7/23/2019 Plc Examples Alternative Solution

http://slidepdf.com/reader/full/plc-examples-alternative-solution 1/2

PLC EXAMPLES

Example 1: Using AND and OR instructions

Output Y is ON if and only if the following expression is true:

((A&B)#(C&!D))&E

Example 2: A Standard Forward-Reverse Conveyor

The system is a simple conveyor run by a motor that can move in either direction. Theconveyor moves in the forward direction when output F is turned ON, and moves in the

backward direction if output B is turned ON.

There are two start buttons (one for each direction) called SF and SB, and a single stop

button called STOP. The user has to push STOP before  being able to change the

direction of motion of the conveyor.

There is also an overload sensor OL that stops the conveyor if the motor overheats.

The ladder logic program that is to be written should do the following: 

The conveyor starts moving when SF or SB is depressed (and is not yet moving) 

The conveyor stops moving when STOP is depressed or OL is ON

7/23/2019 Plc Examples Alternative Solution

http://slidepdf.com/reader/full/plc-examples-alternative-solution 2/2

Example 3: Same System using TIMERS

For safety reasons the conveyor only starts moving if either SF or SB are depressed for

more than 1 second (and is not moving yet)