Bob;
Those are cadmium sulfide cells. They change resistance with light.
There is a similar one, cadmium selenide, which is also used but has a
bit different response.
The problem with these cells is that they respond to almost any type of
light-- including sunlight-- so they must be carefully shielded but
still be able to "see" the zone you are trying to protect.
The more sophisticated optical detectors sense either short ultraviolet
or long infrared wavelengths and respond to a flame flicker frequency
instead of steady ambient light.
Any type of detector, even if it isn't a very sophisticated one is
better than no detector at all, providing that:
1. You recognize that it isn't 100% reliable and take appropriate other
precautions and
2. The detector doesn't generate false alarms so often that it is
ignored when it does give an indication.
Regards, Neil Tucson, AZ
-----Original Message-----
From: owner-land-speed@autox.team.net
[mailto:owner-land-speed@autox.team.net] On Behalf Of Bob Jepson
Sent: Monday, March 15, 2004 6:42 PM
To: Land Speed
Subject: Fire Safety
For what it's worth, up here in New England alot of us folks use #2
oil-fired
burners to get our houses warm. As part of the safety design burners use
a
"Cad Cell" to optically detect flame such that the system will shut down
if
the light of the flame is not present. This puny pigtailed device has
600-800
ohms when it's seeing light, over 10K ohms when it sees dark. I've never
bought one but it couldn't cost more than a couple of bucks.
No doubt it would work well in a closed compartment for fire detection
on a
budget.
I'd be happy to get a few and send 'em along if anyone wanted to play
with the
idea....BJ in the Bean, where safety comes first!
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