IR cover

[williamwright]

I have safety sensors on my electric gates. They use IR beams. The covers of the transmit and receive units are one-piece plastic and have quite an elaborate shape. The cover of one unit was smashed by me reversing into it, so the dealer brought me another, and fitted it. The motor then declared that the beam was obstructed. We took the new cover off and the obstruction cleared. The new cover was completely opaque to both visible and IR light. It had been supplied as a spare part. We concluded that it was probably an early prototype that had somehow got in the manufacturer's stock of spares. Bill

[Andy Burns]

Do they have multiple versions with e.g. 810nm and 950nm LEDs?

[williamwright]

Dunno but the cover was absolutely opaque. I can't imagine any IR would get through it. I held it up to the sun and nothing got though.

Bill

[GB]

That's a poor test, I'm afraid. Your eyes can't see IR. Some substances that are transparent to visible light, eg glass, won't transmit IR.

[williamwright]

was these. The plastic of the 'eye' extends all the way to the sides under the aluminium cover. Bill

[SH]

Many Smartphones and digital cameras can actually "see" IR light.

I use thsi to check remote controls are operating by pointing the IR LED on the remote into the camera of the Smartphone or Digital camera. Press some buttons on the remote and the scren will show it as pinkish light.

Do this with known sources of 810 nm and 950 nm IR light and try again with the IR cover in the middle.

[alan_m]

If you want to make an IR filter for a digital camera the totally black bits at the start/end of a developed film were recommended - often stacked to two or three layers. You couldn't see through these.

Military IR cameras use Germanium as the lens! Thick black rubbish and rubble sacks are completely transparent for IR in those bands.

[alan_m]

More often these days blocked by a filter but sometimes the forward looking selfie camera will not have the filter.

[Harry Bloomfield, Esq.]

williamwright presented the following explanation :

Your eyes cannot see IR frequencies - put it in front of your phones camera and shine an IR remote control through it.

[williamwright]

But in reality anything that will transmit IR readily will show a bit of red light through it.

Bill

[GB]

Probably.

BUT! If this is a safety feature, the manufacturers may have gone to huge trouble to find a material that only transmits a narrow bandwidth covering the IR being transmitted. So, it doesn't get set off by some stray light.

If there's more than one IR LED that they use, it is just possible that you need to match the LED with the covers.

[Brian Gaff (Sofa]

Maybe you could cut a hole in it and glue a bit of normal IR transparent stuff off an old remote over the hole? Brian

[alan_m]

More likely to be a modulated IR light source with filters in the receiver to only accept the modulation frequency.

[alan_m]

Moisture/condensation in the broken unit? Water is a good attenuator for IR and a cover could add more attenuation of the signal.