Fluke 7381 - Cooling Control; Refrigeration

7381
User’s Guide
24
If the cutout is activated because of excessive bath temperature, power to the heater shuts off,
the bath cools, and the display flashes
Cut-out. The display flashes between the actual
temperature and
Cut-out until the temperature falls below the reset temperature and the cutout
is reset.
Cooling Control
The Bath has a fully-automated refrigeration control system when the cooling power switch on
the front panel is activated (I). Under normal conditions, the refrigeration is on at any temperature
below approximately 60 °C, see Refrigeration. When the Bath controls at temperatures between
–61 °C and 60 °C, the refrigeration is in the Hot Gas Bypass or Reduced Cooling mode.
< –61 °C, the refrigeration is in the High Cooling mode and the Hot Gas Bypass automatically
turns off. When the Bath cools from one temperature to another <60 °C, cooling is at maximum
until the temperature is within 0.5 °C of the set-point. These conditions are the default conditions
but can be altered in these ways:
• The cooling (refrigeration) can be set to operate in the auto, on, or off modes. See Cooling
Mode.
• The Hot Gas Bypass or reduced-cooling mode can also be set to on (manual), off, or auto.
These controls are available from the front panel as described Operating Parameters, or through
the digital interface as described in Interface Commands and Cooling Control. Set the cooling
mode control to automatic, on, or off. With these selections, the refrigeration is in automatic as
described above, always on, or always off. The hot gas bypass modes are similarly selectable
between automatic, on, or off. This system is in automatic as described above, always on (low-
cooling capacity, adjustable) or always off (high-cooling capacity).
The auto modes allows the Bath to operate automatically in the manner described above. The
cooling on function eliminates this auto feature and the refrigeration is on at all times unless the
front-panel switch is turned off (O) or until you make another menu selection. The Hot Gas
Bypass mode selection works the same way. The auto function is the default and active until off
or on is selected. On means it is always on with manual selection, and off is always off (or cooling
always on maximum). For different reasons, you might want to eliminate the automatic
functioning. If that is the case, make the appropriate selections with the front panel or the digital
communications interface.
Refrigeration
A compact cascade-refrigeration system that uses the ozone-safe R-507 and R-508bHFC
refrigerants provides cooling. Depending on the fluid used, and if you use the access cover,
refrigeration is often unnecessary when the Bath is >45 °C to 60 °C. The automated system
automatically turns the system off when >60 °C. The refrigeration system automatically changes
modes depending on Bath temperature and operation needs as described below. The
refrigeration system activates once the switch on the front panel is on.