Robert on mon 21 jan 08
I think the most valuable use of a pyrometer, particularly a digital
pyrometer, is the ability to determine atmosphere quite accurately by
timing the rate of temperature increase. The greatest rate of
temperature rise will be at the stoichiometric balance, or neutral
atmosphere, just enough air to burn all the fuel introduced, not too
much to cool, or to little to produce reduction. I like to find a short
time, 1-3 min. that I can easily multiply into a rate per hour. The
rate per hour is helpful, but the key is the relative increase
adjusted by changing the damper setting. Push it in a little, rate
starts climbing, it had a little more than it needed. Push it in a
little more, give it time to breath, check again. Rate of increase goes
down, a little, adjust to taste.... Very useful tool. pays for itself
quickly, if only in fuel efficiency let alone understanding where your
kiln is, in terms of atmosphere, at any given point. Cones are about
fusion. Not combustion efficiency or atmosphere.
Take care
Robert
Wil Morris wrote:
>
> As for Pyrometers... The main reason why I was considering one is so that
> I dont ramp up or cool down too fast. Of course I would use cones to
> determine finished climb. I guess I could use a lot of cones to watch
> climb. I just hear all of this talk about soaking and holding and Im a
> little unsure how to do this without a pyrometer.
>
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Larry Kruzan on mon 21 jan 08
Hurray! A pottery question!!!!!
A Pyrometer reads a small voltage generated by the thermocouple, the hotter the temp - the more voltage is generated and translates the reading into numbers we understand as degrees. So........
Purchase a type K thermocouple, terminal block, and wire from one of the normal suppliers, a skutt type "k" T/C is around $12 not sure about the wire and block. Find a digital multimeter for a few bucks at the junk shop or radio shack. Assemble a cone pack with cones for each of your target temps, 012,04,6,8,9,10 so on. Hook up the thermocouple to the multimeter. Set Multimeter to the millivolt scale. Fire up the kiln and watch the cone pack. Note and record the reading of the mulitmeter as each cone drops. Your calibration is finished. You now have a digital pyrometer.
If the meter shows negative numbers or nothing - reverse the leads. Depending on the meter it may have a couple settings for millivolts.
Test this since I have not done it this way buit it should work.
Larry
----- Original Message -----
From: Wil Morris
Date: Monday, January 21, 2008 16:18
Subject: [CLAYART] Re : cone vs. temp question
To: CLAYART@LSV.CERAMICS.ORG
> A few people have asked for pictures of the home-depot
> burner. Maggie
> Jones was nice enough to give me links to her server so I can
> post some
> images.
> It's nothing fancy, but here you go.
>
> http://maggiejones.20fr.com/WilMorrisburner1.jpg
> http://maggiejones.20fr.com/WilMorrisburner2.jpg
> http://maggiejones.20fr.com/WilMorrisburner3.jpg
>
> It's just an old Duncan Kiln that one of the switches blew on.
> It cost way
> too much to fix and replace the elements so I thought, 'Why not?'
>
> I think I made the vent a little too big. I cut a hole in the
> center 4"
> (~100mm) squared. So I just baffled it with kiln shelves
> till I saw no
> smoke or flame. My little knowledge of gas assumes that
> this will be the
> diffence between Ox and Reduction. A broken triangular
> shelf on top made
> a nice adjustment piece.
> I'm not sure if I liked the flame very much. The nossle
> has 6 holes
> instead of one. Each hole is a little less than 1mm. This seems
> like an
> overkill. Low flame is just a yellow fire. At high the
> flame almost
> dissapears. The plus side (I think) is that the flame is
> dispersed in a
> circular pattern on the bottom of the kiln. My bottom pieces overfired
> (next time Ill put a cone down there too) Im gona get bricks
> instead of
> using shelves to shield the flame. The nossle can
> come off with a wrench
> so I was thinking about looking into changing it to smaller diameter.
>
> As for Pyrometers... The main reason why I was considering one
> is so that
> I dont ramp up or cool down too fast. Of course I would use
> cones to
> determine finished climb. I guess I could use a lot of
> cones to watch
> climb. I just hear all of this talk about soaking and
> holding and Im a
> little unsure how to do this without a pyrometer.
>
> ______________________________________________________________________________
> Clayart members may send postings to:
> clayart@lsv.ceramics.org
> You may look at the archives for the list, post messages, or
> change your
> subscription settings here: http://www.acers.org/cic/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots2@visi.com
Tim See on tue 22 jan 08
Im sure this has been said other places but you cannot calibrate a pyrometer with cones/ or a multi-
meter. cones measure heat work therefore measure time along with temp to get a more accurate but
not calibrated multi meter conversation you would need to heat the kiln up at a rate that was
specified by the cone tables are given in a few books on how much increase per hour to reach a cone
at the approximate temp of the kiln at a cone bend. then you have to be really good at placing cones
and knowing when it is truly down not just soft. A multi meter wood be good at telling you the
direction of the kiln if its going up or down.
Doug Trott on tue 22 jan 08
Robert -
That's an interesting observation, though I expect it's most accurate with =
a gas kiln. I'm thinking that with a wood kiln, a couple other factors com=
e into play that would affect the accuracy of that calculation. The first =
is just the location of the pyrometer along the path of the draft - it's di=
stance from the firebox. The second is the draft itself - if I slow it dow=
n with dampers I'll affect the rate of temperature change, although there c=
ould be impact to the environment too.
Have you (or anyone) tried this with a wood kiln?
Doug
> Date: Mon, 21 Jan 2008 19:04:42 -0800
> From: nativeclay@GMAIL.COM
> Subject: Re: Re : cone vs. temp question
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> I think the most valuable use of a pyrometer, particularly a digital
> pyrometer, is the ability to determine atmosphere quite accurately by
> timing the rate of temperature increase. ...=
Ivor and Olive Lewis on tue 22 jan 08
Dear Larry Kruzan,=20
If you check in the Electronic Supply Catalogues you will find that many =
multimeters are able to give you direct temperature readings up to 1300 =
deg C and come supplied with K type thermocouples. I use two. But I also =
have an industrial grade K probe with a 12 inch sheath as well as short =
probes..
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Robert on tue 22 jan 08
Doug,
I think you are correct and I should have noted it in my last post. The
wood stoking cycle varies too much between reduction, neutral and
oxidizing to use this method as an accurate gauge. Though, perhaps with
a bourrey, having a longer stoking cycle, you might get a window of
viable data in the middle of the charge. It is mainly appropriate for
gas or oil firings.
Robert
Doug Trott wrote:
> Robert -
>
> That's an interesting observation, though I expect it's most accurate with a gas kiln. I'm thinking that with a wood kiln, a couple other factors come into play that would affect the accuracy of that calculation. The first is just the location of the pyrometer along the path of the draft - it's distance from the firebox. The second is the draft itself - if I slow it down with dampers I'll affect the rate of temperature change, although there could be impact to the environment too.
>
> Have you (or anyone) tried this with a wood kiln?
>
> Doug
>
>
>> Date: Mon, 21 Jan 2008 19:04:42 -0800
>> From: nativeclay@GMAIL.COM
>> Subject: Re: Re : cone vs. temp question
>> To: CLAYART@LSV.CERAMICS.ORG
>>
>> I think the most valuable use of a pyrometer, particularly a digital
>> pyrometer, is the ability to determine atmosphere quite accurately by
>> timing the rate of temperature increase. ...
>>
> ______________________________________________________________________________
> Clayart members may send postings to: clayart@lsv.ceramics.org
>
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com
>
>
Ivor and Olive Lewis on wed 23 jan 08
Dear Robert,
<pyrometer, is the ability to determine atmosphere quite accurately by =
timing the rate of temperature increase.
The greatest rate of temperature rise will be at the stoichiometric =
balance, or neutral
atmosphere, just enough air to burn all the fuel introduced, not too =
much to cool, or to little to produce reduction.>>
Are you sure about this ? As I see it, as you move away from a =
stoichiometric mixture, regardless of excess air or fuel, the rate of =
temperature increase will decline. So it is not a way of discriminating =
between an oxidising or reducing atmospheres. In other word it cannot =
act as an Oxy-Probe.
What a determination of the heating rate can tell you is efficiency of =
fuel use. Perhaps that is what you intended?
Are you aware that the chemistry given to us in our pottery textbooks to =
describe combustion of carbonaceous fuels may disregard other chemical =
reactions that can occur to the products of combustion before they exit =
from the kiln?=20
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Robert on wed 23 jan 08
Ivor
I think we are saying the same thing. The rate of temperature increase
will be greatest with a stoichiometric mixture. The rate will decrease
in either direction. Open the flue, more air, temperature rate
decreases, you are moving into an oxidizing condition. Close the flue,
less air, temperature rate decrease, you are moving into a reducing
condition. At any fixed gas setting and temperature one can find, with
a few observations and flue adjustments where the greatest rate occurs
and adjust for atmosphere, or, when desired, the maximum or desired
temperature rise. This may require readjusting the gas if a given
setting produces other that the desired rise at a given setting, and
readjusting the flue, with observation, to the stoichiometric mix. Of
course this shifts throughout the firing as the combustion efficiency
(or rather the rate of oxidation of the fuel) increases with temperature
throughout the firing. I learned this technique on the list several
years ago. I believe it was a professor , perhaps from Texas, (can
anyone help here?) who either posted or was referenced on the list. I
was perhaps overstating the matter to say it accurately determines the
atmosphere, it really provides a reference point, but is practically
accurate for determine the neutral or stoichiometric balance. While it
may not take into account all the chemical processes taking place, it is
a very useful method which has served me well.
Take care,
Robert
Ivor and Olive Lewis wrote:
> Dear Robert,
>
> <>
> The greatest rate of temperature rise will be at the stoichiometric balance, or neutral
> atmosphere, just enough air to burn all the fuel introduced, not too much to cool, or to little to produce reduction.>>
>
> Are you sure about this ? As I see it, as you move away from a stoichiometric mixture, regardless of excess air or fuel, the rate of temperature increase will decline. So it is not a way of discriminating between an oxidising or reducing atmospheres. In other word it cannot act as an Oxy-Probe.
>
>
>
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