Programming A Plc:Operation of the Circuit

Operation of the Circuit

The circuit operates in the following manner: When the pressure switch closes, all 0 inputs change position. This provides a current path to timer T600, which begins timing. A current path is provided to output 10, which turns on the warning light, and a current path is provided to the audible alarm, turning it on. The normally open 0 contact connected in series with coil 160

closes. At the end of a half second, timer T600 times out and changes the position of all T600 contacts. The normally closed contact connected in series with the warning light opens and turns off output 10. The normally open T600 contact closes and permits timer T601 to begin timing. At the end of a half second, timer T601 opens its normally closed contact connected in series with timer T600. This causes timer T600 to reset and return all of its contacts to their


normal position. The normally closed T600 contact permits output 10 to turn on again, and the normally open T600 contact resets timer T601. When timer T601 resets, its contact returns to its normal position, and timer T600 begins timing again.

This condition continues until the operator presses the acknowledge button, causing input contact 1 to close. Contact 1 completes a current path to internal relay 160. When internal relay 160 energizes, the normally open 160 contact closes and seals the circuit around contact 1. The normally closed 160 contact opens and turns off the audible alarm. At this time in the circuit, the audible alarm has been turned off, but the warning light is flash- ing on and off at half-second intervals. This will continue until the pressure drops to a safe level and input 0 reopens all of its contacts, causing the circuit to reset to its normal position.


Ahmed Farahat is EECS engineer With 18 years of experience in the field he worked on different technological discipline and and had honored Post Graduate Diploma In Computer Science And Engineering

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