Oxford Instruments Cryojet Service manual

Operator’s Handbook
Cryojet
Issue 4
January 2001
File reference: CJ250101.DOC
Part number UMC0001
Oxford Instruments
Superconductivity
Tubney Woods, Abingdon,
Oxon, OX13 5QX, England
Tel: [phone]
Fax: [phone]
E-mail:[email protected]
www.oxford-instruments.com

Contents
1 Quick User Guide ...................................................................................................... 4
2 Description of the system......................................................................................... 7
2.1 Sample flow unit ........................................................................................ 8
2.2 Shield unit................................................................................................... 8
2.3 Stand ........................................................................................................... 8
2.4 Storage Dewar ............................................................................................ 8
2.5 Controller.................................................................................................... 8
3 Unpacking and preparation..................................................................................... 9
3.1 Unpacking the system ................................................................................ 9
3.2 Preparing the system for operation .......................................................... 9
4 Controller ................................................................................................................ 13
4.1 Control of flow rates ................................................................................ 13
4.2 Control of jet temperature ...................................................................... 13
4.3 Default Conditions on Start-up ............................................................... 14
4.4 Low Nitrogen Level Cut-out..................................................................... 14
5 Operation ................................................................................................................ 15
5.1 Suggested operating conditions.............................................................. 15
5.2 Alignment of Nozzle and Use of Alignment Tip .................................... 15
5.3 Filling the dewar....................................................................................... 16
5.4 Using the dipstick to measure the level of liquid nitrogen ................... 16
5.5 Warming up the system ........................................................................... 17
5.6 Evacuating the Outer Vacuum Chamber (OVC)...................................... 18
5.7 Calibration of Sample Temperature........................................................ 19
5.8 Stability ..................................................................................................... 19
5.9 Icing of Crystal Support and Goniometer ............................................... 19
6 Control from a computer ....................................................................................... 20
6.1 RS232 Connection Hardware ................................................................... 20
6.2 GPIB (IEEE-488) Connection Hardware.................................................... 20
6.3 Control Using the Oxford Instruments ObjectBench software
package..................................................................................................... 21
6.3.1 Installation of Cryojet driver in ObjectBench........................ 21
6.3.2 Setting up the Cryojet driver ................................................. 22
6.3.3 Control of the Cryojet ............................................................ 22
6.4 Restoring Standard Calibration Parameters............................................ 23
7 Setting of P, I and D Control Terms ....................................................................... 24
8 Liquid Nitrogen Autofill System............................................................................. 26
8.1 Setting Up the Autofill System ................................................................ 27
8.2 The Solenoid Valve................................................................................... 28
9 Fault finding............................................................................................................ 29
10 Wiring Information................................................................................................. 32
10.1 Shield Unit ................................................................................................ 32

10.2 Sample flow unit: 15 way D-connector (labelled “Cryojet dewar
leg”) .......................................................................................................... 33
10.3 Sample flow unit 9-way D-connector (labelled “Coldhead”) ................ 33
Warnings
Before you attempt to install or operate this equipment for the first time, please make
sure that you are aware of the precautions that you must take to ensure your own safety.
The booklet “Safety Matters”, supplied with this manual gives advice.
Oxford Instruments Superconductivity Limited, January, 2001. All rights strictly reserved.

4
1Quick User Guide
A) If the system has not been installed and set up, see section 3.
B) Check there is at least 10 cm of liquid nitrogen in the dewar. Never allow the dewar
to become empty when the Cryojet is running.
C) Switch on the controller. See “Default conditions on startup” below.
D) Set the temperature.
E) Set the flow rates.
Suggested sample flow rate for 100 K: 6 l/min
Suggested sample flow rate for 90 K: 10 l/min
Suggested shield flow rate: 5 l/min.
For a fast cool-down, set the sample flow rate to 10 l/min initially, and then reduce it
to the desired value when the temperature is close to the set temperature.
F) Turn the automatic temperature control ON. The Cryojet will now cool to the set
temperature. (To select Automatic mode, the sample flow must be at least 2l/min. If a
flow has been selected but after a couple of minutes no flow can be felt, switch the
temperature control off and see section 9.)
G) Align the nozzle with the anticipated sample position: see “Alignment of Nozzle”
below.
100.06.04.0
Figure 1 Main features of Cryojet controller
Use only when
computer is
attached. See 6.3.3.
To set sample flow,
press and hold SET,
while pressing RAISE or
LOWER.
To set shield flow, press
and hold SET, while
pressing RAISE or
LOWER.
These turn the
automatic
temperature
control on and off
To change the set
temperature, press and
hold SET, while pressing
RAISE or LOWER.
Only use P, I and D to
change temperature control
parameters. See section 7.
Press and hold CAL/STORE and
press SET to save parameters.
(This will interrupt the flow
momentarily.)
Only use MAN if
manual control of
heater is required
HEATER light is on
when automatic
temperature
control is on.

5
Keep the plastic cap and the pressure relief valve in place on the dewar top fitting, to
prevent the ports becoming blocked by ice.
Alignment of Nozzle
The nozzle should be placed as close to the sample as possible to prevent icing - 5 mm is
recommended.
The jet should be centred on the sample. One way to do this is to use the Oxford
Instruments alignment tip. Slide the device into the nozzle, and tighten the knob to
clamp it in place. Place a sample mount with no sample on the goniometer. Adjust the
nozzle so that the sharp tip is almost touching the place where the sample would be.
Remove the sample mount. Loosen the knob and remove the alignment tip. Then place
the sample on the goniometer. If required, move the coldhead forward using the
micrometer.
Using the dipstick to measure the level of liquid nitrogen
Slowly lower the dipstick into the dewar through the fill port until it hits the bottom, and
wait a couple of seconds. Then pull it out, and wait a few seconds for frost to form on the
surface. The length of the frosted section is the depth of liquid in the dewar. Do not
touch the cold part of the dipstick with your bare hands.
Warming up the system
The system should be switched off whenever it is not in use. To prevent the remote
possibility of ice or water building up in the coldhead (which is designed to prevent this
happening), either
(a) block the inner nozzle with a rubber stopper. The cold head can then be left to warm
up naturally. Or
(b) set the temperature to 300 K and allow the displayed temperature to reach room
temperature before switching off. To speed this up, reduce the sample flow to about 3
l/min.

6
Default conditions on start-up
100.04.0
6.0
Figure 2 Procedure for putting controller into "Auto-start" mode
Start-up Condition How to set this condition up
Non-Auto Start
When Cryojet is switched on the
gas flows are zero and automatic
temperature control is OFF.
Set the temperature control off by pressing the
OFF button on the left-hand side of the front
panel.
Use the STORE function: press and hold the
recessed button CAL/STORE using a pointed object
and press the SET button in the left-hand group of
buttons. The letters “Stor” will appear on the
display. (This will interrupt the flow momentarily).
Now return the controller to Automatic
temperature control mode for normal operation.
Auto-Start
Sample flow and shield flow start
as soon as Cryojet is turned on,
with automatic temperature
control.
When the controller is switched on
it will display the message “Auto”
if it is in Auto-Start mode.
See Figure 2.
Auto-Start is useful if there is a possibility of brief
power failures when the Cryojet is running
unattended. Do not select Auto-Start
unless you are sure that there will be
liquid nitrogen in the dewar when the
controller is switched on.
2. Set the desired flow rates
3. Press
ON.
4. Press and hold CAL/STORE and press SET.
1. Set the desired
tem
p
erature

7
2Description of the system
The Cryojet is designed principally for X-ray diffraction studies. It allows a sample to be
cooled or heated using a stream of gas without the need for windows between the X-ray
source, sample and detector. Figure 3 illustrates the system.
Figure 3 Sketch of Cryojet system
Figure 4 Vent valve
Nozzle
Coldhead
Dewar
Dewar
top
Polythene tube carrying
shield flow
Vent
valve
Sample flow unit
Shield unit
Fill port
Port for pressure
relief valve or
level
p
robe.
Dewar leg (sample
flow unit)

8
2.1 Sample flow unit
The dewar leg of the sample flow unit is immersed in the liquid nitrogen in the storage
dewar. A heater at the bottom of the dewar leg boils nitrogen. The cold gas passes up
the flexible stainless steel vacuum-insulated transfer tube into the coldhead. The
coldhead contains a heat exchanger and heater. The gas then passes through the nozzle
onto the crystal, forming the sample flow. The temperature of the sample flow can be
regulated to any value between about 90 K and 300 K by the heat exchanger, using a
temperature sensor in the nozzle.
A vacuum valve is situated at the top of the rigid section of the transfer tube, from which
the Cryojet can be pumped to maintain the required thermal insulation.
2.2 Shield unit
The shield unit consists of a rigid vacuum-insulated tube that is inserted into the dewar. A
heater at the bottom boils nitrogen. At the top of the unit there is a heat exchanger, with
a heater and temperature sensor, which heats the nitrogen to room temperature. The
nitrogen flows through the central stub of the shield unit to the coldhead via a length of
polythene tubing. This shield flow then flows through the outer nozzle, preventing
atmospheric water vapour from icing up the sample or the nozzle.
2.3 Stand
The Cryojet is supported via a stand that is adjustable to suit the geometry of the user’s
experiment.
2.4 Storage Dewar
A 75 l storage dewar is used to store the liquid nitrogen used for the sample flow and
shield flow. The dewar has a top fitting with five ports as follows, shown in Figure 3.
•51 mm hole: sample flow unit dewar leg
•38 mm hole: shield unit
•Non-return vent valve
•13 mm bent tube: for filling the dewar with liquid nitrogen
•stepped straight tube: for fitting level probe or pressure relief valve
2.5 Controller
The controller controls the gas flows and the temperature of the jet.

9
3Unpacking and preparation
3.1 Unpacking the system
Carefully remove the Cryojet and all the accessories from the packing cases, and check the
packing list to make sure that you have found all of the components. Examine the system
to make sure that it has not been damaged since it left the factory. If you find any signs
of damage please contact Oxford Instruments immediately.
A complete system consists of:
•Sample flow unit
•Stand with xyz adjustable stage
•Shield unit
•Dewar top fitting and 3 bolts
•Includes fill port adaptor with flow restrictor
•For customers in the USA, 1/2” flare fitting
•Controller
•Polythene tubing (1.5 m)
•Electrical cables with the following labels:
•coldhead
•shield unit
•dewar leg (and N2 level cut-off)
•Spares kit, including:
•Allen keys (hexagonal wrenches): 8 mm, 6 mm
•Tie-wraps
•Dipstick
•Liquid nitrogen storage dewar
•Pressure relief valve
The following components are options that will only have been supplied if ordered
separately.
•Optional autofill system, or
•Liquid nitrogen hose
•Liquid nitrogen level meter and probe
•Pressurised liquid nitrogen supply dewar
•Dewar base with wheels
•High vacuum pumping system and lines
3.2 Preparing the system for operation
a) Check that the dewar top fitting is already fitted to the storage dewar, and is secured
using the three M6 screws provided. Make sure that the three small screws that hold
the top fitting together are loose. (The sample flow leg and shield leg will not slide
into the dewar top fitting if these screws are tightened.) Remove the vent valve by
pulling firmly upwards. (See Figure 4.)
b) Position the liquid nitrogen dewar about 1 metre from the intended position of the
sample.

10
c) Set up the stand approximately in the intended experimental position. Slide the stage
assembly onto the stand and clamp in position using the lever. (See Figure 6 and
Figure 7 below.) Note that the lever can be rotated to any convenient position by
pulling it to disengage the lever from the clamping mechanism.
d) Lower the sample flow unit dewar leg through the widest hole in the dewar top fitting
to the bottom. (The wide part of the dewar leg is a tight fit through the O-rings in the
top fitting.)
e) Slide the nozzle of the coldhead through the hole in the holder in the stand and
secure using four caphead screws (supplied) at the base of the nozzle. Use the pre-
existing bend of the flexible section when you arrange the coldhead in position. The
shield tube running down the side of the coldhead must fit in the slot in the side of the
holder. If the shield tube does not line up with the slot, rotate the entire dewar until it
does.
f) Arrange the nozzle approximately in its intended operating position. After you have
tilted the coldhead to the desired position, clamp the tilt adjuster in place using black
knob. You find it convenient to use the 8 mm Allen key provided at the same time. To
move the bracket assembly up or down the post smoothly, support the weight of the
coldhead by putting your hand under the stage assembly near the coldhead.
g) Lower the shield unit into the next smaller hole, all the way to the bottom of the
dewar. It is also a tight fit in the O-rings in the top fitting. Connect the fitting on the
top to the fitting on the cold head using the polythene tube supplied. To connect, just
push the polythene tube into the fitting until it stops.
h) Tighten the three small screws on the dewar top fitting.
i) Fit a suitable hose from your pressurised supply dewar to the Cryojet dewar. Some
users use polythene tube. This becomes brittle when cold, and must be used with
caution. Other plastics may not be safe, as they may be even more brittle. The fill port
is fitted with a stainless steel coupling, equipped with a flow restrictor. This coupling
has a 3/8” BSP parallel thread, with a 60°flare female sealing surface. If necessary,
remove the top part of the coupling. Systems delivered in the USA also have an
adaptor to convert this coupling to a 1/2” flare fitting (unless the system includes a
nitrogen fill hose).
If you have an Oxford Instruments autofill system, see section 8.
If you have an Oxford Instruments nitrogen fill hose, fit it as follows. The brass
adaptor fits onto your pressurised dewar, while the stainless steel adaptor fits onto the
Cryojet dewar. Remove the brass adaptor from the hose, and screw it into the liquid
outlet of your pressurised dewar, using PTFE tape. Screw the hose onto the brass
adaptor using two spanners.
Attach the other end of the nitrogen hose to the dewar top fitting, using the stainless
steel compression fitting that is already fitted to the fill port. Slide the end of the hose
onto the fill port, and tighten the nut securely using two spanners.

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 (Figure 4) 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

12
Figure 6 Coldhead and stand
(The appearance of the knobs may be different from that illustrated.)
Figure 7 Close-up of stand assembly
tilt adjust
SEE
DETAIL
xyz fine
adjustment
Coarse
height
dj t

13
4Controller
Full details are in the Cryojet Controller Technical Handbook, included together with this
manual. See also Figure 1.
4.1 Control of flow rates
The flow rates of the sample flow and shield flow are shown on the display in l/min (as if
they were measured at atmospheric pressure and 293 K). To change the flow to any value
from 0 to 10 l/min, hold down the SET button underneath the appropriate display and
press RAISE or LOWER.
4.2 Control of jet temperature
There are three modes of operation: Automatic, Manual and Heat Exchanger Off. The
light labelled “Heater” is on if the controller is in Automatic mode, or if it is Manual mode
with non-zero voltage supplied to the heat exchanger.
Automatic
In this mode, the temperature of the jet is controlled automatically.
To put the controller into Automatic mode, press the ON button on the left-hand side of
the front panel.
To display the Set Temperature press SET (left hand block of buttons) and keep it pressed.
To change the Set Temperature, hold down SET while using RAISE and LOWER.
To display the voltage being supplied to the heat exchanger at a given moment, press and
hold the ON button on the left-hand side of the front panel.
To select Automatic mode, the sample flow must be at least 2l/min. If a flow has been
selected but after a couple of minutes no flow can be felt, switch the heat exchanger off
and see section 9.
Manual
In this mode, a fixed voltage is supplied to the heater in the heat exchanger. It is not
recommended for routine operation.
To select Manual mode, press MAN. The default voltage is zero.
To display the voltage supplied to the heat exchanger, press and hold MAN.
To change the voltage supplied, press and hold MAN, and use RAISE and LOWER.
Heat Exchanger Off.
In this mode, no voltage is supplied to the heater in the heat exchanger. This mode will
give the lowest possible temperature, but there will be some temperature variation.
To set this mode, press the OFF button on the left-hand side of the front panel.

14
4.3 Default Conditions on Start-up
There are two choices of start-up conditions, referred to as “Auto-Start” and “Non-Auto
Start” as follows.
Non-Auto Start
•Gas flows equal zero;
Heat exchanger is Off
To set these start-up conditions:
Set the heat exchanger off by pressing the OFF button on the left-hand side of the front
panel.
Use the STORE function: press and hold the recessed button CAL/STORE using a pointed
object and press the SET button in the left-hand group of buttons. The letters “Stor” will
appear on the display. (NB This will interrupt the flow momentarily.)
Auto-Start
•Gas flows non-zero - can be configured to any desired value.
Heat exchanger in Automatic mode
Auto-Start is useful if there is a possibility of brief power failures when the Cryojet is
running unattended. Do not select Auto-Start unless you are sure that there
will be liquid nitrogen in the dewar when the controller is switched on.
To set these start-up conditions use this procedure, illustrated in Figure 2:
1. Set the desired SET temperature.
2. Set the desired start-up gas flows.
3. Set Automatic mode by pressing the ON button on the left-hand side of the display.
4. Use the STORE function: press and hold the recessed button CAL/STORE using a
pointed object and press the SET button in the left-hand group of buttons. The letters
“Stor” will appear on the display. (This will interrupt the flow momentarily).
When the controller is switched on it will display the message “Auto” for a second or two
if it is in Auto-Start mode.
4.4 Low Nitrogen Level Cut-out
A sensor attached to the sample flow unit dewar leg detects the presence or absence of
liquid nitrogen. If the liquid level is below about 6 cm from the bottom of the dewar, all
the heaters in the system will switch off automatically and the message “Lo N” will be
displayed. To restore normal operation after you have refilled the dewar, you must switch
the controller off and on again.

15
5Operation
5.1 Suggested operating conditions
Always keep at least 10 cm of liquid in the dewar when the Cryojet is running, as lower
levels could impair the performance. Never allow the dewar to become empty when
the Cryojet is running.
Keep the plastic cap, the vent valve and the pressure relief valve (or level probe) in place
on the dewar top fitting, to prevent water from the atmosphere entering.
A sample flow rate of about 6 l/min is recommended for most applications. (See 4.1 for
how to set these flow rates.) The lower the flow rate, the higher the base temperature
will be. Lower flow rates may be suitable if very low temperatures are not required,
provided the sample can be placed very close to the nozzle. A flow rate of 4 - 5 l/min is
usually sufficient for the shield flow - lower flow rates can be used if they are sufficient to
stop the sample and nozzle icing up.
For a fast cool-down, set the sample flow rate to 10 l/min initially, and then reduce it to
the desired value when the temperature is close to the set temperature.
5.2 Alignment of Nozzle and Use of Alignment
Tip
The nozzle should be placed as close to the sample as possible to prevent icing. The
limitation on this spacing depends on the diffraction angle required and the angle
between the nozzle and the incoming x-ray beam. In almost every case the nozzle should
be within 10 mm of the sample.
The jet should be centred on the sample as accurately as possible. One way to do this is to
adjust the nozzle first so that the sample is in the plane of the nozzle. This makes it easier
to centre the nozzle. Then move the nozzle back to the desired position using the
micrometer stage. See Figure 8.
Another method is to use the Oxford Instruments alignment tip. Slide the device into the
nozzle, and tighten the knob to clamp it in place. Place a sample mount with no sample
on the goniometer. Adjust the nozzle so that the sharp tip is almost touching the place
where the sample would be. Remove the sample mount. Loosen the knob and remove
the alignment tip. Then place the sample on the goniometer. If required, move the
coldhead forward using the micrometer.

16
Figure 8 Possible alignment technique
5.3 Filling the dewar
The Cryojet can be run continuously for as long as required. The dewar can be refilled
while the Cryojet is running.
Fit the liquid nitrogen hose from your supply dewar onto or into the fill tube. Make sure
it is held in place so that it will not be blown free by the pressure of nitrogen during the
fill. Use a low pressure in the supply dewar - preferably less than 1 bar. Open the valve on
the supply dewar slowly, as the sample flow temperature may be temporarily affected by
an increase in pressure in the dewar. Close the valve on the supply dewar slowly to stop
the fill.
5.4 Using the dipstick to measure the level of
liquid nitrogen
A dipstick (a long plastic rod) has been provided as a simple way of estimating the level of
liquid in the dewar. (A digital level meter and probe are also available - see separate
manual if these have been supplied.) Slowly lower the dipstick into the dewar through
the fill port until it hits the bottom, and wait a couple of seconds. Then pull it out, and
wait a few seconds for frost to form on the surface. The length of the frosted section is
the depth of liquid in the dewar. Do not touch the cold part of the dipstick with your
bare hands.
For depths between 10 cm and 80 cm, the dewar holds about 0.98 litres for every
additional centimetre of liquid. (See calibration chart below.) A flow of 1 litre/min of gas
corresponds to a consumption of 0.086 litre/hour of liquid, i.e. about 0.088 cm/hour. In
addition, there is a boiloff from the dewar of about 0.10 cm/hour
Centre nozzle in
this position
Withdraw nozzle to
this position for
diffraction studies
Sample

17
Cryojet dewar calibration
0
10
20
30
40
50
60
70
80
0 102030405060708090
Depth of liquid, cm
Volume, litres
Figure 9 Cryojet dewar calibration
5.5 Warming up the system
The system should be switched off whenever it is not in use. To prevent the remote
possibility of ice or water building up in the coldhead (which is designed to prevent this
happening), either
a) Block the inner nozzle with a rubber stopper. The cold head can then be left to warm
up naturally.
Or
b) Set the temperature to 300 K and allow the displayed temperature to reach room
temperature before switching off. To speed this up, reduce the sample flow to about 3
l/min.
If you do not use the Cryojet for several days, the dewar can warm up. It is then possible
for water to collect at the bottom. This could block the system when it freezes, although
the dewar legs have been designed to prevent this. This can be prevented in several ways:
(a) Before allowing the dewar to warm up, raise both dewar legs. To do this, loosen the
three small screws in the dewar top fitting. Raise the shield unit and the sample flow
unit dewar leg by a centimetre or two, then clamp them in place by tightening the
three small screws. Leave them in place when you later refill the dewar. (To maximise
the available time between refills, you may want to lower the legs to the bottom
later, but it is easier to do this when the dewar top fitting is no longer cold from the
filling process.); or
(b) Before refilling a warm dewar, attach a dry air or nitrogen supply to the outer nozzle.
Gas will then flow backwards through both the sample flow unit and the shield flow
unit, blowing out any water from the holes at the bottom.

18
If either the sample flow dewar leg or the shield unit is removed from the dewar, then
before putting it back check that the small holes in the bottom are clear of ice, using a
stiff wire such as a paper-clip.
It is not possible to remove the shield unit from the dewar top fitting when it is cold. To
dismantle the system when cold, remove the entire system including the dewar top fitting
from the dewar in one unit.
5.6 Evacuating the Outer Vacuum Chamber
(OVC)
The OVC of both the sample flow unit and shield unit have to be pumped to high vacuum
to make sure that they provide the required thermal insulation.
Both are pumped in the factory, but this needs to be repeated occasionally. When the
system is new, all of the materials inside the vacuum space are likely to outgas quickly, and
this will affect the quality of the vacuum. This does not mean that the system is leaking.
The OVC of the sample flow unit should be pumped if either of the following symptoms
appear:
•The sample flow unit feels cold to the touch, or condensation or frost appears. Some
condensation or frost is normal on and just above the dewar top fitting.
•The jet does not reach the desired temperature, or the voltage supplied to the heat
exchanger heater is lower than that given for the relevant temperature in the test
results appended to this manual.
If the Cryojet has not been used for a month or more and the dewar has warmed up, it is
often advisable to pump the vacuum in the sample flow unit before starting to use it
again.
The OVC of the shield unit should be pumped out whenever water or ice condenses on the
outside of the rigid dewar leg. Some condensation is normal on and just above the dewar
top fitting.
Both OVCs contain a sorb at the bottom of the dewar leg. Ideally they should be pumped
overnight, and during pumping the dewar leg should be heated to about 100 ºC to make
sure that the sorb outgasses. You can do this by setting the appropriate flow rate to 8
l/min (not more) with the dewar leg out of the dewar. You must support the dewar leg so
that the bottom end is not touching anything that could melt. Do not insulate it in any
way, as this could cause overheating. Before you set the flow rate you must over-ride the
low nitrogen level cutoff by removing the plug from the socket labelled “Low nitrogen
level cutoff” on the back of the controller. Remember to replace the plug afterwards.
Do not bake the flexible transfer tube or coldhead as these contain plastic components.
It is also possible to pump the OVC while the Cryojet is operating, although the vacuum
will not last as long in this case, as the sorb has not been outgassed.

19
Pumping with a two-stage rotary pump that has a base pressure of about 10-3 mbar is
sufficient. A diffusion pump or turbo pump would also be suitable.
5.7 Calibration of Sample Temperature
Precise estimation of the temperature of a real sample in the cold jet is not
straightforward, as it will be affected by the size and location of the sample, the
orientation of the nozzle, and by heat conduction along the sample support. Contact
Oxford Instruments for calibration information.
5.8 Stability
The temperature displayed is normally stable to about 0.1 K. Small fluctuations in
temperature will occur when the dewar is refilled.
5.9 Icing of Crystal Support and Goniometer
The shield flow is designed to prevent icing of the sample and nozzle. A slight build-up of
snow is likely on the crystal support and goniometer. In most cases no action need be
taken, provided that the incoming beam can be collimated to exclude any ice on the
crystal support. Increasing the shield flow rate to 10 l/min for a minute or so may help to
remove frost from the crystal support.

20
6Control from a computer
The controller can also be controlled from a computer using the RS232 interface or the
optional GPIB (IEEE-488) interface. In either case, you can use the ObjectBench software
provided. An installation manual is provided. Windows 95 or 98 is required. This section
explains the basics of how to control the Cryojet. Full information on topics such as
plotting parameters against time, saving data to a file, and creating macro programs is
available through the on-line help.
A unique feature of the Cryojet controller and other Oxford Instruments products is the
ability to connect a number of instruments simultaneously, to a single RS232 port on a
computer, and to control each one independently. This is done by means of an Isobus
cable which carries a single “master” connector (25-way D socket) and up to eight, daisy-
chained “slave” connectors (25-way D plugs). This is available from Oxford Instruments
Cryospares.
6.1 RS232 Connection Hardware
The bi-directional serial data link from the computer is connected via a 25 way D-socket on
the rear panel. The controller is configured as a DCE with the standard pin outs given
below. The majority of computer RS232 interfaces are configured as a DTE and are fitted
with a 25 way D plug. For this type of connector, a simple lead connecting pin 1 to pin 1,
pin 2 to pin 2 and so on is all that is required. For computers fitted with a 9 way D plug for
RS232, (AT style COM port), a standard "AT lead" fitted with a 9 way socket and a 25 way
plug is required.
If for any reason you plug the computer into a different electricity supply circuit from the
Cryojet controller, you should use an Oxford Instruments ISOBUS cable to ensure electrical
isolation.
6.2 GPIB (IEEE-488) Connection Hardware
If the optional GPIB interface is fitted, connections to the GPIB are made via a standard 24
way GPIB cable, conforming to the standard IEEE-488.1. Connections should be made
using a standard GPIB cable. If you wish to connect both a Cryojet controller and a level
meter to a GPIB port on a computer, use a “GPIB Gateway” - contact your sales engineer
or Oxford Instruments Cryospares.
Note: GPIB connections should never be made or broken whilst the controller or any of
the instruments connected to the Bus are powered up. Failure to observe this
precaution can result in damage to one or more instruments.
Never plug the computer into a different electricity supply circuit from the Cryojet
controller.