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From: Paul Honigmann
Subject: Re: Furnace oil tank safety alarm
Date: Sun, 8 Sep 2002 15:40:23 +0100
Organization: Nysalor Seminary for Unrepentant Riddlers
Reply-To: Paul Honigmann
NNTP-Posting-Date: Sun, 8 Sep 2002 14:59:05 +0000 (UTC)
User-Agent: Turnpike/6.00-S ()
>So you would measure evaporated CH compounds?
Yes. You can use infrared (spectroscopy) tuned to C-H bonds, or
pellistor techniques which react to any vapour which burns. Or
semiconductor sensors, but personally I don't like those much because
they react to anything, including ambient temperature and humidity
changes, so you don't know if it's a real alarm or not.
>The sensitivity has to be way up there for it to react at the begining of a
>small leak, but still be able to discriminate other small gas leaks such a
>humans dispensing methane...;P
Those will get diluted to parts per billion 8)
Infrared will show up ppm and pellistors (which are rather old fashioned
but cheap, and they work) will show up levels of around 0.05%. Since the
flammable level of most gases is around 1 to 5% by volume in air, the
obvious choice would be to use a cheap pellistor.
The catch is that such a system is going to set you back... I dunno... a
couple of thousand Euros I guess. Because it needs to trigger an alarm
somewhere, so you need a PLC, etc etc. All the bits add up. An amateur
could knock something together much cheaper, but the professional
companies need to recover costs spent proving these things are safe. You
aren't allowed to sell equipment for hazardous areas (where there is
potentially flammable vapour) without third party testing and stuff and
it's all very expensive.
Come to think of it, we recently developed something called "FlamSafe"
which is a cut price system specifically for this kind of application,
so you might want to check that on the URL below.
Gosh this Sales stuff is hard. I'd better stick to engineering. You
don't need communication skills for that.
>> I'd just like to point out that the company I work for makes leak
>> detector type things* for flammable gases - check out www.crowcon.com
>> Paul Honigmann
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