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Tunnel vision: Back to basics

October 11, 2010
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Carwash tunnels contain many complex machines that must work together to wash a car. Most tunnel controllers are comprised of three parts:

  1. A microprocessor-powered controller that directs all outputs and inputs;
  2. A series of low-voltage relay outputs and inputs; and
  3. An entrance keypad.

The parts and soul of a tunnel
To understand the carwash tunnel, we begin with the microprocessor-powered controller. The controller acts as the director of the show.

Initially, the entire wash sequence is programmed into the controller through either the entrance keypad or a computer interface.

To work properly, a controller must have effective two-way communication. It must receive information, such as gate switch (to determine vehicle length) and pulse switch (to determine conveyor speed), through input relays.

The controller then uses that information to communicate with the tunnel. It does this through the output relays.

After determining the length of the car and the speed of the conveyor belt, the controller will send a message through an output relay to direct each item in the tunnel to turn on when the car hits a certain point.

For example, the rinse arch will stay on for the length of the car and then the relay will turn off the arch when the car has passed. It is this simultaneous processing of inputs and outputs that creates a coordinated wash.

Tunnel controllers are usually sold by the number of outputs or functions they contain.

The controllers most commonly heard of are the 16-function controller and the 24-function controller. Each piece of equipment in the tunnel will occupy one function, whether or not they are used with each wash.

The amount of equipment in a tunnel will determine the size controller that is right for the wash. Most tunnel controllers today are expandable.

The ability to customize a controller’s number of outputs and inputs specifically to a site is another feature that will keep an owner from over-purchasing for their specific requirements. Many of the controllers today have the ability to customize by incrementally adding four outputs or inputs.

The entrance keypad contains the emergency stop button, the buttons to load the vehicle, the buttons to order specific wash packages or add-ons and the buttons to remotely enter generated wash package codes.

How the parts work
The entrance keypad is usually placed at the head of the tunnel. A wash is ordered at the entrance keypad and that message is transmitted to the controller.

The controller then waits for input from the gate switch and pulse switch to determine the length of the vehicle and conveyor speed.

After receiving input from these sensors, the controller turns on and off multiple relays at the proper time to create the wash that was ordered.

In recent years, the wash ordering process has been streamlined to ensure accuracy and protect against theft.

Some tunnels feature an automated entry system or auto-cashier, which allows the customer to select a wash, select add-on items and tender payment.

In this scenario, traffic may be controlled by a gate that is connected to the auto-cashier.

When the customer completes the wash order at the auto-cashier, the order is transmitted to the gate and tunnel controller to ensure that the appropriate car receives the appropriate wash.

This integrated setup reduces labor cost by automating the cashiering process.

It also reduces theft by ensuring that each vehicle receives only the level of wash for which they paid.

Using a tunnel controller
It is increasingly important that tunnel controllers are user friendly.

Many entrance keypads include a screen that displays messages to communicate with the operator, making controllers easier to program, adjust and diagnose.

In a traditional (centralized) tunnel, the microprocessor-powered controller and all outputs are contained in a single, waterproof box in the equipment room. While it is convenient to have all items in one place, wiring high voltage power and data from one end of the tunnel to the other is expensive.

Newer models have an option of distributing outputs near equipment. For example, a small waterproof box containing four outputs is placed directly at the solenoid or pump stations for ease of troubleshooting when using the on/off/auto toggle switch override.

The technician can test equipment with the relay’s override toggle switches at the equipment itself, saving him from having to run back and forth to the controller.

The small box is then connected via low voltage Category 5 wiring to the microprocessor controller.

Wiring costs are reduced (both hardware and labor) and testing/diagnostics are easier with output control near the equipment.

Using codes to sell
Tunnel controllers generally include the ability to handle codes at the tunnel entrance. This allows an owner to sell carwashes at the gas pump, fast lube, convenience store or auto-cashier (without gates).

A small code generation unit is connected to the device selling washes. When the car pulls around to the front of the wash, the attendant enters the code.

The controller communicates with the code generation unit to verify the code and order the appropriate wash. This again prevents theft and closes the audit loop.

Tunnel controllers are a vital part of every conveyor wash. Making the most of recent innovations can help reduce theft, increase efficiency and accuracy.

Trina Davis is the marketing manager of Integrated Services, Inc. (ISI) headquartered in Portland, OR. For more information, email

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