Date: Mon, 13 Feb 2006 02:31:39 -0600
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: volt/ohm meters
In-Reply-To: <6da579340602122120q65133947ha6d6184ce958ca11@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I've got an analog meter that is still in the box - 36 years old - looks
and works like new. Have no intention of replacing it. Don't own a
digital, but thee have been a few times that I wish I did, but I managed.
Latest pressure for me to get a digital meter is something I'm working
on. I'm a potter, and I'm gearing up a small gas-fired kiln. Most kilns
run with an oxidation state inside - ie, plenty of oxygen for complete
combustion. My objective is to operate the kiln with an internal
atmosphere that is in a reduction state - that is, there is insufficient
oxygen present in the internal atmosphere of the kiln for full
combustion of the gas going into the kiln. This will force the flame to
seek oxygen from other sources - from the clay in the pots, from the
glazes on the clay pots. This results in some extraordinary colors. One
of the big bugaboos in achieving this is how to monitor - and control -
the internal atmosphere to keep it in reduction. Control of the
atmosphere is by way of fuel and air adjustments done manually. But one
needs to be able to tell what the atmosphere actually is after
adjustments. There are commercial instruments for monitoring this but
they are quit expensive - involving a digital meter, a platinum tip
probe encapsulating a zirconium crystal. - and costing $600 and up. And
the whole shebang - except for the meter - gets stuck through the
sidewall of the kiln so the tip is inside. Well, as it turns out, the
tip of the Vanagon O2 sensor(as are others) is made the same way - and
by sticking that sensor through the thin exhaust stack of the kiln just
outside of the exhaust port in the top of the kiln, the O2 sensor can
be made to produce a voltage - positive or negative - depending on how
much oxygen is present in the exhaust gas - and the voltage can be read
on a digital meter and correlated to a temperature chart, AND the amount
of negative or positive voltage can be correlated to another chart to
give the degree of oxidation or reduction taking place in the kiln.
So, taking the ol' O2 sensor application and putting it somewhere else
is going to save me a bundle. Brand new O2 sensor - $40 or less. Decent
digital meter - $50 or less, vs the commercial O2 setup for kilns at
$600 and up. Big difference.
Will post how it goes.
John Rodgers
88 GL Driver
John Bange wrote:
>> I am thinking of buying a volt/ohm meter in the near future for work on
>>the van and around the house. Does anyone have a recomendation on a brand
>>and or model. Ido not need pro cababilities.
>>
>>
>
>
>Cheap digital meters are OK, but I almost think you're better off with a
>cheap analog. I have a trashy $6 Harbor Freight digital I use for piddling
>around, but I also have an old analog tucked in the back of the toolbox for
>when the battery goes out on the digital. Those cheap crap meters can get
>pretty erratic when the 9V battery gets to under 8V and they generally give
>you no warning other than the readings getting funny. Old guys who swear by
>analog meters do have a valid point. For work I have a fairly expensive
>Fluke digital that is in most ways as good as an analog, but that's probably
>overkill for home and shadetree mechanic work.
>
>--
>John Bange
>'90 Vanagon - "Geldsauger"
>
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