Programmable Logic Controller - Lets Solve a Sequential Problem

Lets try and solve a sequential problem in this blog post.

Example of a Sequential Process

In the process shown in figure we want to fill the two tanks with water using a pump.

• Prepare Ladder logic program to implement the following sequential control application.
• Start/Stop push buttons controls On/Off of the Pump.
• Valve 1 alone will be kept open till the tank 1 gets filled or for a period of 10secs.
• Then Valve 2 will be kept open till tank 2 gets filled or for a period of 15 secs.
• After the above sequence stop the pump.

Input – Output Allocation - Sequential Control Application

<Relay>
<No.> <Label> <Comment1> <Comment2> <Comment3>
0000 :START Start Push Button
0001 :STOP Stop Push Button
0002 :SENSOR1 Sensor for Tank 1
0003 :SENSOR2 Sensor for Tank 2
0500 :PUMP Pump Output
0501 :VALVE1 Valve 1 Output
0502 :VALVE2 Valve 2 Output
<Timer>
<No.> <Label> <Comment1> <Comment2> <Comment3>
T000 :TIMER1 Timer for Valve 1
T001 :TIMER2 Timer for Valve 2

Ladder Program - Sequential Control Application

Lets shift to a Conveyor Belt Applicaiton

Prepare a Ladder Logic to implement the given conveyor system:

• There are 2 conveyors: one carries filled water bottles and another one carries empty boxes. We have to pack 10 bottles in each box.
• The bottle carrying conveyor runs continuously.
• The box carrying conveyor stops for packing (10 bottles) and runs 2 sec for next box.
• Stop the system when 25 boxes are packed.
• Also provide a manual stop button.

Input-Output Allocation - Conveyor Application

<Relay>
<No.> <Label> <Comment1> <Comment2> <Comment3>
0000 :START Start Push Button
0001 :STOP Stop Push Button
0002 :SENSOR1 Sensor for Bottles
0010 :DUMMYC1 Dummy for Counter 1
0011 :DUMMYC2 Dummy for Counter 2
0500 :WCONVEYO Water Bottle Conveyor
0501 :BCONVEYO Boxes Conveyor
<Counter>
<No.> <Label> <Comment1> <Comment2> <Comment3>
C200 :WCOUNTER Counter for Water Bottles
C201 :BCOUNTER Counter for Boxes

Ladder Logic - Conveyor Application