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User's Guide
52
Computing R
0
and ALPHA
Before computing the new values for
R
0
and
ALPHA
the current values must be
known. The values may be found by either accessing the probe calibration menu
from the controller panel or by inquiring through the digital interface. The user
should keep a record of these values in case they may need to be restored in the
future. The new values
R
0
and
ALPHA
are computed by entering the old values
for
R
0
and
ALPHA
, the calibration temperature set-points
t
L
and
t
H
, and the
temperature errors
err
L
and
err
H
into the following equations:
If for example
R
0
and
ALPHA
were previously set for 100.000 and 0.0038500
respectively and the data for
t
L
,
t
H
,
err
L
, and
err
H
were as given above then the
new values
R
0
and
ALPHA
would be computed as 99.885 and 0.0038302
respectively. Program the new values
R
0
and
ALPHA
into the controller. Check
the calibration by setting the temperature to
t
L
and
t
H
and measuring the errors
again. If desired the calibration procedure may be repeated again to further
improve the accuracy.
Calibration Example
The bath is to be used between 25 and 75
°
C and it is desired to calibrate the
bath as accurately as possible for operation within this range. The current values
for
R
0
and
ALPHA
are 100.000 and 0.0038500 respectively. The calibration
points are chosen to be 30.00 and 80.00
°
C. The measured bath temperatures
are 29.843 and 79.914
°
C respectively. Refer to Figure 10 for applying equations
to the example data and computing the new probe constants.
