Computing Do And Dg; Calibration Example - Fluke 2100 User Manual

8.3.3

Computing DO and DG

Before computing the new values for DO and DG 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 DO ' and DG ' are computed by entering the old values
for DO and DG, the calibration temperature set-points tL and tH, and the
temperature errors err
err ( t
= '
H L
D 0

err
= '
L
D G

t

L
If for example DO and DG were previously set for −25.229 and 186.9740
respectively and the data for t
new values DO ' and DG ' would be computed as −24.880 and 185.728
respectively. Program the new values DO and DG into the controller. The new
constants will be used the next time the bath temperature is set. Check the
calibration by setting the temperature to t
If desired the calibration procedure may be repeated again to further improve the
accuracy.
8.3.4

Calibration Example

The system is to be used between 25 and 75 °C and it is desired to calibrate the
controller as accurately as possible for operation within this range. The current
values for DO and DG are −25.229 and .0028530 respectively. The calibration
points are chosen to be 25.00 and 75.00 °C. The measured bath temperatures
are 24.869 and 74.901 °C respectively. Refer to Figure 10 for applying equations
to the example data and computing the new probe constants.
and err into the following equations,
L H
− − −
D ) 0 err ( t D ) 0
L H
−
t t
L H
− 
err
+
H
1 DG

−
t

H
, t , err
L H
+
D 0
, and err were as given above then the
L H
and t and measuring the errors again.
L H
Calibration Procedure
8.3 Thermistor Probe Calibration
8
8-5