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robbin
Mod
join:2000-09-21
Leander, TX

1 edit

robbin to lutful

Mod

to lutful

Re: Garage door problem

said by lutful:

You can verify from the shadow cast by the stick figure that it is quite impossible "for the sun to hit one sensor in the morning and the other in the afternoon" ... if you define "hit" as a reasonably small acute angle between sun-sensor-source

We aren't debating whether it can do it in a single day, but whether at some point in the year it can affect a sensor on one side of the door and at another point in the year it can affect a sensor on the other side. You are of the opinion that it would be impossible and I think it is possible with the likelyhood greater as you move towards the equator but probably more likely towards the tropical latitudes and diminishing in the equatorial region.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by robbin:

We aren't debating whether it can do it in a single day, but whether at some point in the year it can affect a sensor on one side of the door and at another point in the year it can affect a sensor on the other side.


Try early morning on June 21 for one side and late afternoon on Dec 21 for other side. Or any other two date pairs when you think the worst case scenario might happen.

Make reasonable assumptions for the location of the sensor (like x=6 inches from garage opening ; y=1 inches towards the side wall ; and z = 6 inches from floor ) and sensor acceptance angle (like 11.25 degrees for a pathetic design).
said by robbin:

You are of the opinion that it would be impossible and I think it is very possible.

If this was just a matter of personal opinion, I would have stopped arguing long ago.

garys_2k
Premium Member
join:2004-05-07
Farmington, MI

garys_2k to robbin

Premium Member

to robbin
said by robbin:

said by lutful:

You can verify from the shadow cast by the stick figure that it is quite impossible "for the sun to hit one sensor in the morning and the other in the afternoon" ... if you define "hit" as a reasonably small acute angle between sun-sensor-source

We aren't debating whether it can do it in a single day, but whether at some point in the year it can affect a sensor on one side of the door and at another point in the year it can affect a sensor on the other side. You are of the opinion that it would be impossible and I think it is possible with the likelyhood greater as you move towards the equator but probably more likely towards the tropical latitudes and diminishing in the equatorial region.

Actually, it's more likely the further from the equator you go. Think "midnight sun." A north-facing opening, with one inside wall facing east and the other west will have some days around the equinoxes where light will fall (at a low angle to perpindicular) on one wall in the morning and (on a different day) on the other in the evening.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by garys_2k:

... north-facing opening, with one inside wall facing east and the other west ...

I understand what you are thinking, but the during the short time when the sun can hit an east-west oriented sensor at a narrow enough angle ... it will probably be blocked by trees and other homes.

Proper installations put the sensor about 6 inches from garage opening and at least 1 inch back towards the wall. That tiny offset will make the (maximum 15 degree wide) viewing cone stay completely within the garage. Properly designed sensors should reject sun-equivalent brightness between 15-20 degrees which also imply rejecting sun interference at higher angles.

The only problem left unconsidered is reflection from a very glossy floor or object coming into the sensor below 20 degrees.

garys_2k
Premium Member
join:2004-05-07
Farmington, MI

garys_2k

Premium Member

said by lutful:

said by garys_2k:

... north-facing opening, with one inside wall facing east and the other west ...

I understand what you are thinking, but the during the short time when the sun can hit an east-west oriented sensor at a narrow enough angle ... it will probably be blocked by trees and other homes.

Maybe, or maybe not. Remember that there's a big, wide driveway right outside that door and then a yard. Maybe plantings will block the sun but in a lot of cases that won't be the case.
said by lutful:

Proper installations put the sensor about 6 inches from garage opening and at least 1 inch back towards the wall. That tiny offset will make the (maximum 15 degree wide) viewing cone stay completely within the garage. Properly designed sensors should reject sun-equivalent brightness between 15-20 degrees which also imply rejecting sun interference at higher angles.

So, we have a 16' wide door, that is 192" from side to side. We mount the sensor 6" inside the door and an inch further back, placing it 193" from the other side and 6" back. That means the tangent of the lowest possible angle that can cause sunlight to shine onto the eye is 6/193 = 0.0311, the arctangent being 1.78 degrees. That would be well within any reasonable acceptance cone for the receiver.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

Click for full size
said by garys_2k:

lowest possible angle that can cause sunlight to shine onto the eye is 6/193 = 0.0311, the arctangent being 1.78 degrees. That would be well within any reasonable acceptance cone for the receiver.

I drew a sensor located 6 inches in from garage opening and 1 inch back towards the wall. Imagine the sun is hitting those blue lines ... and they are NOT transparent.

The cylindrical pendulum used for the compliance test is less than 2 inches in diameter and placed 12 inches from sensor in beam path. If either the beam or the sensor angle was wider than certain values, and the transmitter was 200 inches away ... the pendulum test would fail because of diffraction. Any takers for those calculations?

robbin
Mod
join:2000-09-21
Leander, TX

robbin

Mod

Why are you referencing a test to check the response to an object moving through the beam when the discussion is in regards to sunlight affecting the sensor?
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by robbin:

Why are you referencing a test to check the response to an object moving through the beam when the discussion is in regards to sunlight affecting the sensor?

54067323 See Profile has been insisting that " garage door photo beams have a wider beam than security photo beams, which is why garage door photo beams can be swamped a lot easier then the ones designed for security." and the pendulum test debunks both of those theories.

Let me summarize what I tried to point out so far:

Any modern garage door sensor system, whose design has actually passed both the flood lamp test and the pendulum test, and which has been installed properly, with the sensor off-set mounted on the less sunny side and aimed at the transmitter with high precision, will NOT be affected by sunlight.

Of course, I realize that is happening in some installs, but there is sufficient information in this thread and those links to fix the root cause which is more likely to be a poor installation and less likely to be a non-compliant sensor system.

I promise not to reply to any more counter arguments since so many people are willing to believe them.

LazMan
Premium Member
join:2003-03-26
Beverly Hills, CA

LazMan

Premium Member