 When a bare thermocouple is introduced into a flame for the measurement of
gas temperature, errors arise due to the radiative exchange between the thermocouple and
its surroundings. In the standard suction pyrometers a platinum-rhodium thermocouple,
protected from chemical attack by a sintered alumina sheath, is surrounded by two
concentric radiation shields. The gases are drawn between the shields and over the sheath
with high velocity (min. 150 mls) so that the equilibrium thermocouple temperature is
nearly that of the gases without the need for correction.
The gases are normally sucked in a
dynamic position through a hole drilled at the side of the outer shield with the end of
the shield closed with a cement plug.
However, when low dust
concentrations are present in the flame, the hole can be placed in the wake of the shield
to minimize blockage. Similarly, for highly solids laden jets, two holes may be drilled in
the outer shield to allow large particles to flow directly through the shield without
deposition.
Pt-PtRh 10% (ANSI Type S)
thermocouples in combination with a silimanite shield have a recommended temperature range
from 0 to 1450C. PtRh 30% (ANSI Type B) thermocouples and alumina shields are adopted for
higher temperatures with a range from 0 to 1700C. Practically, the former arrangement can
be used up to 1650 and the latter up to 1800C. Higher temperature versions are currently
under development. All these elements are easily replaceable.
The response time of the instrument
depends upon the size of the shields and the suction velocity. From ambient to 1600C and
with a suction velocity of 250 in/s the time to achieve equilibrium is of the order of 3
min., and for subsequent temperatures changes of 100C, about 1 min.
VENDOR: IFRF Research Station b.v.
Would you be interested in:
- getting more information about
this measurement equipment?
Please contact us:
IFRF Research Station B.V.
P.O. Box 10 000
1970 CA IJmuiden
The Netherlands
email: sales@ifrf.net
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