31
Cryostat will not reach its
specified base temperature
Check that there is at least 10 cm of liquid in the
storage dewar.
Move the dewar so that the curve of the flexible
transfer tube is as gentle as possible - avoid sharp
bends. It may help to tilt the coldhead closer to the
horizontal.
Pump the vacuum in the OVC.
Polythene tube carrying shield
flow develops heavy
condensation or frost.
Check that the shield flow rate responds to changes in
the flow rate set using the controller. If the actual
shield flow is high even when it is set to 0 l/min, the
controller is at fault. See also below “Suspected fault
in a heater or sensor”.
The controller fails to operate:
Check fuses as follows.
The main electricity supply plug is fused in some
countries.
The fuse for the controller is located behind the
voltage indicator on the back panel.
Ice forms on the nozzle
Check that the shield flow is sufficient, and that the
polythene tube is connected.
The shield unit could be blocked. Remove entire
system from dewar, and warm it to room
temperature. Check with a wire or paper clip that the
holes at the base of the shield unit and sample flow
unit dewar leg are clear. Dry the system, and replace
it in the dewar. To prevent recurrence, see 0.
Suspected fault in a heater or
sensor
See section 10.
