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NM21283A-A

25

P

ART

2

Sensor operation principles

This part describes the operation principles of a SQUID sensor and
electronics. It also contains a detailed description how the sensors are
tuned manually. Manual tuning is needed in the initial setup of the
device and when the automatic tuning fails for some reason.

Reading of this chapter is recommended for all users who want to
understand the operation of the device. Understanding of the operation
is necessary for the maintenance personnel and when reading the third
part describing the advanced features of the tuning program.

Содержание NM21283A

Страница 1: ...Sensor Tuner User s Guide Software Version 3 0 for Elekta Neuromag March 2005...

Страница 2: ...e related software including but not limited to the implied warranties of merchantability and fitness for a particular purpose Elekta Neuromag Oy shall not be liable for errors contained herein or dir...

Страница 3: ...3 Basic tuning operations 11 3 1 Measuring the sensor noise level 11 3 2 Fine tuning 12 3 3 Resetting channels 13 3 4 Heating sensors 13 3 5 About saving and loading settings 14 3 6 Noise display 15...

Страница 4: ...ypical sensor problems 39 Part 3 Advanced features Chapter 8 Basic measurements 43 8 1 Setting the expert level 43 8 2 Selecting and running jobs 44 8 3 Measurement parameters 45 8 4 View modes 46 8 5...

Страница 5: ...7 11 6 Updating the power up settings 58 11 7 Synchronizing Janitor 59 11 8 Using SSP 59 Chapter 12 Description of the menus 61 12 1 File Menu 61 12 2 Job Menu 62 12 3 Parameters Menu 63 12 4 Commands...

Страница 6: ...iv NM21283A A...

Страница 7: ...level being used The lowest level 0 allows noise measurements and automatic fine tuning of the system The expert level 1 allows more complicated measurements and setting of various parameters affectin...

Страница 8: ...2 NM21283A A...

Страница 9: ...f the SQUID tuning program It contains information about the functionality available in the lowest expert level 0 This allows measuring white noise level of all channels and automatic fine tuning Read...

Страница 10: ...4 NM21283A A...

Страница 11: ...an initiate different kinds of operations by clicking corresponding button in a menu When a button within the menu is pressed and the mouse button is released the corresponding action will be executed...

Страница 12: ...on point with mouse button 2 Selecting some text by button 1 and pasting it in some other place by pressing button 2 saves often a lot of time compared to entering the same text from keyboard Copying...

Страница 13: ...w name in this field and press ok button For details of editing text fields see Using text fields on page 5 To select a file that already exists double click the name of the file in the right selectio...

Страница 14: ...1 User interface basics 8 NM21283A A...

Страница 15: ...g about the already running program In such a case you should answer OK to stop the new one and find out who is running the program It is possible that you get this message even if there is no other i...

Страница 16: ...a button which shows the version information about the program No online help is currently available 2 3 Ending a session To exit the program select Exit from the File menu This menu is inactive gray...

Страница 17: ...an be initi ated In this case one must exit the tuner stop the normal acquisition measurement and then restart the tuner again Warning Acquisition program can not perform measurements if the tuner is...

Страница 18: ...ut saving and loading settings on page 14 Contact your administrator to find out the correct tuning file When the channels seem to work properly but the noise level is higher than normally running the...

Страница 19: ...lms trap magnetic flux Strong magnetic field can penetrate the film destroying the superconductivity from a small patch of the film so that the field can go through it Typically the impurities in the...

Страница 20: ...cial situations like using the device just after helium filling or when the helium level is very low In normal conditions one good setting file should be enough If the automatic fine tuning of the sys...

Страница 21: ...ult scale should be good in normal situations If you need to change the y scale of the display use the control buttons in the lower right corner of the display The buttons available are following Note...

Страница 22: ...a diometer channels and magnetometer channels are shown separately Gra diometers with red bars and magnetometers with blue bars assuming default colors The lower bar is always in front of the higher o...

Страница 23: ...ding settings on page 14 Heat suspicious or all sensors See Heating sensors on page 13 Try tuning even if all previous fail system may be just in some non typi cal state like just after powering up th...

Страница 24: ...y clicking with the left mouse button any particular measurement time The bias off set and gate values are shown in the information area This is especially useful if the tuning has for some reason fai...

Страница 25: ...opped up by selecting the menu button Parameters Active channels The active channels dialog is shown in Figure 4 1 The upper part of the dialog contains a check box for each channel The boxes are labe...

Страница 26: ...eas ily The buttons that alter the selections are Set All Activate all channels Reset all Deactivate all channels Reset mags Deactivate all magnetometers Reset grads Deactivate all gradiometers So if...

Страница 27: ...of the infor mation in the file is discarded See also About saving and loading settings on page 14 Save tunings This button saves all currently active parameters into a file It also sets the current...

Страница 28: ...heats all sensor units See Heating sensors on page 13 Show all histories Selecting this button will show a graph containing noise histories of all channels superimposed on top of each other See Viewi...

Страница 29: ...ged to a suitable default value when a job is selected from the Job menu so it is not needed often Noise Select the white noise level to be shown on the graphics area Noise Histogram Select the white...

Страница 30: ...5 Description of the menus 24 NM21283A A...

Страница 31: ...uned manually Manual tuning is needed in the initial setup of the device and when the automatic tuning fails for some reason Reading of this chapter is recommended for all users who want to understand...

Страница 32: ...26 NM21283A A...

Страница 33: ...il that gathers the flux and a signal coil that couples it into the SQUID This has the advantage of increasing the field sensitivity by increasing the effective sensor area magnetic flux equals field...

Страница 34: ...tage bias voltage over the SQUID and mea sure the current through the device Vectorview electronics uses this volt age bias mode of operation Figure 6 2 depicts the current vs voltage characteristics...

Страница 35: ...ious signals to the SQUID The bias voltage is set with the help of an operational amplifier which is also employed to amplify the SQUID signal The operational amplifier tries to keep the voltage acros...

Страница 36: ...n section 6 3 To linearize the periodic current vs flux characteristics a so called flux locked loop is employed The output of the SQUID is integrated and fed back to the feedback coil When the feedba...

Страница 37: ...cquisition workstation is called Collector Normally these pro grams are not used directly but through either the acquisition program or the tuning program 6 3 Optimal point of operation The optimal po...

Страница 38: ...where the curve crosses zero line The noise of the SQUID depends in general on the value of the input flux It has been found experimentally that for Vectorview SQUIDs the minimum noise is most often...

Страница 39: ...al tuning cycle If you encounter degraded performance try first heating see Heating sensors on page 13 then loading a previously loaded setting file that corresponds most closely to the actual Helium...

Страница 40: ...d now be on the x y display 7 4 Measuring flux to current curves using Tuner You can also use Tuner to measure the I curves To do this you must be using expert level 1 To change the expert level see S...

Страница 41: ...to deliver signal levels which saturate the inputs of DSP boards enough to cause them to fold the signals If the signal is very noisy and changes to opposite direction than normally when bias or offse...

Страница 42: ...plateau on the bottom appears increase the bias setting until it has completely disappeared see curve You may decrease the bias further by one or two units to ensure sta bility The current vs flux cha...

Страница 43: ...dicat ing that the gate voltage has been increased too much Decrease the gate voltage step by step back until the hump has completely disappeared and the current vs flux characteristics looks again sm...

Страница 44: ...optimum try the following technique lower the gate voltage until you see the noise to increase clearly Then go back by increasing the gate voltage until the extra noise is gone Finally try adjusting t...

Страница 45: ...ting the heating a couple of times or try changing the heating time temporarily to 2 seconds Sometimes the current v s flux curve is tilted that is one end of the curve is higher than the other as if...

Страница 46: ...7 Manual tuning 40 NM21283A A...

Страница 47: ...automatic tuning of several parameters Features described here are intended for maintenance personnel and require that the user expert level is set to 1 For the basic automatic fine tuning process for...

Страница 48: ...42 NM21283A A...

Страница 49: ...e noise levels Also the dc and line fre quency level of disturbances are measured These can be viewed manually or used in automatic noise level tuning FFT Measure the spectrum of the sensor signal Thi...

Страница 50: ...s already selected The text on the start button changes according to the job so that you can identify the currently selected job To start a measurement press the start button to stop it press the stop...

Страница 51: ...he following sections describing a job also describe the associated parameters For a complete list of all parameters see Appendix B The parameters can be adjusted using dialogs that can be accessed th...

Страница 52: ...hi job measures the flux versus current characteristics of all sen sors It can average several measurements and the data is arranged so that it is possible to estimate factors like feedback voltage co...

Страница 53: ...have been normalized using the nominal modulation depth at the nominal operating point For setting resetting the nom inal operating point see Operating point parameters on page 53 In this view all bar...

Страница 54: ...iew shows a noise histogram DC levels This mode shows the dc levels of the channels DC level histogram This mode shows the DC levels as a histogram Line freq levels This mode shows the level of the fu...

Страница 55: ...trolled by parameter FFTaverages It is pos sible to apply SSP noise reduction to the data before calculating the FFT in order to diminish the contribution of external disturbances The last four parame...

Страница 56: ...te noise level red and low frequency noise level black All noises are displayed in RMS per Single channel view shows the RMS spectrum of the selected channel 8 8 Signal This job measures a sample of t...

Страница 57: ...t specified level 9 1 Noise level based tuning To optimize the noise level of the sensors Tuner provides procedures to automatically tune the operating point parameters All three routines are similar...

Страница 58: ...defined criterion The fraction parameter describing the level at which the I curve crosses the zero level is adjusted so that it matches the value defined for the nominal operating point Only the offs...

Страница 59: ...the current operat ing point and the nominal operating point The first one is naturally the current state of the sensors the second one is the correct operating point that was either loaded from a st...

Страница 60: ...es for the flux quantum sizes Note that the dV dB value is not needed in any of the current optimization of characterization routines and that the dV dO value is independent of the operating point so...

Страница 61: ...istics 10 NM21283A A 55 10 4 Measuring gate curves To measure the noise as a function of the gate value setting with fixed bias and offset settings select Job Scan gate from the menus and wait until t...

Страница 62: ...g parameters there are two options loading of parameters of a single channel and saving and loading of some selected parameters only The normal File Save tunings operation saves all parameters except...

Страница 63: ...Select File Revert to previous o p from the menus 11 5 Creating start up files To make the tuner run easily and properly one should have two start up files properly set When the program is started it...

Страница 64: ...by issu ing a menu command During the initial loading the settings of the mag netometer are not changed Only the variables defining the correct operating point are changed When the settings are loade...

Страница 65: ...mmand from the menus In normal situation this command just refreshes all registers in the dewar top electronics so it should not cause any harm to issue the command 11 8 Using SSP Noise reduction base...

Страница 66: ...11 Miscellaneous 60 NM21283A A...

Страница 67: ...o load some other information use Load Load selected params button See About saving and loading settings on page 14 Save tunings This button saves all currently active parameters into a file It also s...

Страница 68: ...tton to stop the program A verification is required to really stop the program See Ending a session on page 10 12 2 Job Menu This menu contains buttons that define the operation that should be per for...

Страница 69: ...V curve Select measurement of current versus voltage curves Scan gate Select measurement of noise versus gate value 12 3 Parameters Menu This menu contains buttons that pop up various dialogs that ena...

Страница 70: ...ommands that can be executed Reset electronics Pressing this button causes resetting of all active channels See Resetting channels on page 13 Heat sensor Heat a single sensor See Heating sensors on pa...

Страница 71: ...fraction parameter Worst Noise Search the channel with largest white noise Weird Phi0 Search the channel whose measured flux quantum differs most from the average Next Search next channel This button...

Страница 72: ...ee Measuring the sensor noise level on page 11 Noise histogram Select the white noise level histogram to be shown See Measuring the sensor noise level on page 11 FFT Select the spectrum of the signal...

Страница 73: ...Show history of bias value settings Offset history Show history of offset value settings Gate history Show history of gate value settings 12 7 Help Menu The help menu contains only one button that di...

Страница 74: ...is option are tune fine tune noise i phi manual tune fft gate bias offs modu signal defs filename Define the name of the file containing the system parameters default values static filename Define the...

Страница 75: ...hat describe the structure of the measurement system and its environment The parameters are shown in Table B 2 class parameter name type description system SysType string Type of the device system Lin...

Страница 76: ...tude V measurement FuncFreq float Function generator frequency Hz measurement WuFuInterval integer reserved Table B 2 I Phi measurement parameters class parameter name type description measurement Noi...

Страница 77: ...white noise interval Hz measurement FFTwhiteEnd float End of the white noise interval Hz class parameter name type Table B 4 FFT measurement parameters class parameter name type description measuremen...

Страница 78: ...lingTime integer Settling time between measurements measurement GateFork integer reserved Table B 7 Gate scan parameters class parameter name type description state OpHeLevel integer Helium level at t...

Страница 79: ...tring Low frequency histogram fill color preference BandColor string White noise color for gradiometers preference BandColor2 string White noise color for magnetometers preference AliasedColor string...

Страница 80: ...eference DispScaleFFT float FFT plot scale preference DispOffsFFT float FFT plot offset preference DispScaleSign float Signal plot scale preference DispOffsSign float Signal plot offset Table B 11 Sca...

Страница 81: ...t used by the program class parameter name type description obsolete VErrorNBins integer obsolete obsolete VErrorBinWidth float obsolete obsolete MarkerStyle integer obsolete obsolete TuneBand float o...

Страница 82: ...is a tuning program for Elekta Neuromag Vectorview and Neuromag System devices The program was developed from program tune version 2 0 which is used with Neuromag 122 systems Due to such historical r...

Страница 83: ...Histogram changing bin width 16 Histograms changing resolution 16 viewing noise level 16 I I Phi measurement 46 I V characteristics 28 I V curve 54 L Loading settings 14 56 Locking channels 19 M Magne...

Страница 84: ...R Resetting channels 13 Reverting operating points 57 S Saving settings 14 15 56 58 Searching 56 Selecting channels to be shown 18 job 44 view of all channels 18 Sensor operation 27 Setting expert lev...

Страница 85: ...34 To measure I Phi curves using Tuner 34 To measure the approximate noise level using Squiddler 35 To measure the I V curve of the SQUIDs 54 To measure the operating point derivative information 54...

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