From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Why do propane heaters draw so much electric current?
Date: Wed, 03 Jan 2001 12:02:43 -0500

Young wrote:

> My understanding of the Oxygen sensor is that it measures the oxygen content
> of the air by an electro chemical effect not partial pressure. Am I wrong? I
> hate that feeling<G>
>
> Frederick

You are.  The oxygen sensor consists of a specially designed pilot
light.  Under ordinary conditions, the pilot flame just barely is
retained on the burner mouth.  A bimetal-operated air shutter on the
air inlet compensates the pilot air mix for temperature to keep it
that way.  As the oxygen percentage drops, the flame gets longer and
tends to lift from the burner tip.  When the oxygen level in the
room drops to a dangerous level, the flame lifts off the burner and
goes out.  The thermocouple is placed to see only the pilot and not
the main burner.  When the pilot goes out, the main burner is
tripped a few seconds later when the thermocouple cools.  Easy,
simple, only one moving part, no moving part, and totally reliable.

Frankly I didn't believe that this would work when I first heard of
it.  I put my then-new unvented heater in a spare closet along with
an oxygen meter.  The thing tripped off at 16% oxygen.   The pilot
flame got longer and more transparent until it finally just lifted
off and went out.

John