opening. The fiber ceramic insulation provided may be added or removed
to do this. Generally the bottom position must be filled and additional
spaces above may be filled as required.
•
Check of the Controller Set-point Accuracy:
This test is carried out in
a metal freeze point cell where the metal has been completely melted.
Prepare the furnace in the same fashion as though a freeze plateau would
be conducted up to the point that the metal sample is melted. This exam-
ple illustrates measurements made near the silver point:
♦
Set the temperature of the furnace at 964°C and allow it to stabilize as
would be done in preparation for a freeze. Measure the EMF of a ther-
mocouple inserted into the cell. Compare the measured EMF to one
taken at the M.P. or F.P. The actual temperature,
t
, in the cell can be
calculated by using the following equation:
t
E
E
=
° +
−
°
961 78
0 0114
1
0
.
.
C
mV C
where E
1
is the measurement EMF and E
0
is the EMF at the M.P. (961.78°C is
the M.P. temperature of copper for this example) and 0.0114mV/°C is the sen-
sitivity of a Type S thermocouple near the M.P. of silver.
For example, the measured EMF E
1
=9.1502 mV, the EMF at the M.P.
E
0
=9.1481 mV, the actual temperature in the furnace.
t
=
+
−
=
°
961 78
91502
91481
0 0114
961 96
.
.
.
.
.
C
Since
t
=964.0°C = the actual set-point, the error, if any, is very small. If the er-
ror is larger than 1°C, you can make an adjustment to the set-point.
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