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If the Bath is below the 60 °C cutoff point and is set to a temperature >60 °C, refrigeration shuts
off to protect the Bath from overheating and creating excessive internal pressures. If the Bath is
>60 °C and is set to a new temperature below the cutoff temperature, refrigeration turns on again
at 59 °C.
As the Bath controls at temperatures between 60 °C and –61 °C, the Bath operates in a low-
cooling capacity mode with the Hot Gas Bypass valve on (HGb on). See
When the Bath is cooled and the new set-point is at least 2 °C below the current bath
temperature, the cooling turns to maximum capacity (HGb off) until the Bath is within about
0.5 °C of the new set-point. This provides the fastest cooling possible to achieve the new set-
point temperature.
When you heat the Bath and the new set-point is at least 5 °C above the current bath
temperature, the refrigeration turns off until the bath is about 1.5 °C below the new set-point. This
permits the maximum heating rate to reach the higher temperatures as quickly as possible.
(When the scan rate is active this function is modified, see Scan. The cooling remains off at
temperatures >60 °C.
The automatic cooling mode might not be ideal for all circumstances. The automatic mode can be
turned off to permit manual control.
These situations benefit from cooling mode changes:
•
When you select the scan mode and the desired cooling scan requires maximum cooling
capacity in a range where the hot gas bypass would normally be on.
•
The application requires maximum cooling capacity when the hot gas bypass would normally
be on.
•
When you use the bath at temperatures <–61 °C in an ambient temperature <23 °C, a small
stability benefit might be realized if you use the hot gas bypass.
•
The refrigeration can be beneficially used for short times (<1 hr) >60 °C but <100 °C.
This list is not complete, but suggests some situations when automatic modes might not be best.
Fluke Calibration recommends use of the automatic functions as they are adequate.
Calibration Bath
Refrigeration
Hot Gas Bypass
Mode.
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