Bob Dolph Answers Questions on Contacts, IR Dangers

Q: I have had a problem at a customer’s house with sticky reed contacts.  When was testing a system, I noticed that one of the magnetic reed contacts would not open the circuit when a door was opened.  I tapped on the contact and it appears to be working now.  Should I replace it?

A:  It would be wise to replace it.  This is a common indication of a nearby strike from lightning.  The surge possibly welded the tips of the read closed.  Your tapping was just enough to free the reed contacts.  There is a good chance that they are damaged and will give you poor performance down the road.  The harder you have to tap to free them the more they are damaged.

Q:  I have heard that infrared (IR) illumination for CCTV systems can be dangerous to a person’s eyes.  Is this statement true?

A:  Yes and no.  Let me explain.  But first, let me read you a quote from Extreme CCTV white paper on IR Illumination safety:

“Throughout history people have been exposed to high levels of infrared radiation, in the making of steel or glass, simply being out in strong sunlight, in fact anywhere close to a hot object. Infrared gives a heating effect, which we sometimes use to keep us warm, but too much on the skin can cause blistering. Industry is aware of the dangers of high intensity IR radiation and the risks and effects of over exposure to it are well known.

“Bright natural light which contains infrared causes the eye to blink, the iris to contract and the viewer to look away. These normal defense mechanisms do not happen when the visible part of the light has been removed. The eyes are more sensitive than the skin, and over-exposure for long periods may give rise to retinal damage and cataracts. These are the hazards of over-exposure to IR.”

All this being said, one should not look for long periods of time and at a close range at an IR illuminator.  Most manufacturers have application guidelines for these devices and it is recommended that you follow them for both your customers and your installers and technicians.

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