My garage door keeps opening because (as I believe) the eyes "think" a
person is standing under the door as it comes down.
I've tried removing the sensors and lining them directly to avoid any
vibration the moving of the door may cause, however, that doesn't appear to
have fixed the problem.
There are two wires going to each sensor that I've measured; one wire is
ground and the other is +12v.
Can anyone tell me how these sensors tell the system a person is standing
under the door?
Any assistance will be appreciated.
Thanks in advance.
Several different systems are used. The most common is a modulated infra
red light beam sent from one "sensor" (actually just a transmitter) to
the other (actually a receiver). The signal is modulated so that the
receiver will not recognise other sources of IR, eg ambient lighting.
When someone stands between the transmitter and receiver, the signal is
blocked and the sensor triggers the "obstacle" alarm.
I am assuming that it did work once, but has now become unreliable. And
that there are no other symptoms - eg interference on the TV or radio at
the time these detections happen.
Whilst there are various tests that you can do, these do require
specialised test equipment. eg to measure the light output from the
transmitter and the sensitivity of the receiver. It may be that the
units are fine - but the system is, say, responding to electrical noise
on the power lines. There may be dirt or condensation between the outer
lens and the actual emitter or receiver element within the enclosure.
However, if nothing else has changed, the odds are that either the
transmitter output has fallen, say because of an occluded lens, or the
receiver sensitivity has fallen - for a similar reason. Or both.
I'm afraid that all I can suggest, if you don't want to call in a
professional, is to replace the two "sensors" with new units. It may not
fix the problem. You may be replacing both units, although only one is
faulty. You could always do it one at a time... They do need to be the
same part numbers as the original, from the same manufacturer. Of course
if the problem isn't with the "sensors" - you have gambled the cost of
new ones and lost.
What you should see is that the voltage on one "sensor" stays constant -
what you are measuring is the fixed voltage fed to the transmitter.
Whereas the voltage on the other unit changes (possibly drops to near
zero) when something obstructs the line of sight between units. However,
depending on the design, it may drop and rise again too quickly for you
to see without suitable test equipment.
It isn't only money that you are gambling though:
Bearing in mind that these sensors are a safety device intended to stop
people or pets getting hurt - I would suggest calling in the
professionals. Luckily it does seem to be failing safe at the moment -
detecting an obstruction when there is none. However, this could change
to not detecting an obstruction when there is one... DIY repairs to
safety equipment is not only risky - it can also leave you exposed to
compensation claims, if there is an injury. It can also lead to a great
deal of heart-ache, for a very long time...
Is there a backup system based on the usage in in older garage door
openers?. Measurement of motor current or some mechanical switch set to
operate at a given force detects higher than normal loads and treats them as
blockages. I have an older system (without sensors) which effectively (and
adjustably) limits the closing force and reverses the motor if this is
exceeded. This is set so that the force is not dangerous to someone and
manually holding the door causes re-opening. Check the door rollers and
tracks for binding or some object that may have somehow been lodged in the
Have you checked the downforce adjustment? Does the door move freely
with the opener disconnected?
This really does not sound like a photocel problem. It is more like a
mis adjusted down force screw or a bind in the door
Steve, Not to tag on, but I have an occasional problem in the morning with
our garage door opener which is usually seasonal as when the temperature
drops in the fall and winter. I usually begin by clearing any dust or
leaves in front of the sensor lenses. If that fails to fix the problem then
the door must be manually closed. It usually works when we return from
work. I'm beginning to think based on Sue's comments below that there may
be some condensation within the sensor due to the temperature drop but I'm
not an electrician.