PLC Program to Implement an Automatic Car-Wash Process


This is a PLC Program to Implement an Automatic Car-Wash Process.

Problem Description

When a Car enters the hall, a certain sequence is to be followed automatically. Steps are, 1) Soaping, 2) Washing, 3) Rinsing and 4) Drying. Implement this process sequence in PLC using Ladder Diagram programming language.

Problem Solution
  • To detect the car automatically, load cells can be used, or any other sensor such as Infrared Sensor can also be used.
  • Soaping, Washing, Rinsing and Drying are performed for a particular time, hence to generate time delay for these outputs become mandatory.
  • To operate this process, for soaping, washing, and drying, four different timers are used.
  • IR sensor detects everything whatever restricts the signal but in load cell, particular Low Level and High Level can be set to detect heavily weighted cars only. Load Cell can be here more effective here than IR sensors.
PLC Program

Here is PLC program to Implement an Automatic Car-Wash Process, along with program explanation and run time test cases.

List of Inputs and Outputs
 I:1/0	= Master Start			(Input)
 I:1/1	=  Car Detection		(Input)
 I:1/2	= Limit Switch, Conveyor	(Input)
 I:1/3	=  Master Stop			(Input)
 O:2/0	= Master Coil			(Output)
 O:2/1	= Soap Sprinkler		(Output)
 O:2/2	= Washer			(Output)
 O:2/3	= Conveyor			(Output)
 O:2/4	= Dryer				(Output)
 T4:0 	= Soaping Time			(Timer)
 T4:1	= Washing Time			(Timer)
 T4:2	= Drying Time			(Timer)

Ladder Diagram for Automatic Car Wash Processplc-program-implement-automatic-car-wash-process-01plc-program-implement-automatic-car-wash-process-02

Program Description
  • RUNG000: This rung is used to create a Master Coil, in other words, Master Start and Stop which controls the entire system. To activate this system, this Master Start has to be pressed.
  • RUNG001 is used to activate Soaping process which is operated by a switch input I:1/1, when car is detected, Soap sprinklers are activated. And RUNG002 is used to generate a time delay which terminates the Soaping process by using XIO of T4:0/DN bit after a definite time.
  • As soon as Soaping is done, RUNG003 has Washing outputs which washes the car by water sprinklers and RUNG004 is used to generate a time delay which terminates the washing process by using XIO of T4:1/DN bit after a definite time.
  • RUNG005 is activated as soon as the washing process is done. It has motor coil’s output to run the conveyer on which car moves to the last step of car washing, drying of car. At the end of the conveyor, a limit switch is mounted which stops the conveyor and till then Drying is done through RUNG006 and RUNG007 similar to previous operations.
Runtime Test Cases
  • You can simulate this process on LogixPro and check all the Test Cases.
  • Choose I/O Simulation and simulate this program. Worst cases are checked.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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