Fluke 7008 - Computing D and D; Calibration Example

7008
Users Guide
11-2
11.3 Computing D
O
and D
G
Before computing the new values for D
O
and D
G
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 re-
stored in the future. The new values D0 ' and DG ' are computed by entering the
old values for D0 and DG, the calibration temperature set-points t
L
and t
H
, and
the temperature errors err
L
and err
H
into the following equations,
0
)0()0(
0 D
tt
DterrDterr
D
LH
LHHL
+
−
−−−
=
′
DG
tt
errerr
GD
LH
LH






+
−
−
=
′
1
If for example D0 and DG were previously set for –25.229 and err
H
were as given
above then the new values D0' and DG' would be computed as −25.831 and
.0028720 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
L
and t
H
and measuring the errors
again. If desired the calibration procedure may be repeated again to further
improve the accuracy.
11.4 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 D0 and DG are −25.229 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.