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# Electrical Engineering Terms P

Power Supply

A transformer and rectifier circuit are encased together to supply a lower control voltage.

Programmable Logic Controllers

An industrial computer that is used to control and execute real-world functions based on the programmed logic.

Power Supply

Provides power to the PLC and converts the incoming powers to various voltage levels.

Programming Device

A unit designed to develop and deliver programming logic to a PLC.

Percent Slip (%-slip).

As used with AC electric motors, the difference between the synchronous speed of the rotating electromagnetic field created within the confines of the stator assembly and the actual running or turning speed of the rotor, divided by the synchronous speed and then multiplied by 100. The amount of or %-slip is governed by the torque requirements of the mechanical load driven by the electric motor. It varies from almost 0% slip with the motor operating with no load, to 100% slip when the motor is mechanically overloaded and the rotor stops turning (locked-rotor).

Periodic Duty.

If an electric motor is nameplate-rated with this type of duty cycle, it is rated to operate intermittently and the load conditions are regularly recurrent.

Phase.

Indicates the number of phases required in the electrical supply that a given AC induction motor is designed to operate.

Power Factor (pf).

Normally abbreviated to the acronym pf, this term describes the correction coefficient for AC power necessary because of the changing values of current and voltage. It is the ratio (or comparison) of the wattage or true power (useful work) in an AC circuit or AC-supplied equipment to the total volt-amps or apparent power flowing in the circuit or supplied to the equipment.

Polarity.

The characteristics of an electrical or electronic device that exhibits opposite quantities, normally positive and negative, within itself.

Power Limited.

A control transformer is described as a power limited because the nameplate VA rating is the maximum power that will be dissipated from the transformer core (in the form of heat) should the secondary terminals become accidentally shorted.

Power rating

It is the maximum amount of power they can dissipate before they become damaged by the heat buildup.

Phase

An angular measurement that tells the position of a sine wave with respect to something, usually the origin.