Cannon Instrument TESC - Manual (Page 25)

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CANNON®
TESC Operator's Manual, Rev 1.0
Calibrating the TESC System
CANNON Instrument Company® calibrates all TESC Systems as part of the manufacturing
process. However, differing ambient conditions during usage may necessitate adjusting the
offset values applied to the Watlow® controller and Brookfield® viscometer to ensure accurate
results.
Two resistance thermometers installed in the thermal core monitor the temperature of the
unit. The temperatures measured by these thermometers must be adjusted with an offset
value to match the actual temperature of the sample being tested. For example, a temperature
at the thermal core of –40 °C may result in the sample being at –39 °C due to the ambient air
temperature of the lab warming the sample slightly.
The Watlow® controller manages the temperature of the TESC base unit via an RTD probe
located in the thermal core in front of the test chamber. The Watlow® controller displays the
adjusted temperature. In the example, the Watlow® controller displays a temperature of –
40.0 °C, but it is known that the sample is actually at –39.0 °C (see Table 11, row 1). To correct
for this deviation, slightly more than +1 °C is added to the Calibration Offset value of the
Watlow® controller, such as +1.1 °C (see Table 11, row 2). Because the Watlow® controls the
temperature of the TESC core, this adjustment results in the sample gradually cooling to –40.0
°C when the Watlow® controller is programmed to –40.0 °C (see Table 11, row 3).
Table 11 — Watlow® offset example
Watlow®
Display
Calibration Offset Thermal Core
Sample
Temperature
1 –40.0 °C = 0 + –40.0 °C –39.0 °C
2 –38.9 °C = +1.1 °C + –40.0 °C –39.0 °C
3 –40.0 °C = +1.1 °C + –41.1 °C –40.0 °C