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Oxford Instruments ILM200 Operator's Handbook Manual

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Operator's Handbook
ILM200
Family of Cryogen Level Meters
Issue 1.5
April 2000
File reference: ILM-15.DOC
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

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Summary of Contents for Oxford Instruments ILM200

  • Page 1 Operator’s Handbook ILM200 Family of Cryogen Level Meters Issue 1.5 April 2000 File reference: ILM-15.DOC 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...

  • Page 2: Table Of Contents

    Contents Introduction ......................5 Use of this Manual..................5 Description of the ILM200 Family .............. 5 Principles of Operation ................5 1.3.1 Helium Level Probe..............5 1.3.2 Nitrogen Level Probe..............6 1.3.3 Why Two Different Sensing Methods Are Used ..... 6 Safety.........................
  • Page 3 Use with Oxford Instruments ISOBUS............23 The GPIB Interface ..................24 6.6.1 Sending Commands via the GPIB........... 25 6.6.2 Accepting Responses via the GPIB ......... 25 6.6.3 The Status Byte, Use of a Serial Poll ........25 6.6.4 Use of the Service Request Line ..........26 6.6.5...
  • Page 4 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.  Oxford Instruments Superconductivity Limited, April 2000. All rights strictly reserved.

  • Page 5: Introduction

    Description of the ILM200 Family ILM200 is a family of Intelligent Cryogen Level Meters with general application in systems containing liquid helium or liquid nitrogen. The family comprises five instruments. The last two digits of the type number specify the number of helium and nitrogen channels respectively.

  • Page 6: Nitrogen Level Probe

    Prior to firmware version 1.08, ILM was designed to handle the standard Oxford Instruments probe wire, with a typical resistivity of 178 ohms/metre. Since version 1.08 this parameter may be adjusted up to a maximum value of 200 ohms/metre. There are now two types of wire in use:.

  • Page 7: Safety

    2 Safety The following general safety precautions must be observed during the operation, service and repair of this instrument. Protective Ground To minimise shock hazard the instrument must be connected to an electrical ground. The ground wire (green/yellow) in the instrument power cable must be connected to the installation electrical ground system.

  • Page 8: Installation

    3 Installation Supply Connections Before applying power to the instrument, ensure that the voltage selector on the rear panel is correctly set for the intended supply voltage. If necessary, open the voltage selector panel using the slot provided, withdraw the voltage selector and replace it in the correct orientation for the intended voltage.

  • Page 9: Auxiliary Port Connections

    Users familiar with Oxford Instruments earlier Helium Level meters models HLM2 and 4016 should note that the direction of current flow through the helium level probe is reversed with respect to these instruments. The top of the probe is now positive, where it was previously negative.

  • Page 10: Relay Contact

    The contacts to be linked are pins 7 and 14 of the PARALLEL I/O socket on the IPS family of Oxford Instruments Power Supplies. (On the earlier PS120-10 and PS120-3 power supplies, the same pin connections are used but...

  • Page 11: Analogue Outputs

    A pair of wires should be run from these pins to the COMMON and NORMALLY open contacts (i.e. the front and middle terminals) of the relay to be used. Normally this will be the relay associated with the channel being used for Helium level measurement. However if a helium autofill system is also in use, another relay may be used for rundown.

  • Page 12: The Oxford Instruments Isobus

    None The Oxford Instruments Isobus A unique feature of ILM 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).

  • Page 13: The Gpib To Isobus Gateway

    GPIB without themselves requiring GPIB interfaces. This can enable other Oxford Instruments products, for which an internal GPIB interface is not available, to be linked. It offers the additional advantage of optical isolation between these instruments and the GPIB.

  • Page 14: Operation

    4 Operation Front Panel Controls The front panel controls are grouped together in logically related blocks. POWER The main ON/OFF switch. A green lamp illuminates whenever the instrument is switched ADJUST The red RAISE and LOWER buttons provide the main means of adjusting any parameter. In ILM their main use is for adjusting the display reading during the configuration and calibration process.

  • Page 15: First Time Operation

    The SILENCE control button has a number of secondary SELECT functions which are obtained by pressing this button whilst one or more other buttons are held depressed. If SILENCE is pressed whilst both RAISE and LOWER are held in, ILM enters the TEST mode (see Section 9).

  • Page 16: Err" Display

    "Err" Display If no probe is plugged into a channel which has been configured to be in use, the display will show a steady "Err" display. The same display will be produced to indicate a fault in the probe, its wiring, or the ILM itself. In the case of a nitrogen probe, if the display flashes between "Err"...

  • Page 17: Setting The Default Calibration

    With the cryogen at a known level near zero, the 0% button should be pressed and RAISE and LOWER used so that the known level is displayed. The process is should then be repeated at a known level near full, using the 100% button. It is often convenient to set the 0% point to exactly 0 when liquid starts to collect during the cryostat cooldown and to set the 100% point to exactly 100% when the reservoir is completely full.

  • Page 18: Storing Calibration And Other Power-Up Defaults

    In both cases when the two buttons are pressed together the display will show "dEF" to indicate that default conditions have been set. Storing Calibration and other Power-Up Defaults Whenever any data has been changed, which is intended to be retained after power down, this must be deliberately STORED.

  • Page 19: Auto-Fill And Alarms

    5 Auto-Fill and Alarms Level Thresholds There are three threshold levels associated with each channel. These are used to control an automatic filling operation, or to sound an audible alarm or de- energise a magnet in the event of low cryogen level. The three levels are called FULL, FILL, and LOW, with FULL normally being the highest level and LOW the lowest.

  • Page 20: Automatic Rate Switching

    An alternative method of controlling filling is to use a motorised needle valve. This may for example be used for filling a small reservoir from a main helium bath. ILM supports the use of a small stepper motor to drive such a needle valve. The motor is connected to the auxiliary port.

  • Page 21: Audible Alarm

    Audible Alarm When the cryogen level falls below the LOW level, ILM is able to sound a built-in audible alarm, to alert the operator to the low level. At the same time an external signal is available (relay 4) which may be used to drive a remote alarm. When the alarm sounds, pressing the SILENCE button will stop the noise, but leave the ALARM lamp lit until the cryogen is replenished above the LOW level.

  • Page 22: Remote Operation

    ILM may be remotely operated by means of its RS232 or GPIB interface. This allows a computer to interrogate the instrument. For compatibility with other Oxford Instruments products, a mode is available allowing the computer to control the instrument and initiate sampling pulses.

  • Page 23: Numeric Parameters

    Use with Oxford Instruments ISOBUS The Oxford Instruments ISOBUS allows a number of instruments to be driven in parallel from a single RS232 port on a computer, using a special cable assembly.

  • Page 24: The Gpib Interface

    It should be used with caution however, since all responses are suppressed, including the "?" error response. Thus the computer has no way of knowing if a command has been received or even if the instrument is connected. If a command is to be addressed to a specific instrument, but no reply is required, it is permissible to use "$"...

  • Page 25: Sending Commands Via The Gpib

    6.6.1 Sending Commands via the GPIB Commands sent via the GPIB follow exactly the same syntax as for the RS232 interface. Commands must be terminated by a Carriage Return <CR> character, (ASCII 13). A Line Feed <LF> may be sent if desired but is not needed and will have no effect. (Your GPIB controller may send <CRLF>...

  • Page 26: Use Of The Service Request Line

    ILM updates the status byte every millisecond. Thus if the status byte is read within 1mS of reading data from the interface, the MAV and BAV bits may not yet have been cleared, even though all available data has been read. If these bits are found to be unexpectedly set immediately after a data read, a second read of the status byte at least 1mS later will confirm whether there really is data remaining.

  • Page 27: Compatibility With Ieee-488.2

    This allows one or more other instruments to be connected to the first instrument using the Oxford Instruments ISOBUS. These may share the benefits of being controlled by the GPIB controller, whilst at the same time enjoying the advantages of optical isolation provided by ISOBUS.

  • Page 28: Command List

    7 Command List A brief summary of the available commands is given below. Fuller details are given in the following section. Commands fall into 3 categories: MONITOR COMMANDS which are always recognised. CONTROL COMMANDS which are only recognised when in REMOTE control. SYSTEM COMMANDS which are only recognised after receipt of the correct "UNLOCK KEY".

  • Page 29: Command Syntax

    The control command sets ILM into LOCAL or REMOTE. It is provided primarily for compatibility with other Oxford Instruments products, so that all may be switched into REMOTE simultaneously with a $Cn command. At power up ILM defaults to the C0 state.
  • Page 30 Unnnnn COMMAND The UNLOCK command allows access to the SYSTEM commands. This set of commands are intended for diagnostic and configuration purposes and have the power to erase or modify the contents of the memory. The U command must be sent with the correct KEY parameter before these commands may be used.

  • Page 31: Interpreting The Status Message

    Fnn COMMAND The FRONT PANEL DISPLAY command sets which channel will be displayed on the channel 1 display for diagnostic purposes. The parameters which may be displayed are as listed for the "R" command above. Gnnn COMMAND Allows the needle-valve stepper motor (if fitted) to be set to a new position. In ILM the absolute position of the needle valve is not defined, so this command is unlikely to be of use in normal operation.
  • Page 32 Relay Status consist of a single pair of Hexadecimal digits. This again is best thought of as an 8 bit binary number where the bits each have a separate significance. The significance of the individual bits within the message is given in the tables and examples which follow.

  • Page 33: Example Sequence

    Bit 0 In Shut Down State Bit 1 Alarm Sounding (Relay 4 Active) Bit 2 In Alarm State (Sound may have been SILENCED) Bit 3 Alarm SILENCE prohibited * Bit 4 Relay 1 Active Bit 5 Relay 2 Active Bit 6 Relay 3 Active Bit 7 Relay 4 Active...
  • Page 34 X210S030000R00 Helium has been switched to FAST & current is on for a pulse. X210S020000R00 Pulse is complete. Helium remains in FAST rate. X210S0A0000R00 Still in FAST. Level has fallen below 90% (FULL threshold). X210S0C0000R00 Operator has switched Helium back to SLOW. X210S1A0000R10 Level has fallen below 20% (FILL threshold).

  • Page 35: Configuration And Test Mode

    9 Configuration and Test Mode Use of Test Mode Test mode is provided to give an easy means of testing the ILM hardware and to allow it to be configured for specific applications. Test mode gives a menu of options arranged in the logical order for testing, configuring and calibrating a new instrument.

  • Page 36: Test T.03 Setting The Gpib Address

    Test t.03 Setting the GPIB Address The GPIB interface (if fitted) is normally supplied set to a GPIB address of 24. On accessing Test 3, the display will now show G.nn where nn is the current GPIB address. Use RAISE and LOWER to display the desired new address, then press SILENCE to select it.

  • Page 37: Test T.06 Calibrating The Current Sources

    The configuration is specified by a number in the range 0 to 255. The number is made up of 4 parts, as follows. Just one option should be selected from each part. The final number is obtained by adding the numbers for the 4 parts. OPERATING MODE 0 - Channel not in use 1 - Channel used for Nitrogen Level...

  • Page 38: Test T.07 Setting Probe Active Length

    When t.06 is selected the display for the first Helium channel will show "ICAL" and both FAST and SLOW will light, indicating that current is flowing through the probe. For this test a current meter should be connected in place of the probe. RAISE and LOWER may be used to adjust the actual current flowing through the meter till this reads 100 mA.

  • Page 39: Test T.09 Setting Helium Probe Pulse Widths

    Unless you have been advised otherwise by Oxford Instruments you should assume that your probe will not require a pre-pulse. In which case, both the pre- pulse current and the pre-pulse width should be set to zero.

  • Page 40: Test T.12 Setting Stepper Motor Operating Mode

    SILENCE will show the nominal resistivity in ohms per metre, which may be adjusted by means of RAISE and LOWER. For the normal Oxford Instruments probes, this should be set to approximately 166 ohms per meter. For long probes, using a thicker probe wire, the nominal setting is 61.2 ohms per metre.

  • Page 41: Servicing

    10 Servicing 10.1 Safety This section of the manual contains information intended to help a qualified service engineer diagnose faults on the ILM. Some of the test procedures involved require operation of ILM with the covers removed. This can expose the engineer to the risk of contacting lethal voltages.

  • Page 42: Reset Procedures

    When a Helium probe is in use, the probe voltage is filtered and fed to the V/F converter U120. This generates a frequency in the range 5kHz to 65kHz for normal probe operation, which is fed via opto-isolator U121 to the digital circuitry where it is counted. The reference voltage for U120 is fed via the VLOW to ILOW link in the probe.

  • Page 43: Two Button Reset

    10.3.2 Two Button Reset The main RAM content is always restored from the EEPROM at switch on, so that in many cases it may be possible to recover from problems by simply switching off and switching on again. If this fails to correct the problem, bad data may have been written to the EEPROM.

  • Page 44: In Case Of Difficulty

    11 In Case of Difficulty This section indicates some of the more common pitfalls and operator errors. Display shows "Err" in normal use No probe is plugged in to the channel, or the probe is defective. If "Err" flashes, in the case of a nitrogen probe, the probe inner and outer tubes are shorted.

  • Page 45: Specification

    12 Specification CHANNELS 1, 2 or 3 ILM201 1 x Nitrogen ILM210 1 x Helium ILM211 1 x Helium, 1 x Nitrogen ILM220 2 x Helium ILM221 2 x Helium, 1 x Nitrogen SENSING METHOD Helium Superconductive Wire Nitrogen Capacitance PROBE LENGTH Helium 1.4 metres (standard wire)
  • Page 46 IEEE-488 INTERFACE Optional Internal Interface ADDRESS RANGE 1 to 31 CAPABILITY IDENTIFICATION CODE SH1 AH1 T6 L4 SR1 RL0 PP0 DC1 DT0 C0 E1 CONNECTORS POWER IN IEC 3 pin PROBE INPUT 3 off 9 way D socket AUXILIARY I/O 15 way D socket RS232 25 way D socket...

  • Page 47: Quick Reference Guide

    13 Quick Reference Guide 13.1 Panel Controls and Lamps RATE Toggle between FAST and SLOW. Sample immediately on entry to FAST. (Helium Level Only). FAST/SLOW Light to show FAST or SLOW sampling rate. BOTH lit during pulse. (Helium Level Only). Calibrate reading near zero, using RAISE and LOWER.

  • Page 48: Interpreting The Status Message

    Set Communication Protocols Normal Send <LF> after every <CR> Send Reading for parameter nn. (nn as for t.04 in "Test Mode Menu") Set Channel n to Slow sample rate Set Channel n to FasT sample rate Unlock for memory load etc. (See manual) Unnnnn Send Version Wnnnn...

  • Page 49: Test Mode Menu

    and where uu, vv and ww are pairs of Hexadecimal digits defining Channel Status. Each pair represents an 8 bit, binary number, where the bits have the following significance (Bit 0 is LS bit): Bit 0 Current flowing (Including pre-pulse) Bit 1 In FAST rate Bit 2...
  • Page 50 t.05 CONFIGURE "CFG" each Channel in turn. Specified by a number in the range 0 to 255, made up of 4 parts. The configuration number is obtained by adding the 4 parts. Operating MODE Channel not in use Channel used for Nitrogen Level Channel used for Helium Level (Normal Pulsed Operation) Channel used for Helium Level (Continuous Measurement) Action on FILL condition...
  • Page 51 t.12 Set Needle Valve stepper motor operating mode. t.13 Set Needle Valve position manually, for leak testing. t.14 Set wire resistivity (ohms/metre) for helium probes...

  • Page 52: Circuit Diagrams

    CNC1002 (2 sheets) DISPLAY BOARD CNC2002 (7 sheets) MAIN BOARD CNC5102 (1 sheet) NITROGEN PROBE CNC5202 (1 sheet) HELIUM PROBE CNC6802 (1 sheet) 2 CHANNEL RECORDER OUTPUT LEAD CVA0002 (1 sheet) OXFORD INSTRUMENTS ISOBUS CABLE CVG0102 (1 sheet) GPIB INTERFACE...

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