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I spy with my photo-eye

October 11, 2010
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In-bay automatic carwashes rely on sensors to control the carwash equipment. Without sensors, the wash computer would assume that every vehicle is the same length, height, and width.

It is important for in-bay owners to understand how to choose and maintain their sensors to ensure the highest performance in their wash bay.

Important applications

Applications for sensors include:

  • Starting the wash;
  • Measuring or profiling a vehicle;
  • Opening and closing the doors; or
  • Turning lights or indicators on and off.

Photoelectric, or photo-eye, sensors have become a preferred sensor in the carwash industry due to their touch-less performance and ease of use.

As with all electronic equipment, proper installation and regular maintenance will help to ensure uninterrupted performance from the photoelectric sensors.

Eye selection

When selecting a photoelectric sensor for an automatic carwash, consider how the sensor will be used.

Photoelectric sensor systems typically consist of:

  • An infrared transmitter;
  • An infrared receiver; and
  • In high-powered systems — an external amplifier.

For the simple detection of a vehicle, the photo-eyes are positioned on opposite sides of the carwash.

The transmitter photo-eye emits an infrared beam of light across the bay that is detected by the receiver photo-eye on the opposing side. When a vehicle interrupts the infrared beam, a signal is sent to the equipment to perform the desired function.

Mechanical treadle plates and loop detectors that are used to determine the position of the vehicle may also be replaced by photoelectric sensing systems.

It is best to mount one sensor higher than the other so that the sensors form a diagonal line to the ground.

This directs the beam through the area where the largest portion of the vehicle will pass and helps to reduce false signals.

Body basics

The body of the sensor should be durable and designed to withstand the harsh conditions of the wash. To meet the needs of the carwash environment, photoelectric sensor bodies are available in:

  • Plastic;
  • Nickel-plated brass; and
  • Stainless steel.

It is important to recognize that a residential garage door photo-eye lacks the proper sealing to be used in a professional carwash.

For best results, select a sensor with an IP67 rating. This rating indicates that the sensor is sealed in a way that will prevent the internal circuits from being damaged by water spray or submersion.

Sensing range and immunity to sunlight are also important features that affect performance.

A long-range infrared beam assists in penetrating cold-weather fog, steam, mist, and soap that are present while the wash is running. High LUX immunity to sunlight means that the sensors are less likely to be influenced by reflections from the sun.

Proper photo-eye maintenance

Photoelectric sensor maintenance is simple, requires very little time, and may be performed every one or two weeks.

The first routine maintenance task is to simply clean the front of both photo-eyes.

Next, verify the alignment of the photo-eyes using a length of string or wire long enough to pull in a line between the sensors. This line should be parallel with the sides of both sensors. Another idea is to use a laser pointer if one is available.

If you are using a set of photoelectric sensors that uses an external amplifier, some models offer built in alignment tools for the photo-eyes. The amplifier should be housed in a watertight enclosure box.

Periodically check to be sure that the seal on the enclosure box is still intact and that no water has penetrated into the interior of the box.

If quick-disconnect photo-eyes are used in the wash, be sure to apply dielectric grease inside the photo-eye's connector each time the sensor is replaced. This level of maintenance should extend the life of your photoelectric system.

Troubleshooting problems

When problems occur with the photoelectric sensors, first determine the nature of the problem.

  • Are they giving an intermittent output that flickers?
  • Do the sensors report an output all the time?
  • Is it difficult to break the beam between the photo-eyes?

Once you determine the nature of the problem, it is easier to isolate the cause.

1. Flickers: If there is a flickering output, check the alignment of the photo-eyes. Next, check to be sure that the strength of the photoelectric system is adjusted high enough.

On amplified systems, this setting is located on the amplifier, inside the watertight enclosure.

If the alignment of the photo-eyes and the system strength setting appears normal, check for corrosion at any points where either photo-eye's cable has been cut and spliced.

If you find corrosion, be sure to cut and reconnect the wires using a soldered connection and heat-shrink tubing. This will help to seal moisture from the connection.

Plastic twist-on wire connectors should never be used to make this connection.

If you still see flickering from the output of the photo-eyes, check to be sure that all of the necessary ground wires are connected to the ground. The wires from the photoelectric controls should never share the same conduit as the wires from any motor controls.

2. Constant output: A constant output may be caused by an obstruction in front of the photo-eyes. Be sure trash hasn't blown in front of the photo-eyes, blocking the infrared beam.

Alignment may also be an issue, but if the photo-eyes are out of alignment far enough to give a solid output signal, then this should be easily noticed.

Next, look closely at the face of the photo-eyes. Check for visible cracks or deep abrasions.

Even a sealed photo-eye can be rendered useless if a large crack forms on the face of the sensor, thereby allowing moisture to breach the internal circuits of the photo-eye.

3. Difficult to break: If it appears that the infrared beam between the photo-eyes is difficult to break check the sensitivity adjustment and the alignment of the photo-eyes.

When the intensity of the infrared beam is too strong, the beam may not be blocked as the vehicle passes. Reflections on the wet walls and floor will contribute to this problem.

Try turning the strength of the photoelectric system down. If this does not work, check the alignment of the photo-eyes.

Eye on the prize

Properly installing and maintaining photo-eyes at an automatic carwash site can enhance the speed and precision of service.

Trouble-free use of a photoelectric system is possible and can help increase the continuous high-performance of a site's carwash equipment.

Wayne Finley is the sales and marketing manager for Pantron Automation, Inc., a company offering a large selection of powerful photoelectric sensors for use in carwashes. He can be contacted at wayne@pantron.com.

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