Dennis Gerasimov on sat 10 oct 09
Hello fellow Clayarters,
It turns out that the pyrometer that I have is way off (judging from the
cones and other known temperature references), and in need of being
recalibrated. I tried googling up the procedure but came up mostly with
uber expensive optical pyrometer calibration apparatus. Anyone knows how
to calibrate the pyrometer, preferably without sending it off and paying
lots of $$ for the service?
All I need is a good temperature reference. For low temp digital
thermometers I always used thawing ice slurry and boiling water - these
are very reliably at 0 and 100 C. Anyone knows such reference in the
range appropriate for the K type thermocouple pyrometer?
If not, then perhaps, how do I find a service to do this in Baltimore or
DC area (so that I do not have to ship it around)?
Thanks!
Dennis
Larry Kruzan on sat 10 oct 09
Hi Dennis,
Are you seeing a difference due to the ware (and cones) lagging the
atmospheric temp? My pyrometer is always 50 degrees or so behind the cones
at the top temp but close up to 1600 f or so.
Larry Kruzan
Lost Creek Pottery
www.lostcreekpottery.com
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Dennis
Gerasimov
Sent: Saturday, October 10, 2009 7:39 AM
To: Clayart@LSV.CERAMICS.ORG
Subject: How to calibrate a pyrometer?
Hello fellow Clayarters,
It turns out that the pyrometer that I have is way off (judging from the
cones and other known temperature references), and in need of being
recalibrated. I tried googling up the procedure but came up mostly with
uber expensive optical pyrometer calibration apparatus. Anyone knows how
to calibrate the pyrometer, preferably without sending it off and paying
lots of $$ for the service?
All I need is a good temperature reference. For low temp digital
thermometers I always used thawing ice slurry and boiling water - these
are very reliably at 0 and 100 C. Anyone knows such reference in the
range appropriate for the K type thermocouple pyrometer?
If not, then perhaps, how do I find a service to do this in Baltimore or
DC area (so that I do not have to ship it around)?
Thanks!
Dennis
Michael Wendt on sat 10 oct 09
Dennis,
If the thermocouple is old, I would buy a new thermocouple
first. As they age, the reading drifts.
Second, point though...
Why worry about calibration?
If your cone 5 bends at some temperature T1 that is either
lower or higher than the cone chart says, make note of it
and check the cones frequently as that temperature is
approached.
If the actual temperature is important to you for some other
reason, get the manufacturer's directions for calibration.
It usually consists of adjusting the resistance in the
circuit either by turning a tiny potentiometer or adding or
subtracting small resistors.
Digitals usually have an adjustment mode for thermocouple
offset to compensate for incorrect temperature readings.
Regards,
Michael Wendt
Dennis wrote:
Hello fellow Clayarters,
It turns out that the pyrometer that I have is way off
(judging from the
cones and other known temperature references), and in need
of being
recalibrated. I tried googling up the procedure but came up
mostly with
uber expensive optical pyrometer calibration apparatus.
Anyone knows how
to calibrate the pyrometer, preferably without sending it
off and paying
lots of $$ for the service?
All I need is a good temperature reference. For low temp
digital
thermometers I always used thawing ice slurry and boiling
water - these
are very reliably at 0 and 100 C. Anyone knows such
reference in the
range appropriate for the K type thermocouple pyrometer?
If not, then perhaps, how do I find a service to do this in
Baltimore or
DC area (so that I do not have to ship it around)?
Thanks!
Dennis
Bruce Girrell on sat 10 oct 09
Dennis,
The first question I would ask is "why calibrate it?" I know this may sound=
=3D
odd, but until you need to compare your readings to someone else's, calibr=
=3D
ation doesn't matter much. As long as your readings are repeatable, then yo=
=3D
u probably have all that you need. It doesn't really matter what the absolu=
=3D
te temperature reads all that much. We fire by cones for high temps and by =
=3D
sight for raku temps. The pyrometer alerts us to when we should be paying a=
=3D
ttention to our other measurements and, if sufficiently sensitive, alerts t=
=3D
o the relative change in temperature, which can be important after changing=
=3D
a damper or air shutter setting. Neither requires an _accurate_ temperatur=
=3D
e. What we actually need most of the time is repeatability (so that the sam=
=3D
e thing can be done from firing to firing) and precision (so that relativel=
=3D
y small changes can be detected).
But I doubt that is a very satisfying answer. Before you go further into th=
=3D
e calibration direction, first make sure that everything other than the pyr=
=3D
ometer is up to snuff.=3D20
First, check the connections between your thermocouple and your thermocoupl=
=3D
e wire. A tiny bit of corrosion there can make a big difference. Clean ever=
=3D
ything up with fine sandpaper or other fine abrasive. Make sure there is no=
=3D
grit left in the connection when you are done.=3D20
Secondly, you _did_ use the proper thermocouple wire, didn't you? If you di=
=3D
d not use the proper type of thermocouple wire, then you built extra thermo=
=3D
couples (at each connection) into the system. These little additional therm=
=3D
ocouples can throw the calibration off quite a bit.
Next, how old is the thermocouple? I'm guessing that it is a type K thermoc=
=3D
ouple. If so and if it has seen a good number of firings, one easy - and no=
=3D
t all that costly - things to do is replace the thermocouple.=3D20
Once you are sure that all parts of your system, other then the pyrometer, =
=3D
are good, check your temperatures again. Perhaps you can find another potte=
=3D
r in your area who has a pyrometer that you can trust and borrow that one t=
=3D
o compare with. As far as actually making an adjustment of the meter - well=
=3D
, you got me on that one. I never tried it myself. I have a Fluke pyrometer=
=3D
with type K thermocouples and an oxyprobe with type R thermocouple. The tw=
=3D
o instruments agree quite well, so I have never had to make any adjustment.
Here is a kiln log from a recent firing.=3D20
http://farm3.static.flickr.com/2548/3998368030_a82d5b5643_o.jpg
The orange curve is a type K thermocouple in the side wall of the kiln and =
=3D
the maroon is a type R at the center of the kiln arch. The lower, dark blue=
=3D
, curve is the temperature at the base of my stack and the other curves rep=
=3D
resent damper setting and gas pressure. The main thing to note is the good =
=3D
agreement between the orange and maroon curves.
Bruce Girrell=3D
Fredrick Paget on sat 10 oct 09
> Anyone knows how
>to calibrate the pyrometer, preferably without sending it off and paying
>lots of $$ for the service?
>
>
>Dennis
It is usually done by hooking up a pyrometer calibrator to the
pyrometer and applying a calibration signal of the appropriate
microvolts input to read the temperature.
There are published tables of type K thermocouple 's microvolt vs.
temperature. So it is merely apply the microvolts for a certain
temperature and see if the reading is correct on the pyrometer.
Problem is that these calibration instruments are not cheap. If the
pyrometer is digital the calibration is built into tne software and
the chip and there is not much you can do about it.
Old type K 's that have been used a lot get bad and do not put out
the established published signal. Maybe you need a new one.
--
Fred
Twin Dragon Studio
Mill Valley, CA, USA
Steve Mills on sun 11 oct 09
Dennis,
Mechanical Pyrometers rarely need re-calibrating, Digital never in my exper=
ience.
It is probably the thermocouple that is "way off"; they have a pretty short=
"accurate" life, some shorter than others.
Type R or S: 5 to 8 years, they are the longest survivors, Type N is 4 to 5=
years, and Type K even shorter, especially if it is "un-sheathed"
Steve
Bath
UK
________________________________
From: Dennis Gerasimov
To: Clayart@LSV.CERAMICS.ORG
Sent: Sat, October 10, 2009 1:39:19 PM
Subject: How to calibrate a pyrometer?
Hello fellow Clayarters,
It turns out that the pyrometer that I have is way off (judging from the
cones and other known temperature references), and in need of being
recalibrated. I tried googling up the procedure but came up mostly with
uber expensive optical pyrometer calibration apparatus. Anyone knows how
to calibrate the pyrometer, preferably without sending it off and paying
lots of $$ for the service?
All I need is a good temperature reference. For low temp digital
thermometers I always used thawing ice slurry and boiling water - these
are very reliably at 0 and 100 C. Anyone knows such reference in the
range appropriate for the K type thermocouple pyrometer?
If not, then perhaps, how do I find a service to do this in Baltimore or
DC area (so that I do not have to ship it around)?
Thanks!
Dennis
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