Chemical Mixing Process using PLC

Design a PLC Ladder Logic for Chemical Mixing Process. We have RSLogix 500 PLC Programming software to create PLC logic and its simulation.

PLC Chemical Mixing Process

PLC Ladder Logic Chemical Mixing Process

Problem Logic

Step Conditions:
  1. Liquid A valve should ON till Sensor 2 activates
  2. Liquid B valve should ON between Sensor 1 and sensor 2 activation.
  3. After Sensor 2 activation, Stirrer motor should be ON for 10sec for stirring process.
  4. After stirring, Mixture output valve should open for 10sec.
  5. Process should continue still stop push button pressed.

List of Inputs and Outputs

3I:0/2Sensor 2Input
4I:0/3Sensor 1Input
5O:0/1Liquid A inlet Valve 1Output
6O:0/1Liquid B inlet Valve 1Output
7O:0/2Stirrer MotorOutput
8O:0/3Outlet ValveOutput
9B3:0Memory bitsMemory

PLC Program :

PLC Logic Mixer Project
PLC Chemical Mixer Ladder Logic

Ladder Logic Description


Latching rung to operate the system through Master Start and Stop PB.

RUNG001 and RUNG0002

To turn on liquid A input valve using memory bit of start latching PB, it will automatically turn off once Sensor 2 activates

RUNG 0003 and RUNG 0004

To turn on liquid B input valve using Sensor 2 activation, it will automatically turn off once Sensor 1 activates

Rung 0005

To store the status of Sensor 1, memory bit is used.

Rung 0006

On delay timer is used to run  the stirrer motor for 10 sec .

RUNG 0007

On delay timer is used to Outlet valve for 10 sec .

Program runs continuously until STOP PB is pressed.

  1. Memory bits are used to store the sensor output, since it is the simulation, sensor cannot turn off automatically.
  2. Memory bits are used to get the sequence of operation.


The above explained Chemical Mixing process is for example only. It may vary from real time. We can use this example program to understand the working of timers, memory bit and interlocking concept function in AB PLC.

Author : Hema Deepan

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