Back to the basics
It is important to understand that the photo-sensors used in door operators use invisible ULTRAVIOLET light. Contrary to popular belief, there is no steady beam between the two parts of the photo-sensor system.
Unlike a laser beam, the infrared light is rapidly pulsed. Typically called the TX & RX, the TX transmits the Infrared pulsing beam, and the RX counts the pulses.
We call this the pulse code, and it differs between products from different companies, so you usually cannot mix & match between brands. The pulse code can range from 5 pulses per second (pps) to 240 pps. At 240 pps, you would have an incredibly sensitive system, easily disturbed even by a moth or leaf. Many times, the TX will be designated by a green LED, and the RX by a red LED, but on some brands, an amber LED may be used.
Vibration in the track, loose sensor brackets, or photo-sensor beams not centered will eventually require a service call. An uncentered beam means that the units are a hair from being unaligned. You may see the TX LED illuminated, but the RX LED flashing. In this case, the beam is nearly misaligned. When the two sensors are communicating properly, both LEDs will be lit solid—not flashing. When the beam is not centered, any small twist in the wooden jamb can misalign it. Wood will absorb humidity, then can twist after drying out. It’s intermittent issues like this that can drive a person crazy! One day everything is fine, then the next day… chaos!
I recommend that you take a closer look at the RX LED and determine whether it is just flickering and very weakly illuminated. Moving either sensor will better center the beam and keep both LEDs steady. If you find the LED flashing faintly, it could be that the pulses from the TX are bouncing off the floor before reaching the RX. To troubleshoot the system, it may be necessary to extend the wire to one eye and bring it close to the other just for testing purposes. After alignment, you can move the sensor back slowly, ensuring the eyes stay illuminated and aligned. Another choice is to wire a test photo kit to the operator and verify the entire system. If you are installing the same operator consistently, then it would be helpful to carry a spare set of sensors mounted on a short board that you can wire to the operator for testing purposes.
Hey, what’s bumping?
Collisions with sensors can easily occur, from a bump with a bicycle, a motorbike, a lawnmower, or even a car itself. Sometimes, a homeowner will raise the sensors on the jamb to prevent them from being bumped, without having any idea that they have produced an unsafe condition. If you’re servicing doors, it is imperative that you check that both sensors are no higher than 6 inches off the floor, and if you find an error in the sensor height, you are obligated to place them at the correct height before leaving the home. If you ignore an unsafe condition and an injury occurs, believe me, you will be accused, sued, and implicated!
Don’t get your wires crossed
Wiring can easily get disturbed or severed.I’ve come across many strange things that have affected wiring, from a mouse or dog eating through it to a wire being torn accidentally from the sensor body.
It’s important to remember that any torn wire, open circuit, or short from a metal staple will causea fault, so you must verify that the wire is in good shape. This is impossible, however, in homes that are pre-wired, and you may need to string temporary wire to test the overall system.
One time, I discovered a broken circuit in the wall, and the homeowner demanded I fix the problem. Since I wasn’t ready to tear down all the drywall in the garage, I told the homeowner to take the issue to the builder. Because the new builder’s home warranty had expired, this led me to a dead end! I couldn’t leave the operator incomplete, so I returned days later and strung bell wire across the ceiling to the sensors. The guy wasn’t happy, but there really wasn’t any other choice except a totally expensive destruction of the garage. I ended up telling the guy to paint over the wire and forget about it.
Solar power
Our sun produces wavelengths of infrared light, which can bombard us all day. The infrared light will not affect the TX, but in most cases, it will affect the RX. It’s smart to check the sunlight in the morning and evening when it is on the horizon to see how it enters the garage. The best thing to do is install the TX on the side of the garage where you suspect sunlight may enter the garage. You can also use a piece of cardboard to shield the sensor if you witness a problem after the installation. Don’t ignore this potential issue, since solar infrared ultraviolet light WILL absolutely affect the RX pulse count.
If the pulse count is irregular, you will see nuisance reversals, or the system could prevent the door from closing!
Checking out the crosstalk
Crosstalk can occur when there are two operators side by side in the same garage, and two RX sensors pick up and count the pulses from one TX. The remedy for this is to install the two TX sensors back-to-back on the column between the two doors, shooting their pulses away from each other and toward only one RX sensor.
Other issues may arise
On homes that have a stem wall that is not higher than 8 inches above grade, you may find the wooden jamb does not go all the way to the floor. The installer will typically try to screw the sensor mounting bracket to the wood frame, but by doing so, they may install the sensor too high since the wood starts at 12 inches or higher from the floor. If the sensors are mounted too high, they no longer comply with UL 325, creating an unsafe condition.
In closing, let me enforce these rules: You must only install the sensors according to the operator instruction manual! At no time shall a sensor be installed higher than 6 inches off the floor.