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Lectu 04

The document describes examples of ladder logic programs for controlling various processes. It includes an example of controlling a drill press that requires two start switches to be activated along with a part sensor. Another example shows the logic for operating a door that opens and closes fully using limit switches, motor contactors, and indicator lights. A third example provides the sequence for operating three pneumatic pistons in a repeated pattern using solenoid valves when a switch is activated.

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326 views10 pages

Lectu 04

The document describes examples of ladder logic programs for controlling various processes. It includes an example of controlling a drill press that requires two start switches to be activated along with a part sensor. Another example shows the logic for operating a door that opens and closes fully using limit switches, motor contactors, and indicator lights. A third example provides the sequence for operating three pneumatic pistons in a repeated pattern using solenoid valves when a switch is activated.

Uploaded by

lana_salahadin
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Examples on Contacts and coils

Lecture 4
EXAMPLE 6-1
Figure 6-64 shows the sketch of a
drilling process that requires the drill
press to turn on only if there is a part
present and the operator has one hand on
each of the start switches. This
precaution will ensure that the operator’s
hands are not in the way of the drill.

The sequence of operation requires that


switches 1 and 2 and the part sensor all
be activated to make the drill motor
operate. Figure 6-65 shows the ladder
logic program required for the process
implemented using an SLC 500
controller.
• Reversing motor contactor for the up and down directions.
• Normally closed down limit switch to sense when the door is fully closed.
• Normally closed up limit switch to sense when the door is fully opened.
• Normally open door up button for the up direction.
• Normally open door down button for the down direction.
• Normally closed door stop button for stopping the door.
• Red door ajar light to signal when the door is partially open.
• Green door open light to signal when the door is fully open.
• Yellow door closed light to signal when the door is fully closed.

The sequence of operation requires that:


• When the up button is pushed, the up motor contactor energizes and the door travels
upward until the up limit switch is actuated.
• When the down button is pushed, the down motor contactor energizes and the door
travels down until the down limit switch is actuated.
• When the stop button is pushed, the motor stops. The motor must be stopped before it
can change direction.

Figure 6-66 shows the ladder logic program required for the operation implemented using
an SLC 500 controller.
Example: Sequencing of Pneumatic Pistons
The PLC task is to operate piston A followed by piston B followed by
piston C. The sequence is A+, A-, B+, B-, C+, C- is to be repeated
when switch SW1 is turned on
Solenoid valves do not work
• The wiring of solenoid valves is not correct or
not in the correct order (wiring problem)
• The ladder diagram is not properly written
(sequence in not correct)

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