11
j)
If you are using a level probe, first remove the screw in the side of the probe. Insert
the probe through the stepped tube on the dewar top fitting. (Remove the pressure
relief valve if one has been fitted.) Push down firmly until the level probe is as far
down as it will go, and does not wobble. If desired, clamp the probe in position using
the screw in the side.
k)
If you are not using a level probe, make sure the pressure relief valve is pushed firmly
in place on the dewar top fitting. (First remove the screw in the side of the valve. Fit
the valve, and, if desired, clamp it in position using the screw in the side.)
l)
Push the vent valve (
) firmly into position on the vent tube until it stops. This is
a tight fit, as the vent valve is sealed by an o-ring onto the vent tube.
m)
Fill the storage dewar. (If you do not fill the dewar to the top, make sure there is at
least 10 cm of liquid nitrogen in it.) When the dewar is full, liquid nitrogen will spurt
from the vent valve - stay well away. Replace the cap.
n)
Before plugging in the controller, ensure that the voltage selector on the rear panel is
correctly set for the intended supply voltage.
o)
Connect the three cables. Just match the labels on the D-plugs with the labels on the
back of the controller. The round connectors on the sample flow unit and shield unit
are colour coded - match the colours when connecting. These connectors also have red
dots - line up the red dot on the plug with the red dot on the socket.
p)
Use the plastic tie-wraps to tidy up the system by attaching the tubes and cables
together.
nitrogen gas in
Shield flow
4-pin connector:
nozzle sensor
10-pin connector:
heater for heat
exchanger
Figure 5 Schematic of coldhead top flange
