TA Instruments TMA 2940, Operator'S Manual

Page: 73 / 176

TA I
NSTRUMENTS
TMA 2940 3–7
Calibrating the TMA
Temperature Calibration
Temperature calibration is based on a run in
which a temperature standard (e.g., indium) is
heated through its melting point. The recorded
melting point of this standard is compared to the
known melting point, and the difference is
calculated for temperature calibration.
In addition, you can use up to four other stan-
dards to calibrate temperature. If you use one
pair of known and observed points, the entire
curve is offset, or shifted, to the actual melting
point. If you use multiple standards, the tem-
perature is corrected by a cubic spline fit. The
multiple-point temperature calibration is more
accurate than the one-point calibration.
For all probe types, except the film/fiber acces-
sory, small flattened pieces of standard metals
are placed on the stage. To protect the stage
from amalgamation with the metal, it is recom-
mended that aluminum or platinum be placed
between the stage and the metal standard. The
end of the probe can also be wrapped with foil
for added protection.
For the film/fiber probe, metal wires can be
crimped into the aluminum balls and used for
calibration.
When to Calibrate:
The sample thermocouple should be calibrated
in the following situations:
• When the TMA is first installed