Computing D0 - Fluke 7312 User Manual

7312 TPW Maintenance Bath
User's Guide
11.7
11.8
68
Example:
Actual temperature = +0.132°C
Set point temperature = +0.008°C
error = +0.008– (+0.132) = -0.124 (including sign)

Computing D0

Before computing the new values for D0, the current value must be known. The
value 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 this value in case it may need to be restored in the future. The
new value D0' is computed by subtracting the temperature error from the old
value for D0 as follows.
D0' = D0 – error
Example:
Old D0 = -25.438
error = -0.124°C
D0' = –25.438 – (–0.224) = –25.662
Enter the new D0 value into the controller and press the "SET" button. Wait for
the temperature to stabilize and measure the temperature again. If desired, the
calibration procedure may be repeated to further improve the accuracy.
Calibrating the Triple Point of Water Cutout
The under temperature cutout is provided to protect the triple point of water
cell in case there is a temperature controller or sensor failure that would cause
the bath to cool rapidly below the set-point temperature. Such a failure could
cause the cell to rupture due to rapid expansion of the ice inside it. The cutout
deactivates the refrigeration thereby preventing the problem.
CAUTION: Only trained personnel should operate calibration equipment.
The cutout is calibrated at the triple point temperature at the factory. It may
need to be recalibrated from time to time if there is drift in the cutout tempera-
ture or if the cutout probe has been replaced. The actual cutout temperature
may be observed by setting the bath to a temperature well below the cutout
set-point and monitoring the bath temperature until the cutout activates. When
the display flashes tP-c-out, note the temperature. If the error is less than
0.5°C, it may be compensated for by resetting the water triple point cutout. For
greater errors it may be best to recalibrate the cutout.