Chamberlain garage door opener

[Bruce King]

If anyone has one of the newer Chamberlain or Liftmaster openers please check something and let me know.
As it’s closing, wave your foot across the center of the opening down where the safety beam is. Don’t do it near a sensor but right near the center and see if the door stops.

Here is why, mine won’t stop with a wave of a foot/leg near the center. The instructions say or show to use a box. Large objects will stop it. I have inspected no less than 8000 garage doors and never saw one with sensors fail to stop with a wave of my foot. I may not have done every one in the center though. Chamberlain has sent new sensors, nope. Now sending a circuit board. I suspect it’s a design error. Basically the beam is huge and harder to break than it should be.
Don’t test a door if you are not capable of getting out of the way. Thanks

[Dave Mills]

I just tested it with mine, and sticking my foot out there was seen, and the door reversed. I can't be sure what part of my foot or ankle the beam actually saw... This is a 12' wide door.

[Brian W Evans]

I have two Chamberlain belt drive openers, one installed maybe three years ago, and one installed last year. I have seen my dogs run through the beam without triggering the door reversal. I have also seen them trigger it, so I think it depends on how fast they are moving. For both dogs, the beam would be at leg level - not body level. It doesn't inspire a lot of confidence but the openers also have a pressure sensor that seems to work well.

[Eugene Dixon]

And my Liftmaster just rip the lift arm right of the center stile on my double car garage door on Sunday.

[Bruce King]

They don’t actually have a pressure sensor. They use an optical encoder to count revolutions of the motor shaft to detect when it slows down due to impacting an object. The force spike before it reverses can harm a child or pet. On newer openers they may be monitoring motor current to detect impact.

[Roger Feeley]

I had a hard time with sensors once and it turned out that the receiving side was in the sun part of the day. I switched them and it was fine. Could it be that your receiver is on the sunny side? If so, the receiver is seeing light from the sun when your foot is far away and thinks it's light from the sender.

[Stan Calow]

I had a hard time with sensors once and it turned out that the receiving side was in the sun part of the day. I switched them and it was fine. Could it be that your receiver is on the sunny side? If so, the receiver is seeing light from the sun when your foot is far away and thinks it's light from the sender.

I have the same situation.

[Bruce King]

I think sun on a certain one causes the door to not close.

[Myk Rian]

I mounted mine up on a rafter pointed at each other so I don't worry about it. No kids or animals to trigger it.

[Bruce King]

After many hours of work and Chamberlain sending me parts I had a brainstorm.
I thought, no way could they have messed up so many parts, I even got a whole new unit from them with the same problem. I put moving blankets on the floor to see if the paint had anything to do with it. Sure enough, it’s the floor paint, just plain ole garage floor paint, satin gray that previous owner put on about three years ago. Filed a report with the Safety Commission. Wait and see what Chamberlain does to keep someone from getting hurt.

[Brice Rogers]

So, Bruce King, what you are saying is that the transmitted beam is bouncing or reflecting off of the gray paint?

I would think that if the optical unit was properly designed that this shouldn't happen if the transmitter and the receiver are pointed directly at each other. (Check that). My guess is that there is a whole lot of excess "gain" in the receiver. That is, the "signal" that is reflecting off of the floor is sufficient to fool the receiver into thinking that it is receiving enough light that it believes that there is no blockage.

If you want to desensitize the optical unit, as either an experiment or as a potential "fix", I'd suggest (1) adding multiple layers of window screen in front of the receiver. Often times the transmitter has a tiny emitter and the receiver has a larger lens in front of it. So, putting the window screen or a coarse cloth/gauze will work better in front of the receiver. The layers of window screen will reduce the amount of light hitting the receiver. I suppose that it also might be possible to put something like wax paper between the two. (2) Another way to do this (based on your description) would be to buy a can of flat black paint and paint a stripe between the transmitter and receiver. That doesn't reduce the system "gain" but reduces the amount of light reflecting off of the gray floor (as well as the amount of light being received directly). And (3) you could take a tube (painted flat black inside) and attach one to receiver and one to the transmitter with each pointed at each other. The purpose of these two tubes is to only allow light (probably infrared which we can't see) to go directly from the transmitter to the receiver, and to block out light that is reflected off of the floor.

To me, it seems like a bad design or a "batch" manufacturing problem. (I am a degreed electronic engineer and have some experience with optical systems).

The trouble with requiring a box to block both the direct light and the reflected light is that you could have an animal only blocking the direct beam.