PROGRAMMABLE LOGIC CONTROLLER (PLC) AND

AUTOMATION

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EJ501

UNIT 2bLOGICAL SENSORS AND ACTUATORS

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Objective

2. Logical Actuators Describe solenoid, valves, cylinders and motors. Explain solenoid, valves, cylinders and motors

operations. Use simple electro-hydraulics and electro-pneumatics

systems using logical actuators based on simple logical control/automation.

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Solenoid

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Valves

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Cylinder

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Motor

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Hydraulic

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Electro -HydraulicThe word electrohydraulic has two meanings for two highly different operations. It can stand for an electrical control device that makes precise adjustments in a hydraulic system. Also, it can mean a chemical reaction that is created by firing short, powerful electrical impulses into or directly beneath the surface of a body of liquid.

Perhaps the most well-known electrohydraulic device is an automobile's power steering unit — also called an electrohydraulic actuator. The unit combines high power with a high degree of accuracy to adjust for the minute movements of the steering wheel in a vehicle. This type of technology, where electrical components are used to increase the accuracy of hydraulic movements, can be applied to almost any situation where hydraulics is used.

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Electro -Hydraulic

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Pneumatic

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Electro - PneumaticThe electro-pneumatic action is a control system for pipe organs, whereby air pressure, controlled by an electric current and operated by the keys of an organ console, opens and closes valves within wind chests, allowing the pipes to speak. This system also allows the console to be physically detached from the organ itself. The only connection was via an electrical cable from the console to the relay, with some early organ consoles utilizing a separate wind supply to operate combination pistons.

The basic operation of the system is as follows: when the organist selects a stop and depresses a key, an electric circuit is completed, causing a low-voltage current to flow from depressed key, through the stop-tab switch, and on through the cable to the electro-pneumatic relay. The relay interprets the command from the console and sends an electric current to the appropriate solenoid. The solenoid is energized, causing the pipe valve connected to it to open, which emits compressed air into the pipe, allowing the pipe to speak.

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