| Acoustic
and Ultrasonic
The
concept of measuring temperature in a gas by measuring the speed of sound in that
gas has been exploited by several groups.
Another variation on the same idea has been to send ultrasonic pulse down a rod
of known expansion and propagation properties. By placing slots in the rod at
known and calculable distances from the excitation position, one could immerse
the rod in a medium of high temperature and then measure that temperature by measuring
the reflection times of the pulses from the notches. A
vendor of these devices is:
SEI in Nevada-USA
An innovator in acoustic pyrometers for measuring the
temperature of hot gases in the combustion chambers of boilers.
Noise
Johnson noise
thermometers have been around for 30 years or more. They are very complex and
were difficult to fabricate with the electronics of 30, 20 even 10 years ago.
That's changing rapidly as better and better IC circuits become available and
the processing capability of micro-computers continue to grow. The best way to
appreciate what can and has been done with these devices is to check the links. Much
R&D has been done on Noise Thermometry by the Instrumentation Group at The
USA Department of Energy's Oak Ridge National Laboratories Suction
Pyrometer
You've never heard of it, right? Many people are in the same
fix as you. The name sounds familiar but not exactly a household word. Yet these
radiation-shielded thermocouple devices make a real difference in the measurement
of high temperature gases. They are even made commercially by a few companies
on a regular basis A
vendor of Suction Pyrometers is:
Land Combustion Division of Land Instruments, International Venturi
Pneumatic Pyrometer
That doen't ring a bell either. But they exist and
sometimes are the only device to measure gas temperatures at temperatures above
the range of thermocouples. Big, bulky and cumbersome, they are nonetheless the
only way to go when nothing else works. A
vendor of Suction Pyrometers used to be:
Land Combustion Division of Land Instruments, International
Optical
There
must be a dozen, if not more, variations on techniques to measure the temperature
of an optically active sensing element that has some property that varies in a
known fashion with temperature. Polarization, transmission, expansion, band-gap
edge shift are but a few such properties.
Needless
to say, we've left room for expansion on this page, because it will be
needed!
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