLS

byby

EngrEngr. Alexis T.. Alexis T. BelonioBelonio

Department of Agricultural EngineeringDepartment of Agricultural Engineeringand Environmental Managementand Environmental Management

College of AgricultureCollege of Agriculture

Central Philippine UniversityCentral Philippine University

Iloilo CityIloilo City

[email protected]@yahoo.com


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IntroductionIntroduction

The success of any electrical applicationThe success of any electrical application

highly depends upon the proper selectionhighly depends upon the proper selectionof a control mechanism in operating theof a control mechanism in operating the

equipment.equipment.


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Electric Brooder

Dehumidifier

Freezer

Air ConditionerFood Dehydrator


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Classifications of ElectricalClassifications of Electrical

Control MechanismControl Mechanism Manually Operated ControlsManually Operated Controls

SwitchesSwitches AC RelaysAC Relays

PushbuttonsPushbuttons

Motor Starting SwitchMotor Starting Switch

Magnetic Starting SwitchMagnetic Starting Switch

Reduce Voltage StartersReduce Voltage Starters

Solenoid ValveSolenoid Valve

Automatically Operated ControlsAutomatically Operated Controls ThermostatThermostat

Time Float SwitchTime Float Switch

Pressure SwitchPressure Switch

Limit SwitchLimit Switch


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SwitchesSwitches

It is the most basic electrical controlIt is the most basic electrical control

mechanism.mechanism. It is used to open and close theIt is used to open and close the

circuit.circuit. Its contact must open and closeIts contact must open and close

quickly snapquickly snap--action the circuit.action the circuit.


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Nomenclature for SwitchesNomenclature for Switches

SingleSingle--pole singlepole single--throwthrow

DoubleDouble--pole, singlepole, single--throwthrow

TripleTriple--pole, singlepole, single--throwthrow

SingleSingle--pole, doublepole, double--throwthrow DoubleDouble--pole, doublepole, double--throwthrow

TripleTriple--pole, doublepole, double--throwthrow


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Single Pole DoubleThrow

Single PoleSingle Throw


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AC RelaysAC Relays

It is a type of switch having contacts which areIt is a type of switch having contacts which areoperated by magnetism which allows the currentoperated by magnetism which allows the currentto pass through a coil of the wire. Magnetism isto pass through a coil of the wire. Magnetism isremoved once the the flow of current through theremoved once the the flow of current through thecoil is stopped.coil is stopped.

The electrical input to the appliance is controlledThe electrical input to the appliance is controlledby the relay contacts.by the relay contacts.

The current rating of the contacts is veryThe current rating of the contacts is veryimportant, and the proper selection dependsimportant, and the proper selection dependsupon the current flow to the appliance which isupon the current flow to the appliance which is

to be controlled.to be controlled.


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Solid State Relay


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The main advantage in using the relay isThe main advantage in using the relay is

that the switch and wires which controlthat the switch and wires which controlthe current flow to the relay coil do notthe current flow to the relay coil do not

conduct the current to the appliance.conduct the current to the appliance.

Relays are adapted for controllingRelays are adapted for controllingmotors, heaters, and large lighting loadsmotors, heaters, and large lighting loads

for remotely located smallfor remotely located small--size switches.size switches.


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PushbuttonsPushbuttons

It is a manually operated type of switch forIt is a manually operated type of switch for

starting and stopping electric motorsstarting and stopping electric motors It is also used for operating the electricIt is also used for operating the electric

relay type of circuit.relay type of circuit.


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Motor Starting SwitchMotor Starting Switch

It is used to control and protects theIt is used to control and protects the

electric motor.electric motor. It has a builtIt has a built--in overload device thatin overload device that

automatically trips the switch in case thereautomatically trips the switch in case thereis too much current flowing into the motor.is too much current flowing into the motor.


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Magnetic Starting SwitchMagnetic Starting Switch

It is used primarily for starting 1It is used primarily for starting 1--hp and largerhp and larger

size motor.size motor. It can also be used for connecting large heatingIt can also be used for connecting large heating

or lighting loads to the source of power.or lighting loads to the source of power.

This switch incorporates into one complete unitThis switch incorporates into one complete unitthe principle of relay coil, the overhead stripper,the principle of relay coil, the overhead stripper,

and the push button control.and the push button control.


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Solenoid ValveSolenoid Valve

It is operated by electricity but the valve itself doesIt is operated by electricity but the valve itself doesnot control the flow of the electricity. Instead itnot control the flow of the electricity. Instead it

controls the flow of water, oil, or gas.controls the flow of water, oil, or gas. It is useful for fuel supply line, refrigeration system,It is useful for fuel supply line, refrigeration system,

humidifier, water supply line, etc.humidifier, water supply line, etc.

The only electric power required for this control isThe only electric power required for this control isabout 7 watts hence the cost is negligible.about 7 watts hence the cost is negligible.

The switch maybe manually or automaticallyThe switch maybe manually or automaticallyoperated. When current flow the coil, it causes theoperated. When current flow the coil, it causes themetal plunger by magnetism to be drawn up into themetal plunger by magnetism to be drawn up into thecoil.coil.


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Solenoid Valve Automatic Ball Valves

Mass Flow ControllerFlow Switch


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ThermostatThermostat

It is a special kind of switch wherein it s contactIt is a special kind of switch wherein it s contactopen and close automatically in response toopen and close automatically in response tochanges in temperature.changes in temperature.

It is an automatic switch which is used forIt is an automatic switch which is used fortemperature control.temperature control.

Classifications are:Classifications are:

Bellow ThermostatBellow Thermostat

Bimetallic ThermostatBimetallic Thermostat Wafer ThermostatWafer Thermostat


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Temperature Controller

Thermostat


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Line Voltage

Thermostat


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Time SwitchTime Switch

It is an electric clock that automaticallyIt is an electric clock that automatically

operates switch contacts at definite timeoperates switch contacts at definite timeintervals.intervals.

The general purpose time switch is designedThe general purpose time switch is designed

automatically to close the switch contact twoautomatically to close the switch contact twotimes and open them two times during any 24times and open them two times during any 24hour period.hour period.

Usually they are use to switch ON and OFFUsually they are use to switch ON and OFFlighting facility for farm houses, automaticlighting facility for farm houses, automaticfeeders, cooling systems, hay curing, grainfeeders, cooling systems, hay curing, grain

drying, and heating systemsdrying, and heating systems


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Float

Paddle Level Switch Float Switch


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Pressure SwitchPressure Switch

It is an automatic control having a switch contacts whichIt is an automatic control having a switch contacts which

are operated according to variations in liquid or gasare operated according to variations in liquid or gas

pressure.pressure.

The gas, vapor, or liquid passes through the control, andThe gas, vapor, or liquid passes through the control, and

the pressure of the gas or liquid expands the metalthe pressure of the gas or liquid expands the metal

bellows against the force of a spring.bellows against the force of a spring. Common application of this type of switch is the pressureCommon application of this type of switch is the pressure

tank run by electric pump for domestic water supply.tank run by electric pump for domestic water supply.


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Gas Pressure Switch

Bourdon PressureSwitch


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Limit SwitchLimit Switch

It is an electric switch which is operatedIt is an electric switch which is operated

automatically by the movement of some otherautomatically by the movement of some other

piece of material or machine.piece of material or machine.

The switch mechanism is frequently tripped by aThe switch mechanism is frequently tripped by a

knot in a rope, a metal stop fastened to a chin, aknot in a rope, a metal stop fastened to a chin, acam, or some similar specially riggedcam, or some similar specially rigged

arrangement.arrangement.

Switch contact are normally returned to theirSwitch contact are normally returned to theirnormal position by the action of spring.normal position by the action of spring.


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R fR f


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ReferenceReference

Brown, R. 1956. Farm Electrification. McGrawBrown, R. 1956. Farm Electrification. McGraw--HillHill

Book Company. New York. 367pp.Book Company. New York. 367pp.

chapter 09 - electrical controls

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