Case Study: All Wash Function Timings Off

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Description of Problem:

Timing of wash functions is off and continues to get worse as vehicles progress through the tunnel.


Things to Check:

Were there any incidents that happened before the problem first began?


Confirm that the pulse sensor is adjusted properly.


Check if the pulse sensor input (input 09) on the PLC input card is flashing. It should be a steady, pulsing flash with no gabs between flashes.


Confirm that the pulse sensor proximity collar has all bolts in position. Standard configuration is either four or eight bolts (also called ‘Flags’) which are used to trigger the sensor


Pulse Sensor Information – CCS-T4647600


What is the Pulse Sensor?

The pulse sensor is one of the most important sensors in the wash


It is sometimes referred to as the heartbeat of the wash


It is an inductive proximity sensor, which means it detects metal objects (flags) to send a signal to the controller


For belt conveyor washes the sensor is located at the end of the wash on the driver’s side in the footwell. (See picture below)


For chain and roller conveyors the pulse sensor is either located in the conveyor hydraulic tank, or at the end of the wash near the drive sprocket

How Does it Work:

As the conveyor moves the pulse sensor detects the rotation of the metal flags, sending a signal which is monitored by the PLC. When the incoming vehicle blocks the photo eyes the pulse signals are counted and used to determine vehicle length, determining the timing through the entire wash.



It is important that the sensor be adjusted correctly, positioned within 1/4″ of the flag but not so close that the two will contact, as this will cause damage to the sensor.


If wash timing is accurate at the beginning of the tunnel but gets progressively worse as the vehicle nears the exit it may indicate a lost flag (broken or wiggled loose). Check the pulse (input 09) and be sure that it is moving smoothly and regularly without skipping any beats.


If replacing your sensor be sure to order the correct one. For those with Tommy Controllers, the correct part number is CCS-T4647600 and features a 3-wire cord (blue, brown, and black). A typical wiring diagram is included below.



If the pulse sensor ever fails it can be bypassed. Log into your controller and enter the pulse sensor menu. Change the “Enter Pulse Sensor Choice” number from 1 to 3 to enter Stand By Pulse. You may need to adjust the “Stand-By Pulse Rate” further. Larger numbers will slow the tunnel speed, while smaller numbers will speed the tunnel up.


Make sure that every time you change the belt speed you press the “Set Pulse” option to maintain the most accurate “Stand-by Pulse Rate”.


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