John Baymore on fri 13 jul 01
So a hypothetical question....
If cone 10 is down, is the actual temperature
2381 degrees F....or a lower temp. and what temp
would the optical pyrometer measure?????<
Karen,
Optical pyrometers exist. An optical pyrometer typically works by matchi=
ng
the color of a known temperature heat source (typically an electrically
heated filament) with the hot object viewed in the background. If they a=
re
the same color...they are the same temperature. Simple in concept. The=
se
devices are typically pretty accurate..... normally an industrial or
scientific device. Might be overkill for most handcraft pottery
applications.
It is only 2381 degrees F (plus or minus the accuracy of the cone
itself.... plus or minus the error induced by how the cone was
mounted....the exact angle, plus or minus the effects of things like soda=
or wood ash, etc.) at one specific rate of climb (X degrees per hour). =
That's the heat work concept. The faster you fire the higher the end poi=
nt
temperature when you "hit cone"......... the slower....the lower. It i=
s
probably best to just never think of exact TEMPERATURE when thinking abo=
ut
cones.......... think that a cone measures in...... cones . There is=
certainly a relationship to temperature... but it is dependent on the rat=
e
of climb factor........ which is a variable that we often don't have an
exact handle on throughout a firing. But a cone is correct in relation =
to
the unit of measure called "cones". When cone 9 is down....... it is con=
e
9 .
The optical pyrometer would measure (within it's own limits of accuracy)
the temperature of the SURFACE that you happen to have it pointed at when=
you measure. There might, and likely will be, a difference in the readin=
g
depending on what you "look" at.... say.... a pot vs. the kiln wall, etc.=
. =
Like any piece of instrumentation.... any pyrometer only measures the
condition where the sensor is located (in this case...where the viewer i=
s
pointed).... not anywhere else. If the location you sample is
"representative"..... then you have a reasonable average for the chamber.=
=
If the location is NOT representative.... then all you know is what is
ahppening at the sampling location.
For a source of these try Omega Engineering. OP's are quite expensive wh=
en
compared to the other more typical pyrometers that craft potters use. Fo=
r
most craft pottery applications they are not really the "tool of choice".=
=
Cones reflect the changes in the ceramic chemistry of clay and glaze
materials....and therefore are very useful for what we typically want to
know. Pyrometers measure temperature.... and by compiling with time
readings.... are most useful in monitoring rate of climb or cooling. Tw=
o
different tools...... supply two different (but sometimes overlapping and=
related) pieces of information to the potter. Both are useful in learnin=
g.
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop August 17-26,
2001"
Karen Sullivan on mon 28 jun 04
Jeanette...
In the search for toys there is a device called
an optical pyrometer...
you point the device into a kiln and it takes
a reading from the color of the heat...
such fun...
karen
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