CryoTel® GT User’s Manual Version 6 P a g e | 15
a. Proper operation of the CryoTel ®GT requires a minimum loading of 6 Watts. If minimum
load requirements are not met, the stabilized temperature will be below 77 K.
Figure 13: CryoTel® GT Controller
C. Operation Shutdown
1. Turn off the controller.
a. The quick rattle heard when power is cut off from the CryoTel ®is due to the stored energy
in the vibration absorber being dissipated.
b. In rare cases where the operating temperature was below 60 K, it has been observed that
the cooler can energize itself during shutdown and become an engine. To prevent this, allow
the cold tip to reach a temperature above 60 K before shutting down.
2. Allow the cold tip and the rest of the cryocooler temperature to rise to room temperature before
opening the vacuum in order to prevent the vapor outside the cryostat from condensing and
freezing on the cold tip.
a. Applying a heat load to the cold tip during the warming process reduces the time needed to
reach room temperature.
b. Sunpower recommends using a relay in conjunction with the temperature sensor to ensure
that the power supply to the heat load shuts off when the cold tip temperature reaches 300
K.
XI. LED and Digital Output 4
The two LEDs, shown in figure 14, indicate whether the cooler has reached its set point temperature or
if the cooler is still in cool down mode. The red LED will be on as long as the cooler is not at the
temperature setpoint. When the cooler reaches its set point temperature within the desired
temperature band the green LED will turn on. The default temperature band is 0.5K. See Section XIII,
page 27 for details on changing the temperature band.
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