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Oxford Instruments Cryojet, Руководство оператора

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6

 

Control 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.

Содержание Cryojet

Страница 1: ...y 2001 File reference CJ250101 DOC Part number UMC0001 Oxford Instruments Superconductivity Tubney Woods Abingdon Oxon OX13 5QX England Tel 44 0 1865 393 200 Fax 44 0 1865 393 333 E mail superconductivity oxinst co uk www oxford instruments com ...

Страница 2: ...e 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 Install...

Страница 3: ...arnings 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 ...

Страница 4: ...c 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 0 6 0 4 0 Figure 1 Main features of Cryojet controller Use only when computer is attached See 6 3 3 To set sample flow press and hol...

Страница 5: ... 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 dips...

Страница 6: ... 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...

Страница 7: ...f 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 probe Dewar leg sample flow unit ...

Страница 8: ... 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 s...

Страница 9: ...f 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 sy...

Страница 10: ...e 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 dew...

Страница 11: ... 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...

Страница 12: ...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 ...

Страница 13: ... 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 c...

Страница 14: ...trogen 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 but...

Страница 15: ... 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 ...

Страница 16: ... 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...

Страница 17: ...ble 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 th...

Страница 18: ...xchanger 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 ...

Страница 19: ...tact 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 ...

Страница 20: ...andard 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 an...

Страница 21: ...h command is found Command to be selected or information to be entered Result Main ObjectBench Configure Configure Submenu appears Configure submenu Add remove instruments Configure Instruments window appears Configure Instruments Add Load instrument drivers window appears Load instrument drivers Select driver cryojet drv Change the configuration name or leave it as default if only one Cryojet is ...

Страница 22: ...he default value of 1 providing no other instrument on the ISOBUS at the same time uses the same address Configure Interface window appears Cryojet driver Configure interface Set address Then follow the instructions on the screen Physical Cryojet controller front panel Press and hold CAL STORE and press SET NB This will interrupt the flow momentarily The address is stored in the EEPROM so it is no...

Страница 23: ... restored to the state in which it left the factory by using the back up disc provided and ObjectBench software Use the following sequence of operations and menu selections This feature is not available from the Cryojet instrument driver Instead you must add the instrument driver called ITC503 drv using Configure Add remove instrument Add DISCONNECT the Cryojet driver if it is connected If the con...

Страница 24: ...pecified as a time or as repeats per minute RAISE and LOWER may be used to vary the control terms whilst in LOCAL control When you have changed the values carry out a STORE command as follows Press and hold the recessed button CAL STORE and press SET This will store the new values in non volatile memory NB This will interrupt the flow momentarily If a STORE command is executed when the controller ...

Страница 25: ...sponse without excessive overshoot g If overshoot remains a problem following a large step change in SET try the effect of adding some DERIVATIVE action A good initial setting is half to one third of the system response time measured above This will probably require P to be re optimised for best results h When optimising P I and D the aim should be to achieve the lowest values of all three terms c...

Страница 26: ...ut consulting an expert The autofill system consists of the following components Nitrogen level probe Level probe cable Nitrogen hose with solenoid valve Nitrogen level meter with IEC power cable The pressurised supply dewar is normally provided by the customer The level meter has its own detailed manual but this section describes the basic operation as part of an autofill system The level meter h...

Страница 27: ...the solenoid valve indicates the correct voltage Remove fitting A from nut B on the autofill assembly Figure 10 Figure 10 Autofill nitrogen hose detail of the end near the pressurised dewar Screw fitting A into the liquid outlet of your pressurised dewar using PTFE tape The appearance of item A will depend on your dewar Engage the brass tube into fitting A ensuring the ferrule is correctly positio...

Страница 28: ...compression fitting from the end of the hose The restrictor is a plastic plug with three holes glued inside this fitting You can either drill a larger hole in this plug or request a new plug with no restrictor from your Oxford Instruments sales representative Note This will increase the temperature fluctuation caused by filling The autofill is ready for use If the Cryojet dewar is below the FILL l...

Страница 29: ...Reduce the set temperature and switch the controller off and on again Alternatively the nozzle sensor is faulty or the cable is not connected Controller will not stay in Auto mode Heater light will not stay on Sample flow must be at least 2 l min RAISE LOWER and Heater On Off do not work Controller is set to REMOTE Press LOC REM to restore to LOCAL control unless controller is LOCKED in REMOTE mod...

Страница 30: ...2 If you can feel some flow with your hand at 10 l min sample flow and 0 l min shield flow and the temperature does drop a little set the heat exchanger to 300 K with the sample flow at 10 l min Purge the coldhead in this way for at least an hour For the first few minutes check continually that there is some flow through the inner nozzle as the heat exchanger could overheat otherwise If method 2 d...

Страница 31: ...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 Th...

Страница 32: ... the socket you have disconnected 10 1 Shield Unit Component Pins on 15 way D connector Pins on round connector fixed to shield leg Typical resistance between pins when disconnected from controller ohms Typical output of controller measured using the spare socket Cryojet dewar leg when shield leg is plugged in Boiloff heater 2 and 10 7 and 8 35 40 up to about 40 volts depending on flow Heat exchan...

Страница 33: ...tor labelled Coldhead Component Pins on 9 way D connector Pins on round Fischer connectors fixed to coldhead Typical resistance between pins when disconnected from controller Typical output of controller measured when D plug is removed Heat exchanger heater 6 and 7 1 and 2 of 10 pin connector 35 40 ohms usually 0 2 V Platinum sensor voltage leads 1 and 2 1 and 2 of 4 pin connector about 105 ohms a...

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