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Sensor Tuner

1. Specific measurement results can be selected for viewing from the View menu The displays that are associated to each measurement mode are listed in the description of each mode 8 5 I Phi measurement The I Phi 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 corresponding one o modulation depth etc If these characteristics are needed for manual tuning purposes use Man ual tune instead It performs the same measurement without any averag ing showing the raw x y data The basic I Phi job is rarely used manually however the measurement is used as a building block in several other jobs so that adjusting the parameters in I Phi measurements does affect sev eral other jobs The parameters affecting the I Phi measurements are shown in table Table 8 1 Parameter Type Description AveLength integer Number of x bins in x y trace curves used in averages NumAverages integer Number of averages taken TuneSfreq float Sampling frequency used Hz FuncAmp float Excitation amplitude V FuncFreq float Excitation frequency V Table 8 1 Parameters affecting I Phi measurements NM21283A B Basic measurements g The I Phi measurement results can be displayed using following view modes I Phi curve This mode shows the I curve
2. 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 This gives more detailed information about the noise compared to the Noise measurement but is slower Spectra can be shown on a display and noise values in selected bands can be printed Signal Measure a sample of the time trace of the sensor signal This mea surement can be used to get a sample of signal to visually examine its quality Setting the expert level NM21283A B In order to use features described in this part the expert level must be set to 1 The setting defaults to zero but it is saved in the preferences of the user so that once it has been changed it 1s kept from session to session To change the expert level setting 1 Select File gt Preferences from the menu A dialog box containing all the values regarded as preferences is popped up 43 H Basic measurements 44 2 Change the entry in the text field expertLevel and press RETURN After changing the level new entries should appear in to the prefer ences dialog Also some new menus will appear 3 Close the dialog by pressing Close The rest of the parameters in preferences settings dialog are explained in Appendix B 8 2 Selecting and running jobs Before staring an operation you need to select what to do You can select the operation from the Job menu The jobs are describ
3. levels This mode shows the level of the fundamental frequency of the line frequency Line freq level histogram This mode shows the line frequency levels as a histogram 48 NM21283A B Basic measurements g 8 7 FFT measurement The job FFT is for measuring power spectra of the channels This can be used to examine the external disturbances and noise characteristics in more detail compared to the Noise measurement The spectrum estima tion uses a Hanning window and non overlapping averaging The parameters affecting the FFT measurements are shown in table below Parameter Type Description TimeBufSize integer Time buffer length samples FFTsize integer FFT transformation length samples FFThpf float High pass filter setting Hz FFTIpf float Low pass filter setting Hz FFTsfreq float Sampling frequency Hz FFTaverages integer Number of averages FFTssp Oorl IsSSP used FFTlowStart float Start of low freq estimation range Hz FFTlowEnd float End of low freq estimation range Hz FFTwhiteStart float Start of white noise estimation range Hz FFTwhiteEnd float End of white noise estimation range Hz Table 8 3 Parameters affecting FFT measurements The Time buffer size defines the length of the time trace that is actually measured From the beginning of each time trace FFTsize samples are taken and transformed into Spe
4. 1121 1122 v 1123 1131 1132 1133 1141 1213 v 1221 v 1222 v 1223 1231 1232 1233 v 1241 1313 v 1321 v 1322 v 1323 1331 1332 1333 A 1341 1413 1421 v 1422 v 1423 1431 1432 1433 v 1441 1513 v 1521 v 1522 v 1523 1531 1532 1533 v 1541 1613 1621 v 1622 v 1623 1631 1632 1633 v 1641 1713 1721 v 1722 v 1723 1731 1732 1733 1741 1813 v 1821 v 1822 v 1823 1831 1832 v 1833 v 1841 1913 1921 1922 v 1923 v 1931 v 1932 v 1933 ET RI 2013 v 2021 v 2022 v 2023 v 2031 v 2032 v 2033 v 2041 2113 2121 2122 v 2123 v 2131 v 2132 v 2133 v 2141 2213 v 2221 v 2222 v 2223 vi 2231 v 2232 v 2233 v 2241 2313 v 2321 v 2322 v 2323 v 2331 v 2332 v 2333 v 2341 2413 2421 v 2422 v 2423 v 2431 v 2432 v 2433 v 2441 2513 v 2521 v 2522 v 2523 v 2531 v 2532 v 2533 v 2541 2613 v 2621 v 2622 v 2623 v 2631 v 2632 v 2833 v 2641 Set all Reset all Reset mags Reset grads Cancel NM21283A B Figure 4 1 19 n Troubleshooting 20 At the bottom of the dialog there are some extra buttons in addition to the standard ones By using the you can set or reset large set of channels eas ily The buttons that alter the selections are Set AII Activate all channels Reset all Deactivate all channels Reset mags Deactivate all magnetometers Reset grads Deactivate all gradiometers So if you want to tune only one particular channel press Reset al
5. 2 only Select measurement of noise versus gate value 12 3 Parameters Menu This menu contains buttons that pop up various dialogs that enable the modification of parameters used in various tasks The parameters are described briefly in Appendix B Active channels This button pops up a dialog that allows you to set the channels that are affected by the tuner If a channel is not active it is not modified and it set to a passive state to minimize its effect on other chan nels See Tuning selected channels on page 18 System Parameters Open an editor for system parameters I Phi measurements Open an editor for I Phi measurement parameters See I Phi mea surement on page 46 Noise measurements Open an editor for noise measurement parameters See Noise mea surement on page 47 FFT measurements Open an editor for spectrum measurement parameters See FFT measurement on page 49 Signal measurements Open an editor for signal measurement parameters See Signal on page 50 Tuning settings Open an editor for tuning parameters Bias scan Level 2 only Open an editor for bias scan parameters See Measuring and using current voltage characteristics on page 54 Gate scan Level 2 only Open an editor for gate scan parameters See Measuring gate curves on page 55 64 NM21283A B Description of full menus 12 12 4 Commands Menu This menu contains buttons for various comm
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7. B 12 2 Job Menu This menu contains buttons that define the operation that should be per formed The job is not executed immediately These buttons only select which job will be run when the start button is pressed For more detailed descriptions of the jobs see Chapter 8 and Chapter 9 I Phi Select measurement of flux to current characteristics Noise Select white noise measurement This gives less information but is faster than a measurement of noise spectrum It also provides the level of line frequency disturbance and the dc levels of all the chan nels FFT Select FFT measurement that gives the spectrum of the signals This gives information about the noise as a function of frequency but it is slower than a measurement of white noise only Signal Measure signal samples Tune Select automatic tuning of all operating point parameters This ver sion uses larger steps than the fine tuning below Faster than the fine tuning but not as robust Tune fine Select the automatic tuning of all operating point parameters using small steps Tune gate Select automating tuning of gate settings only Tune offs Select automatic adjustment of offset values Manual tune Select manual tuning mode Meas derivatives Select measurement of operating point derivative information Meas I V curve Level 2 only Select measurement of current versus voltage curves 63 12 Description of full menus Scan gate Level
8. If there are helium try loading a known tuning file If this does not help manual tun ing is needed If just some channels are noisy try heating the channels See Heating sensors on page 13 4 2 Viewing noise history of a channel NM21283A B If some particular channel is misbehaving in tuning you can study the noise values of a channel in previous noise measurements e g how the 17 n Troubleshooting 18 noise evolved during the tuning process To do this select one channel to be displayed Selecting a channel can be done in three ways By entering the channel number into the channel number box of the operating point controls The number should be the ordinal number not the number in the sensor name See Figure 2 1 Byinserting the channel name into the channel name box of the operat ing point controls See Figure 2 1 By clicking the noise bar of the channel in the noise display with the left mouse button while pressing the CTRL key The display will now show the name of the channel and a curve that indi cates the noise level at each noise measurement made during the session You can scale the noise history display same way as the bar display See Noise display on page 15 To change back to view all channels 1 Enter 0 into the channel number box or 2 Click anywhere in the display with right mouse button having the CTRL button simultaneously pressed down You can also view the previous operat
9. for the current state from last measurement performed if any and for the nominal operating point from the state last loaded or saved from to a parameter file The parameters shown in the channel info dialog are Channel Running channel number of the sensor Bias Bias setting Offs Offset setting Gate Gate setting Modulation Modulation depth volts in input Phi Flux quantum size volts in excitation line Fraction Where I curve crosses the zero line 0 lower edge 100 higher edge dV dB Voltage change per bias adjustment unit in I mode dV dO Voltage change per offset adjustment unit in I mode Bias drift Not used 53 E Measuring characteristics 54 Offs drift Not used He level helium level Operating point settings modulation depth and fraction are updated in every I dp measurement Helium level is automatically checked when the program starts The flux quantum sizes can be estimated after a I mea surement by selecting Commands gt Estimate phi0 from the menus The derivative information must be measured with a separate routine described in next section 10 2 Measuring derivative information To measure the operating point derivative information 1 Check that the current operating point is correct 2 Check that all I traces are on the screen and none of them is very near saturation near highest or lowest signal level available 3 Select Job Meas derivatives from t
10. off when the sensor is later returned to its normal state NM21283A B Basic tuning operations E NM21283A B 3 3 3 4 Warning Tuning for excessively long times 5 min does not make the tuning better Instead if the noise level is limited by something else than SQUID noise the tuning settings may drift to unstable values Resetting channels The SQUID sensors are operated in so called flux locked mode See SQUID electronics of Vectorview on page 29 In some situations the electronics is not capable following the signal and the output gets satu rated This can be due to very strong signals e g environmental low fre quency drift or sharp transients To get the sensor working again the integrator in the feed back loop and the zeroing mechanism high pass fil ter need to be reset Saturated channels that need to be reset are repre sented as small negative bars in the noise display To reset all channels 1 Select Commands gt Reset channels from the menus Heating sensors The coils and the SQUIDs in a sensor unit contain very thin superconduct ing film Sometimes when the sensor is exposed to strong relative to the signals measured magnetic field these films 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 films cause these holes to stick at some fix
11. personnel so that the expected performance is known and possible changes in the sys tem can be detected To load tuning settings into tuner and magnetometer 1 Select File gt Load tunings from the menu A dialog will pop up 2 Ifthe file suggested by the dialog is the one you want to load press OK to load the file Otherwise press Load other to pop up an ordinary file selection box and use it to select the file you want to load See Using file selection boxes on page 6 NM21283A B Basic tuning operations E To save tuning settings into a file 1 Select File gt Save tunings from the menu A dialog will pop up 2 If the file name suggested is the one into which you want to save the settings press OK if not press Save elsewhere and use the appear ing file selection box to select the file If you get an error message Could not get clean snapshot bad params at ch lt number gt this means that all parameters of the tuner are not set properly However you can save the settings anyway if you just need to save the regular working point parameters To get rid of this message contact your administrator to set up the start up files to contain all required information 3 6 Noise display NM21283A B The tuner displays normally bar diagram showing the noise level of all channels During fine tuning this display shows the noise after each step The default scale should be good in normal situations If you need to
12. the electronics cabinet by the shielded room The analog part consists of preamplifiers and circuits that generate the bias offset and gate voltages These are on top of the dewar All the signals between the two parts are converted from analog regime to digital and vice versa on the signal processor boards The operation of both analog and digital parts are controlled by the real time computers of the system The program controlling the analog part is called Janitor and the program controlling the signal processors and data stream to acquisition 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 NM21283A B The optimal point of operation of the SQUID is the combination of bias offset and gate settings that gives the minimum noise The noise depends on all those parameters Normally the voltage bias that gives the maximum modulation depth also gives minimum noise The current vs flux characteristics should be above superconducting state everywhere no visible plateaus For stable opera tion the adjustment should not be just on the edge but rather slightly above In some rare cases it may happen that minimum noise is achieved at a higher bias this is usually the case if the current vs flux characteris tics is not smooth Then it may be necessary to adjust the bias higher Note that the shape of the curr
13. tion of parameters used in various tasks 21 H Description of the menus Active channels This button pops up a dialog that allows you to set which channels are affected by the tuner If a channel is not active it is not modified See Tuning selected channels on page 18 5 3 Commands Menu This menu contains buttons for various commands that can be executed Reset channels Pressing this button causes resetting of all active channels See Resetting channels on page 13 Heat sensor Pressing this button heats the sensor element containing currently selected channel See Heating sensors on page 13 Heat all sensors Pressing this button heats all sensor units See Heating sensors on page 13 Sync electronics Synchronize Janitor state to electronics See Synchronizing Jani tor on page 59 Show all noise histories Selecting this button will show a graph containing noise histories of all channels superimposed on top of each other See Viewing noise history of a channel on page 17 Clear histories Clears the history records of all the channels See Viewing noise history of a channel on page 17 5 4 Search Menu This menu contains buttons that allows you to find channels according to some characteristic feature of the channel In order to make these searches to work the particular characteristic of the channel must be first mea sured Worst noise Next Ctri lt Key gt n Worst noise Search the
14. used 0 or 1 measurement IgnoreAfterReset integer How many buffers to ignore after reset measurement GoodEnough float Level below which the tuning is stopped Table B 3 Noise measurement parameters The FFT parameters describe how the spectral calculations are performed The parameters are listed in Table B 4 class parameter name type measurement TimeBufSize integer Time buffer length s measurement FFTsize integer Length ofthe FFT transforms samples measurement FFThpf float High pass filter used in FFT meas Hz 72 Table B 4 FFT measurement parameters NM21283A B Parameters B class parameter name type measurement FFTlpf float Low pass filter used in FFT meas Hz measurement FFTsfreq float Sampling frequency used in FFT meas Hz measurement FFTaverages integer Number of averages in spectra measurement FFTssp integer is SSP used in spectra calculation measurement FFTlowStart float Start of low frequency interval Hz measurement FFTlowEnd float End of the low frequency interval Hz measurement FFTwhiteStart float Start of the white noise interval Hz measurement FFTwhiteEnd float End of the white noise interval Hz Table B 4 FFT measurement parameters The tuning setting gives parameters that affect the offset value tuning The parameters are listed in Table B 5 clas
15. 0 31 Flux quantum 28 G Gate setting 53 voltage 29 32 Gradiometer 27 H Heating sensors 13 Help online 10 Histogram changing bin width 16 Histograms changing resolution 16 viewing noise level 16 Phi measurement 46 I V characteristics 28 I V curve 54 L Loading settings 14 56 Locking channels 19 Magnetometer 27 Main window 10 Manual tuning 33 35 Measurement modes 43 Measurement parameters 45 Measuring characteristics 53 derivative information 54 flux quantum size 54 gate curves 55 I Phi curves with Squiddler 34 I Phi curves with Tuner 34 I V curve 54 59 noise level 47 Noise level with Squiddler 34 signal samples 50 spectra 49 white noise level 11 17 Menu Command 22 File 21 Help 23 Parameters 21 45 Search 22 View 23 Menus using 5 Modulation depth explanation 28 79 EB INDEX N Noise cancellation of the electronics 29 Noise history 17 O Offset setting 53 voltage 32 Operating point 31 53 parameters of 53 reverting 57 P Parameter class 45 Parameter set 45 Parameters measurement 45 of FFT measurement 49 of I Phi measurement 46 of noise measurement 48 Point of operation See Operating point Power up settings 58 Preferences 21 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 level 43 Showing noise lev
16. 283A B 2 1 Getting started This chapter gives you an overview of the program explains how to start and stop it and provides some basic aspects that you need to know Beginning a session The tuner program can be started in three ways Selecting the Tuner button in the Tools menu of the acquisition pro gram Measurements using acquisition program should be stopped before starting the tuner See Data acquisition User s Manual for details of the acquisition program Using the graphical user interface of the operating system by double clicking the tuner icon in Maintenance toolbox under the MEG analysis toolbox Giving a suitable command in UNIX shell For the proper command and options refer to Appendix A Only one tuning program should be running at any time If the tuning pro gram is already running on the same system the new starting program shows an question dialog warning 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 instance of the program running for example if the program was killed or it died unexpectedly If you are sure that there is no other copy running you can go on using the program by responding with Can cel button After starting the program a user interface similar to Figure 2 1 appears On the top of the window is a menu bar that allo
17. D working principles see Principles of SQUID operation on page 27 and to basic Tuner operation see Basic Usage on page 3 The manual tuning can be done using two different programs and both are described here only as much as it is needed to per form the manual tuning Need for manual tuning NM21283A B When the system is cooled down for the first time a manual tuning must be performed for all channels The tuning settings are strictly valid only for a certain SQUID sensor electronics card pair Therefore if a SQUID sensor is changed or if an electronics card is changed new settings must be searched manually Note that each electronics card drives 12 SQUIDs if a card is changed all channels belonging to that card must be adjusted After major service operations e g warm up cool down cycle it is advisable to check the tuning settings by going through the manual 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 level see About saving and loading settings on page 14 If that does not help point of operation should be tuned manually 7 2 Tools for manual tuning Since Vectorview flux locked loop electronics are digital all tuning dis plays are computer generated and no physical tools are needed What is needed is a x y display to show the flux vs
18. Elekta Neuromag Sensor Tuner User s Guide Software Version 3 2 for Elekta Neuromag May 2009 ELEKTA NEUROSCIENCE This document contains copyrighted and possibly confidential information and is intended for the exclusive use of customers having Neuromag products and authorized representatives of Elekta Neuromag Oy Disclosure to others or other use is strictly prohibited without the express written authorization of Elekta Neuromag Oy Elekta Neuromag Oy reserves the right to make changes in the specifications or data shown herein at any time with out notice or obligation Elekta Neuromag Oy makes no warranty of any kind with regard to this document and the 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 direct indirect incidental or consequential damages in connection with the furnishing performance or use of this material and software Elekta Neuromag Vectorview and Neuromag System are trade marks of Elekta Neuromag Oy UNIX is a trademark of UNIX System Laboratories Inc and Motif is a trademark of Open Software Foundation Inc Editor Matti Kajola 2001 2009 Elekta Neuromag Oy All rights reserved Printed in Finland Printing History Neuromag p n Software Date lst edition NM21283A tune_vv 3 0 x 2001 12 27 2st edition NM21283A A tune_vv 3 0
19. R 6 6 1 Principles of SQUID operation This chapter explains the operating principles of a SQUID sensor and readout electronics It gives the necessary background information that is needed in manual tuning of the sensors Operation of a SQUID magnetometer NM21283A B The Superconducting QUantum Interference Device SQUID is the only sensor with sufficient sensitivity for biomagnetic measurements The SQUID is a transducer that converts magnetic flux into electric signal The basic structure of a SQUID magnetometer is illustrated in Figure 6 1 The external magnetic field is not sensed directly by the SQUID rather it is coupled to the SQUID detector by means of a flux transformer The flux transformer consists of two coils a pickup coil 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 times sensor area Vectorview uses two kinds of pickup loops magnetometers and gradiometers Magnetometer loops are simple rectangular loops Gradiometer loops comprise two rectangular coils side by side wound in opposite sense This arrangement is near sighted which greatly improves the rejection of environmental magnetic noise Flux transformer SQUID Figure 6 1 Schematic of a SQUID sensor The SQUID is formed out of a superconducting ring interrupted by two weak links or so called Jos
20. T key simultaneously By using the active channels dialog which can be popped up by selecting the menu button Parameters gt 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 labeled with the number part of the channel names When the check box is set tuning is allowed for this particular channel You can switch individual channels by clicking the box and then closing the dialog by pressing OK button 0211 0311 0411 0511 Y 0611 0711 0811 0911 1011 1111 1211 1311 1411 1511 1611 1711 1811 1911 2011 2111 2211 2311 2411 2511 Y 2611 0111 vj0112 vj0113 v 0121 v 0122 v 0123 0131 0133 0212 0312 v 0412 0512 0612 v 0712 0812 0912 1012 1112 RA 1212 1312 1412 EA 1512 1612 CARTA 1812 1912 2012 2112 2212 2312 v 2412 v 2512 Y 2612 v 0213 v 0221 v 0222 v 0223 v 0231 0233 0313 0321 v 0322 v 0323 v 0331 0333 0413 v 0421 v 0422 v 0423 v 0431 0433 0513 0521 v 0522 v 0523 v 0531 0533 0613 0621 v 0622 v 0623 v 0631 0633 0713 v 0721 v 0722 v 0723 v 0731 0733 v 0813 v 0821 v 0822 v 0823 Y 0913 v 0921 v 0922 v 0923 v 0931 v 0932 v 0933 0941 1013 1021 v 1022 v 1023 1031 1032 1033 v 1041 Y 1113
21. X window system are used as values of the color settings A complete list of these names can be found from file usr lib X11 rgb txt class parameter name type description preference TraceColor string Color used in curves preference BgTraceColor string Backgroung trace color preference TextColor string Text color preference HistogramColor string Histogram boundary color preference LowFreqColor string Low frequency histogram fill color preference BandColor string White noise color for gradiometers preference BandColor2 string White noise color for magnetometers preference AliasedColor string Aliased noise color for histograms preference LockedColor string Histogram color for locked channels preference IgnoredColor string Histogram color for ignored channels preference ReadyColor string Histogram color for ready channels preference CursorColor string Cursor color preference NoiseNBins integer How many bins in noise histograms preference NoiseBinWidth float Bin width in noise histograms preference DCNBins integer How many bins in DC level histograms preference DCBinWidth float Bin width in DC level histograms preference LineNBins integer How many bins in line frequency histo grams preference LineBinWidth float Bin width in line frequency histograms preference expertLevel integer Current expert level Table B 10 Preferences NM21283A B 75 B Parameters Scaling parameters are used to preserve the display scales from o
22. a text field select first the text to be altered by pressing the mouse button 1 on the starting point of the text to be replaced and dragging the cursor to the end point of the text to be selected and then releasing the button The selected text should now have different background color that rest of the text Then simply type in the new text When you press the first character of the new text the old selected text will disappear Some text can be removed from a text field by first selecting it as described above and then pressing delete key Note that the last selected piece of text is also copied into the clipboard of the program The current selection in the clipboard can be pasted in any text field by clicking the insertion 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 long numbers is usually also more reliable that entering them manually 1 3 Using file selection boxes In several phases of the analysis one must select a file to be loaded or pro cessed In most cases user can do this selection using a file selection box dialog The figure on the left shows an example dialog On the top there is a field that contains a directory specification along with a file mask This specification defines the directory from which a file can be selected and the subset of files within this direct
23. ands that can be executed Reset channels 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 page 13 Heat all sensors Heat all sensors See Heating sensors on page 13 Sync electronics Synchronize Janitor state to electronics See Synchronizing Jani tor on page 59 Snapshot Mark current state as the nominal operating point See Operating point parameters on page 53 Estimate phi0 Estimate flux quantum sizes from a I Phi measurement results See Operating point parameters on page 53 Set biases to maxima Level 2 only Set bias value for each channel to achieve maximum modulation as determined from a bias scan Set gates to minima Level 2 only Set gate values to achieve minimum noise as determined from a gate scan Fractions to 1 3 Level 2 only Set offset value target point to 1 3 level of the modulation range Set dVdO to Level 2 only Manually set the offset adjustment unit to voltage scaling Show all noise histories Selecting this button will show the a graph containing noise histo ries of all channels superimposed on top of each other See View ing noise history of a channel on page 17 Clear histories Clears the history records of all the channels See Viewing noise history of a channel on page 17 NM21283A B 65 12 Description of full menus To
24. assifica tion schemes parameter sets and classes The parameter set defines which parameter dialog is used to edit them and the class defines the general context in which the parameter is used Typical sets are e g Noise mea surements and Tuning settings containing the parameters affecting the noise measurements and fine tuning Typical classes are e g Measure ment parameters and State parameters giving instructions to measure ment routines and describing operating point settings To change a parameter value 1 Select the button corresponding the parameter set of the parameter in the Parameters menu 2 Edit the value in the text box by the parameter name and press RETURN 3 Close the parameter box Closing the box is not necessary since the values are changed immediately when RETURN is pressed 45 H Basic measurements 46 8 4 View modes In most cases the result of a measurement can be displayed in several for mats or different aspects of the result can be shown For each measure ment job there are two principal displays One showing all channels and another showing one specific channel Typically the data shown for all sensors are somehow compressed To select the overview all channels set the active channel to 0 To show some particular channel select the channel either by clicking the bar rep resenting it or by using the operating point controls See Noise display on page 15
25. asurement system It facilitates the tun ing and monitoring of the performance of the sensor electronics The key features provided by the program are Measuring white noise level Automatic fine tuning of the noise level Adjusting sensor operating point manually Measuring several characteristic curves of the sensors Manual heating of single or all sensors The functionality of the program depends on the expert 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 affecting the program Using the fea tures in level 1 requires understanding of the operation of the sensor sys tem and is intended to be used by service personnel This manual is divided in three parts The first one describes how to tune the system automatically using the SQUID tuning program This is a everyday operation and reading of this part is recommended for all users All expert level 0 operations are explained The second part explains the operating principles of a SQUID sensor and electronics It also contains a detailed description how the sensors are tuned manually This information is essential for the maintenance person nel and for understanding advanced features of the tuning program The third part describes advanced features of the tuning program These are available when the expert level is set to 1 an
26. b If the bias voltage is further increased to V 5 the modulation depth decreases finally tending to zero At large bias voltages the SQUID looks like a resistor 6 2 SQUID electronics of Vectorview Figure 6 4 illustrates the principle of operation of the Vectorview readout electronics The signal is coupled from pickup coil to the SQUID via flux transformer as discussed in previous section In addition there is an aux iliary coil a so called feedback coil which is used by the readout electron ics to couple various 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 across its input terminals constant by feeding cur rent via the feedback resistor back to the input As a result the voltage over the SQUID remains at a preset value of V 5 and the current through the feedback resistor which is directly proportional to the operational amplifier output voltage then is the actual output signal Even with the best operational amplifiers the noise of the amplifier exceeds that of the SQUID Therefore Vectorview employs a so called amplifier noise cancellation circuit The basic idea is to couple the SQUID voltage through a variable conductance here a field effect transistor FET and an auxiliary coil back to the SQUID magnetically This posi tive feedback decreases the effect of the preamplifier volta
27. change the y scale of the display use the control buttons in the lower right corner of the display The buttons available are following Make bars look bigger Make bars look smaller e u Autoscale bars heights Give y scale numerically e Table 3 1 Note that the autoscale button is a toggle button If you press it once all following plots will be automatically scale and the scale varies from plot to plot To fix the scale again press the button an another time The autoscaling is also set off automatically if you press any other scaling but ton To enter a numeric value to the scale press the fourth button The whole area will change to a text box where you can enter the scale you want to use Pressing RETURN activates the new value and the icons are shown again If you see a bar indicating a noisy channel and you want to know which channel that is move cursor over the bar and press the left button The name and noise level at that channel is shown in the information area See Figure 2 1 on page 10 15 H Basic tuning operations It is also possible to show the noise values as a histogram To do that select View Noise histogram from the menus In the bar histogram gra 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 one so no bars are hidden behi
28. channel with largest white noise 22 NM21283A B Description of the menus H Next Search next channel This button performs an incremental search using the same criterion as the last search to find second third etc bad channel 5 5 View Menu This menu contains buttons that select what information is shown in the graphics area This setting is also changed 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 noise levels to be shown as a histogram 5 6 Help Menu The help menu contains currently only one button that displays the ver sion and the linking time of the program NM21283A B 23 H Description of the menus 24 NM21283A B PART 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 NM21283A B 25 26 NM21283A B Principles of SQUID operation n CHAPTE
29. cs of Vectorview 29 6 3 Optimal point of operation 31 Chapter 7 Manual tuning 33 7 1 Need for manual tuning LL 33 7 2 Tools for manual tuning nenn 33 7 3 Measuring flux to current curves using Squiddler 34 7 4 Measuring flux to current curves using Tuner 34 7 5 Measuring noise level nennen 34 7 6 Manual tuning procedure LL 35 7 7 Typical sensor problems 39 Part 3 Advanced features Chapter 8 Basic measurements 43 8 1 Setting the expert level nen 43 8 2 Selecting and running jobs 44 8 3 Measurement parameters Lus 45 8 4 VIEW Mod s ironia iii cse 46 8 5 I Phi measurement elles 46 8 6 Noise measurement creen 47 8 7 FFT measurement nennen nenn 49 8 8 Signal 4 x oos ood ee TR Re 50 Chapter 9 Tuning procedures 51 9 1 Noise level based tuning 51 9 2 Tuning based on characteristics 52 9 3 Manual tuning 26 64 omo LESE EE DE aa 52 Chapter 10 Measuring characteristics 53 10 1 Operating point parameters 53 10 2 Measuring derivative information 54 10 3 Measuring and using current voltage characteristic
30. ctral noise density per unit band 1 Hz The length of the time buffer should be at least the length of the Fourier transform In order to get better statistics several spectra can be averaged The number of averages is controlled 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 parameters in Table 8 3 define two bands one for numerical estimation of the low frequency noise and another for estimating the white noise level The noise power in these bands can be shown as a bar dia gram NM21283A B 49 H Basic measurements The FFT measurement results can be displayed using following view modes FFT This mode shows the sensor environment noise level Overview shows three sets of bars superposed on top of each other Bars from front to back aliasing noise level white white noise level red and low frequency noise level black All noises are displayed in RMS per Hz Single channel view shows the RMS spectrum of the selected channel 8 8 Signal This job measures a sample of time signal trace The length of the trace is controlled by the parameter TimeBufSize in parameter set FFT measure ments When this job is selected the single channel view shows the time trace of that particular channel The overview mode shows the last FFT measurement result if any 50 NM21283A B Tuning proc
31. current I characteristics a display to show real time signal or noise level and controls to alter the bias offset and gate settings of a SQUID There are two tools for manual tuning You can either use the SQUID tuning program in expert level 1 or Squiddler which is a small controller dialog accessing the electronics set tings directly The SQUID tuning program provides more auxiliary func tionality to ease the tuning but the Squiddler works faster has better response times since it does not make any measurements Squiddler is used in conjunction with the normal acquisition program to make the required measurements The tuning program is used for both measuring and adjusting 33 E Manual tuning 34 7 3 Measuring flux to current curves using Squiddler The I curves of a SQUID sensor can be measured using Squiddler and acquisition program For the meaning of I curve see Operation of a SQUID magnetometer on page 27 To measure I Phi curves using Squiddler 1 Start both acquisition program and the Squiddler program See Data Acquisition User s manual 2 Press the x y button at the lower part of the raw data display to show the x y display 3 Start acquisition Default parameters are fine 4 Set the measurement mode to tuning mode by selecting Mode Tune from the Squiddler menu 5 Select the channel to be viewed using Squiddler You can either enter the name of the channel into the text field Chan
32. d are normally used only by the maintenance personnel NM21283A B PART 1 Basic Usage This part describes the basic usage of 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 Reading of this part is recommended for all users of a Vectorview system NM21283A B NM21283A B CHAPTER 1 1 1 User interface basics This chapter explains the notation conventions used in this manual and the basics of the user interface manipulation If you are familiar with the Motif interface you may want to skip the rest of this chapter The descrip tion of the interface given here is not intended to be complete but rather to give enough of information to let a novice user to operate the program For more information about the general manipulation of the operating sys tem interface refer to User s Guide of Common Desktop Environment Using menus NM21283A B 1 2 On the top of the main window of the program lies a horizontal bar con taining so called menus Each one is represented by its name When the name is clicked with the mouse button 1 usually the leftmost button a stack of buttons appears This stack of buttons is called a menu You can initiate different kinds of operations by clicking corresponding button in a menu When a button within the menu is pressed and the mouse bu
33. d the derivative information should be measured See Measuring derivative information on page 54 The file can be saved normally using the File gt Save settings menu command The third file loaded is deduced from the current helium level and is assumed to contain the nominal operating point settings Only the operat ing point settings are loaded However these settings are not activated automatically so that the current operating point is not changed If the nominal and current operating point do differ one can get to the nominal one either by reloading the file explicitly or by File gt Revert to previous op menu command This file should be saved after tuning the system See About saving and loading settings on page 14 Note Loading of the operating point parameters works differently during the initial loading and when the parameters are loaded explicitly 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 loaded explicitly the new values are sent also to the magnetometer The last file loaded is the preferences file which contains the personal preferences settings for each user Only the parameters in class prefer ences are loaded The preferences are saved automatically each time the program is exited 11 6 Updating the power up settings The power up settings contain th
34. e sensor tuning parameters that are auto matically loaded after a power cycle completes These have been initially set at the factory to values that should enable reasonable operation of the system Normally these values should not be changed unless there is a major service operation which results in a substantial change of the tun ing To update the power up settings file 1 Using a Unix shell connect first to the Janitor program at the real time computer assuming that the server runs on computer called kaptahl telnet kaptahl janitor 2 Enter the password pass lt password gt 3 Issue a dump command dump current take note of the response observing that the command succeeded Now issue command quit 4 Make a backup copy of a file neuro dacg setup janitor powerup on the workstation Copy the newly created power up file from tmp jan NM21283A B Miscellaneous ul 11 7 itor dump located on the real time computer to neuro dacg setup janitorpowerup on the workstation as follows enter telnet kaptahl Enter user name root no password Then issue com mand cp tmp janitor dump neuro dacqg setup janitor powerup Then exit the telnet terminal Synchronizing Janitor NM21283A B 11 8 If the pre amplifier power is brought down the registers on the boards lose their contents Currently this situation is not automatically noticed by the Janitor electronics software driver running at the real ti
35. e tuning on page 12 or tune the noise level manually using the following instructions Adjust the gate voltage by the arrow keys step by steps on both sides Observe the noise amplitude and see whether it can be made smaller by adjusting the gate If you are uncertain about the 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 e Finally try adjusting the offset a few steps on both sides to see whether the noise can be made smaller If there is no clear change leave the setting at its original value If the signal shows extra white noise evenly distributed the gate probably needs adjustment if the signal shows spikes especially 38 NM21283A B Manual tuning Ed NM21283A B with an unsymmetrical distribution probably the offset needs read justment 7 If the noise level is still higher than in other channels check the current vs flux characteristics again and try readjusting the bias step 3 7 7 Typical sensor problems This section describes several types of sensor problems and the proce dures how to deal with them Tuning the sensors in presence of strong disturbances may cause the noise level measurements to be affected by them This appears as abnor mally high average noise level on magnetometer channels This external noise masks the sensor noise and makes the tuning difficul
36. ed by typing in a number followed by a return or by changing the setting one by one using the right arrow and left arrow keys If the system has been tuned earlier start from the current bias and offset values Otherwise set the offset voltage to a value near the middle 128 Adjust the bias until you find the point where the lower end of the current vs flux characteristics curve shows a pla teau like curve Vp of Figure 7 1 a Start the bias search from about 150 and decrease the value using the left arrow key until you 35 E Manual tuning 36 A see the plateau If you go down too much the current vs flux char acteristics goes via zero and turns over see Fig Figure 7 1 b Be sure to be on the right side Dm RE B1 Figure 7 1 Bias tuning Adjust the offset voltage so that the current vs flux characteristics is approximately in the middle of the screen From the point where the plateau on the bottom appears increase the bias setting until it has completely disappeared see curve Vp You may decrease the bias further by one or two units to ensure sta bility The current vs flux characteristics should look rather smooth now If the current vs flux characteristics is not smooth set the gate volt age to 150 If this does not remove irregularities try increasing the bias setting even with the expense of loosing some modulation depth Adjust the gate voltage NM21283A B Manual t
37. ed in more detail in the following sections The jobs available are I Phi Measure flux vs current curves Noise Measure white noise levels FFT Measure spectra Signal Measure signal trace Tune Tune noise Tune fine Fine tune noise Tune gate Tune noise adjusting only gate values Tune offs Tune offset setting Manual tune Measure I Phi curves fast to allow manual tuning Meas derivatives Measure parameter derivatives at operating point To run a measurement select it from the Job menu unless it is 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 button There are two kinds of jobs Some of them are continuous they continue until they are explicitly stopped Others are one time jobs which are started and they automatically stop when they are ready The acquisition system runs in three different states during the usage of Tuner It can be either idle suspended or active When the program starts the acquisition is idle unless somebody else is performing a measure ment When a job is initiated the acquisition system is started and it becomes active When a job stops the acquisition is suspended not stopped This means that the front end Collector program is actually col lecting data continuously but it is not sent to the clients like Tun
38. ed posi tion thus this phenomenon is often called flux trapping The flux trapping in the sensor coils is not problematic if the flux really stays in place Unfortunately it is quite common that the trapped flux moves between e g two points Since the flux pinned into the film 1s always strong even a very small movement cause severe jumping in the sensor signal If the flux trapping occurs so that the flux penetrates the Josephson junc tions in the SQUID the sensor ceases to work If the pinning point is in near neighborhood of the junctions the extra field leaking through the junctions cause the modulation depth of the SQUID to diminish This can manifest itself as increased noise or if the effect is reasonably small as moving of the optimal operating point bias offset and gate voltages to somewhat different values The magnetic flux in the thin films of the sensor can be removed by heat ing the sensor above the critical temperature of the films and then letting it cool down again The sensors in Vectorview are equipped with small 13 H Basic tuning operations 14 hearing resistors so that this can be easily achieved by feeding a suitable current pulse into the resistor Note that each sensor unit contains three SQUIDs so three channels are always heated together To heat a single sensor that contains a particular channel 1 Select the view channel by entering the channel name to the selection box of the workin
39. edures g CHAPTER 9 NM21283A B 9 1 Tuning procedures The tuning program is capable to perform several automatic tuning opera tions in addition to manual tuning This chapter describes the tuning oper ations available All the tuning operations are based on the measurements described in the previous chapter They typically employ a loop containing a measurement and adjusting of some parameters The tuning procedures available are the following Tune Optimize the white noise level by adjusting bias offset and gate settings Tune fine Same as Tune but with smaller steps in adjustments Tune gate Same as Tune but only the gate value is adjusted Tune offs Adjusts the offset setting so that the zero line in the I plot crosses the curve at specified level 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 They differ only on adjusted parameters and the size of the adjust ment steps The basic job Tune is provided for general purpose everyday tuning A detailed description of its usage is given in part Basic Usage starting on page 3 It measures the white noise level adjusts one parameter and then measures again If the new noise level was lower than the previous the new settings are accepted The sequence of adjustment is such that the gate value is opt
40. el as histogram 16 Snapshot 53 SQUID operation 27 SSP and sensor problems 39 how to use 59 80 Start button 9 Starting measurement 44 program 9 Starting program 9 Start up files 57 Status area 10 Stop button 9 Stopping program 10 T Text fields using 5 Troubleshooting 17 Tuning manually 35 52 offset level 52 procedures 51 selected channels 18 white noise level 12 51 V View modes 46 W Workspace 10 oo List of procedures To change a parameter value 45 To change back to view all channels 18 To change the expert level setting 43 To heat a single sensor that contains a particular channel 14 To heat all the sensors 14 To load tuning settings into tuner and magnetometer 14 To measure I Phi curves using Squiddler 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 To measure white noise levels using Tuner 11 To reset all channels 13 To revert settings to state at program start up time 57 To revert to the previous nominal point of operation 57 To save tuning settings into a file 15 To tune a sensor manually 35 To tune sensors automatically 12 To update the power up settings file 58 NM21283A 81 ELEKTA NEUROSCIENCE Elekta Neuromag Oy Siltasaarenkatu 18 20 FI 00530 Helsinki Finland Tel 358 9 756 2400 Fax 358 9 756
41. ent vs flux characteristics is also affected by the gate voltage setting When in doubt always set the gate voltage to value 150 to decouple the amplifier noise cancellation before trying to find a bias setting at which the current vs flux characteristics looks smooth Warning Do not adjust gate setting to values below 150 unless the opti mum noise is achieved with a lower value Some FET transistors may alter their characteristics with low bias voltages This manifests as a shift in the optimal gate setting which relaxes in a couple of hours 31 n Principles of SQUID operation The offset should be set so that the current vs flux characteristics curve crosses zero in order to be able to operate the flux locked loop The actual point of operation to which the system locks is determined by the point 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 achieved for an offset setting where the zero level crosses the current vs flux char acteristics one quarter above the minimum of the curve The gate voltage setting affects the amount of amplifier noise cancella tion It is set to a value where the noise is at minimum 32 NM21283A B Manual tuning KA CHAPTER 7 7 1 Manual tuning This chapter deals with the manual tuning procedure We assume here that the user is familiar to SQUI
42. ephson junctions Without these interruptions the external magnetic fields such as those generated by the brain would have no detectable effect on the superconducting ring These links consist of a microscopical isolating layer that is thin enough to ensure that the 27 n Principles of SQUID operation 28 ring will maintain its superconducting properties but only up to a certain limit When operating the SQUID a small current bias current is fed through the SQUID ring and the voltage over the device is measured When the current through the SQUID is small no voltage appears because the ring is totally superconducting Above a critical value critical current a volt age drop appears The apparent critical current of the SQUID depends on the magnetic flux threading the ring Thus maintaining the bias current at a suitable level a small change in the magnetic flux coupled from the external source via the flux transformer will change the point where the ring loses its superconductivity and voltage drop appears This results in a modulation of the voltage as a function of magnetic field Figure 6 2 Current voltage characteristics of a SQUID Another way is to fix the voltage 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 of a typical SQUID sensor The characteristics co
43. er The benefit of this arrangement is that if the measurement parameters are not changed a new measurement can be started without delays The stop but ton has a dual action When a measurement is running pressing it stops the current operation and suspends the acquisition The label on the stop NM21283A B Basic measurements g NM21283A B 8 3 button is changed to Stop collector Another press will then stop the acquisition and release the acquisition front end The measurement system must be idle to start new measurements using the normal acquisition program It is not necessary but recommend to exit the Tuner in order to use acquisition but the measurement must be stopped into idle mode Measurement parameters Each measurement or job has a set of parameters associated to it These affect the exact details how some operation is performed Typical exam ples are sampling frequencies and number of averages taken The default values are adjusted to be good for normal usage but some times it is use ful to be able to adjust them In addition to measurement parameters pro gram uses also various other parameters for defining operating points preferences etc The 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 through the Parameters menu They are classified using two cl
44. es of a SQUID sensor These measurements are based on the basic measurements described in Chapter 8 Typically a curve is measured by repeating a mea surement with different parameter settings and picking up some particular aspects of the measurement result Measuring the I curve is regarded as a basic measurements and is described in I Phi measurement on page 46 Operating point parameters The operating point of a SQUID is defined by the bias offset and gate settings as described in Chapter 6 In addition to these settings the char acteristics of the SQUID at some particular operating point can be described by a set of parameters like modulation depth etc Some of these parameters are needed by the tuning routines some are useful in checking the proper operation of the sensor The program has two concepts for the operating point 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 state file or the state which prevailed when a state file was saved which ever has occurred last The current state can be set as the nominal operating point also by selecting Commands gt Snapshot from the menus One can examine the estimated parameters of each channel using Chan nel info dialog available through View Channel info menu button For each parameter two values are shown one
45. g point controls at the left side of the display area Press return and check that the name of the channel appear on the top of the display 2 Select Command gt Heat sensor from the menus To heat all the sensors 1 Select Command gt Heat all sensors from the menus If you are making a noise measurement you need also reset the electron ics after heating See Resetting channels on page 13 3 5 About saving and loading settings Tuning settings can be saved on disk and loaded back to magnetometer later on Recommended practice is that there should be two or three stan dard settings files that contain carefully made good values for normal usage and some special 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 system does not succeed one should try first to heat bad channels and if that is not enough load a well known tun ing setting file If this tuning still fails contact your system administrator to find out what has changed It is not recommended that the tuning settings are saved after each fine tuning and then reloaded when tuning is needed next time since then the tuning settings files tend to drift and nobody really knows how the sys tem should perform when some particular file is used It is usually better to have fixed files that are saved only by the administrative
46. ge 56 Load gt Load selected params Load some selected parameter sets to all channels See Loading and saving in special cases on page 56 Load gt Load I V curve Level 2 only Load current operating point I V curves from a file Load gt Load gate curve Level 2 only Load current operating point gate curves from a file Load gt Load I V on meas Level 2 only Replace existing measured I V curves from a file Load gt Load gate on meas Level 2 only Replace existing measured gate curves from a file Save gt Save selected params Save some selected parameter groups only See Loading and sav ing in special cases on page 56 Save gt Save noise in ASCII Level 2 only Save selectable noise values into a text file Save gt Save I V curve Level 2 only Save the measured scanned I V curves Save gt Save gate curve Level 2 only Save the measured scanned gate curves Print gt Print all I V curves Level 2 only Print all I V curves Preferences This button opens a dialog box that can be used to set preference information like some colors and the expert level Preference infor mation is always saved when program exits For description of the preference parameters see Appendix B Exit Use this button to stop the program A verification is required to really stop the program See Ending a session on page 10 NM21283A B Description of full menus 12 NM21283A
47. ge noise By adjusting the gate voltage of the FET the strength of this coupling can be 29 30 Principles of SQUID operation Amplifier Amplifier Integrator Loop switch coil Fal e BA Feedback coil Vexcitation SQUID Analog part Digital part Figure 6 4 SQUID electronics adjusted with large negative gate voltage the conductivity 1s low and the effect of the amplifier noise cancellation circuit remains small When the gate voltage is made less negative the compensating effect increases and finally cancels the amplifier noise If the gate voltage is further increased the feedback coupling becomes too large leading to instability and increased noise Since the current vs flux characteristics are periodic with respect to flux the sign of the derivative 0V 0 may be either positive or negative Therefore the amplifier noise cancellation circuit only works where the derivative has a proper sign say on the falling slope The actual sign of the slope where amplifier noise cancellation is effective depends on how the feedback coil is arranged On the opposite slope the noise is increased rather than decreased The proper tuning of the gate voltage is discussed in more detail in 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 feedback loop switch see F
48. ggle broken status Toggle status flag used for marking broken channels See Marking broken channels on page 57 12 5 Search Menu This menu contains buttons that allows you to find channels according to some characteristic feature of the channel In order to make these searches to work the particular characteristic of the channel must be first mea sured See Searching channels on page 56 Worst offset Find channel with largest error in 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 performs an incremental search using the same criterion as the last search activated by one of the buttons described above to find second third etc bad channel 12 6 View Menu This menu contains buttons that select the information shown on the graphics area This setting is also changed to a default value when a job is selected from the Job menu so it is not often needed Channel info This button pops up a dialog box that shows miscellaneous informa tion about the current settings of the selected channel See Operat ing point parameters on page 53 Raw trace Show the I Phi data time trace I Phi curve Select the I Phi curve to be shown on the graphics area Curve is shown only if a I Phi measurement has been performed during the session See I Phi measureme
49. good channels 39 Ed Manual tuning 40 NM21283A B PART 3 Advanced features This part describes the advanced features of the SQUID tuning pro gram These include measuring various characteristics of the sensors and manual and 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 everyday use see Part 1 The basic knowledge on SQUID operating principles and Vectorview electronics given in Part 2 is assumed For a general description of manual tuning refer to Part 2 NM21283A B 41 42 NM21283A B Basic measurements g CHAPTER 8 8 1 Basic measurements The tuning program is a versatile tool that can be used measure several characteristics of a SQUID sensor These measurements are used with suitable adjustment routines to perform various optimization and charac terization operations This chapter describes the basic measurements that can be made The basic measurements available are the following I Phi Measure flux to current transfer function of the SQUIDs This mea surement is used to view the SQUID characteristics to measure modulation depths for detecting flux trapped sensors and to mea sure I V curves of the SQUIDs Noise Measure the white noise level of the sensors This provides a fast measurement of the white noise levels Also the dc and line fre
50. he door of the shielded room is closed If the noise still looks very high or some channels are saturated small black bars appear in the display try heating the noisy channels See Heating sensors on page 13 If the over all noise level is very high you probably need to load suitable tuning set tings from a file before doing the fine tuning See About 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 auto tuning routine of the tuning program should be able to fine tune the noise levels to normal To tune sensors automatically 1 Start a noise level measurement 2 Press the start button again the same button that was used to start the noise measurement The button should now have text Tune on it 3 Wait until the tuning has obtained good noise values Or hopefully not failed to tune the noise The tuning does not stop automatically It continues until it is explicitly stopped 4 Press Stop tuning button 5 Press Stop collector button the same stop button as before which now has different text on it to release the acquisition system for normal measurements Warning All measurements should be made with the doors of the shielded room closed Warning Heat single noisy channels before tuning Tuning may success even with flux trapped SQUID but then the tuning is
51. he menus 4 Press the start button and wait until the measurement is finished This measurement calculates also estimates 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 in many cases the operating point does not matter as long as the signals do not saturate during the measurement 10 3 Measuring and using current voltage characteristics To measure the I V curve of the SQUIDs 1 Check that derivative information is available If not measure it See Section 10 2 2 Select Job gt I V curve from the menus 3 Press the start button and wait until the measurement stops The I V curves are displayed using three curves two showing the extre mum values and one showing the modulation depth A cursor cross hair shows the current operating point in the graph The curves are available until the end of the session One usage for the I V curves is a quick initial tuning When the I V curves have been measured one can set the operating point of the SQUID by clicking a point in the graph with the left mouse button having both SHIFT and CTRL buttons pressed NM21283A B Measuring characteristics E 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 un
52. igure 6 4 is closed a current proportional to the time integral of the SQUID output voltage is fed to the feedback coil As a result the point of operation along the current vs flux characteristics changes and the corresponding current through the SQUID changes A stable point is only reached if the input of the integrating amplifier reaches zero Therefore an offset is added to the current vs flux characteristics to make the curve pass through zero line The system then locks to the point of operation where the apparent out put of the SQUID containing the additional offset is zero any change in the input flux from the gradiometer causes a change in the feedback cur rent that exactly compensates the input flux change Thus the feedback NM21283A B Principles of SQUID operation n current is a replica of the input flux Since the SQUID with its periodic response is now operated as a null detector the final output signal a volt age directly proportional to the feedback current is linear For tuning purposes it is necessary to feed in external flux to see the cur rent vs flux characteristics Therefore an external flux signal can be fed through the feedback coil In Vectorview the flux locked loop is implemented using digital signal processors which allow accurate operation and plenty of flexibility All loop characteristics operating modes and filters are digital and easy to control Signal processors reside physically in
53. imized first starting with rather large steps that then shorten quite quickly After the initial rounds on gate the routine enters into a loop optimizing sequentially bias offset and gate values with a step size of 2 The Tune fine works similarly optimizing all parameters using step of one unit 51 BH Tuning procedures The Tune gate mode adjusts only gate values Bias and offset values are left intact 9 2 Tuning based on characteristics 52 The tuning mode Tune offs differs considerably from the tuning modes described in the previous section Instead of measuring the noise level it measures the I curve and adjusts the offset so that the curve meets an predefined 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 offset settings are changed 9 3 Manual tuning To perform manual tuning the tuning program provides a special mea surement mode Manual tune This is optimized for manual operation so that the measurement speed and update frequency are maximized No adjustments are made automatically You can alter the settings using the controls in the upper left corner of the user interface NM21283A B Measuring characteristics E cHAPTER 10 Measuring characteristics NM21283A B 10 1 This chapter describes how to measure several characteristic curv
54. ing point tuning values by 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 failed and the noise has been lower with some other parameters than the current ones You can read the old parameters by clicking the noise history curve at the point where the noise was low and then write the tuning values into the operating point control area at the left top corner This way you can easily get back the good values Another typical usage for reading old tuning values is to check that some abrupt change in noise is not due to change in tuning values but because of a change in the sensor or environment The Command menu contains buttons that can be used to show noise his tories of all channels at the same time and to clear the history records 4 3 Tuning selected channels In some cases it may be useful to tune only some selected channels This is possible by locking some channels When channels are locked they are ignored in all automatic tuning operations Locked channels are shown as black bars in the noise displays and their noise values are not taken into account when the average value shown on top of the display is calculated NM21283A B Troubleshooting E Channels can be locked by two methods by clicking the noise bar in the display using the left mouse button while pressing the SHIF
55. ings system HistoryDir string Directory for history files system ReferenceIV string Reference I V system NoiseLog string Noise log file name system AuxCollVar string Auxiliary collector variable to be sent system ReferenceCh integer X signal name NM21283A B Table B 1 System Parameters 71 B Parameters The I Phi parameters contain parameters that are related to I Phi measure ments The parameters are shown in Table B 2 class parameter name type description measurement AveLength integer Number of x bins in x y trace curves measurement NumAverages integer Number of averages in I Phi measure ments measurement TuneSfreq float Sampling frequency used in I Phi mea surements Hz measurement FuncAmp float Function generator amplitude V measurement FuncFreq float Function generator frequency Hz measurement WuFulnterval integer reserved Table B 2 I Phi measurement parameters The noise measurement parameters describe how to make a white noise measurement The parameters are described in Table B 3 class parameter name type description measurement NoiseHpf float High pass filter used Hz measurement NoiseLpf float Low pass filter to be used Hz measurement NoiseSfreq float Sampling frequency to be used Hz measurement NoiseNAve integer Number of averages taken measurement NoiseSsp integer Is SSP
56. l button to deactivate all channels and then activate the channel you want to tune by clicking its activation button NM21283A B CHAPTER 5 5 1 Description of the menus This chapter contains descriptions of the menus as they appear in lowest expert level For full menu descriptions see Description of full menus on page 61 File Menu The File menu contains commands that are related to saving and loading of the internal state of the program and the measurement device Load tunings This button enables you to load magnetometer state from a file The file must be in the tuner parameter format tnp Using this com mand only the state parameters are loaded all the rest 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 operating point information within the program to values being used at the saving time See also About saving and loading settings on page 14 Preferences This button opens a dialog box that can be used to set preference information like some colors and the expert level Preference infor mation is always saved when program exits Exit Use this button to stop the program A verification is required to really stop the program 5 2 Parameters Menu NM21283A B This menu contains buttons that pop up dialogs that enable the modifica
57. ld parameter files They are not used by the program class parameter name type description obsolete VErrorNBins integer obsolete obsolete VErrorBinWidth float obsolete obsolete MarkerStyle integer obsolete obsolete TuneBand float obsolete obsolete Npoles integer obsolete obsolete Step integer obsolete obsolete SpectrumLen integer obsolete Table B 14 Obsolete parameters NM21283A B 77 B Revision history APPENDIX c Revision history This appendix describes changes made both to the manual and the pro gram This manual applies to program tune vv version 3 2 x which 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 reasons the first release of tune vv is numbered 3 0 rather than 1 0 This is the third edition of the manual The differences from the second edition are a the company logo has been updated and b Command menu labels have been updated 78 NM21283A B INDEX ER Index A Acquisition modes 44 B Beginning a session 9 Bias current 28 setting 53 voltage 28 29 Broken channels 57 C Channel info 53 Controlling displays 15 E Electronics description 29 Exiting program 10 Expert level 1 setting of 43 F FFT measurements 49 File selection box using 6 Flux locked loop 3
58. lue settings 67 12 Description of full menus Gate history Show history of gate value settings 12 7 Help Menu The help menu contains only one button that displays the version and the linking time of the program 68 NM21283A B Description of full menus 12 NM21283A B 69 A Command line options APPENDIX A 70 Command line options This appendix describes the command line arguments and options of the tuning program Command syntax tune_vv lt options gt Command line options nolock Ignore lock files expert lt number gt Set the expert level of the user default lt measurement gt Set the default measurement mode The valid values for the mea surements with this option are tune fine tune noise i phi manual tune fft gate bias offs modu signal defs lt filename gt Define the name of the file containing the system parameters default values static lt filename gt Define the name of the file containing the static parameters load lt filename gt Define the name of the state file to load in start up site lt filename gt Define the name string describing the measurement site device lt filename gt Define the name string describing the device The valid values for the measurements with the default option are tune fine tune noise i phi manual tune fft gate bias offs modu signal NM21283A B Parameters B APPENDIX B Parameters This a
59. me comput ers Janitor can be forced to update all values in the electronics by giving a sync command This can be easily achieved by selecting the Com mands Sync electronics command from the menus In normal situa tion this command just refreshes all registers in the dewar top electronics so it should not cause any harm to issue the command Using SSP Noise reduction based on signal space projection SSP can be used in several measurement mode Modes that allow the noise reduction have a parameter xxxSSP where xxx depends on the measurement The need of using the noise reduction depends on case to case The normal tuning can be performed without SSP unless the environment is very noisy On the other hand spectra calculated for the magnetometers are severely affected by the external noise unless SSP is used 59 ul Miscellaneous 60 NM21283A B cHAPTER 12 Description of full menus 12 1 This chapter lists reference information about all menu functions There is only a brief description of the actions here and possibly a reference to a more detailed description The availability of the menu functions depends on the chosen expert level setting Menu entries described below are avail able on expert level 1 recommended experienced user level unless indi cated to be available only on expert level 2 recommended only for very special needs File Menu NM21283A B The file menu contains commands that are related
60. n program can not perform measurements if the tuner is accessing the measurement system To enable measurements press stop button to stop current operation and then another time to release the collector software part responsible for delivering the magne tometer data It is recommended that you then exit the tuning program even though that is not necessary to perform normal acquisition The program now starts measuring the noise level of the system The noise level of all channels is shown on a bar display in the display area Normally all bars should be red and display value between 2 to 5 fT Hz fT cm Hz for gradiometers Small negative bars indicate channels that are saturated and probably are not operating in flux locked mode not functioning properly Note that the colors can be adjusted personally The above description refers to default colors 11 H Basic tuning operations 12 If the noise values look good you can press the stop button exit the pro gram and go on measuring with the acquisition program If not proceed to tune the channels This is explained in the next section 3 2 Fine tuning Normally the program is used to tune slight offsets from a good operating point that is set after the installation of the system or thermal cycling This is referred as fine tuning Before tuning one should measure the noise level See Measuring the sensor noise level on page 11 If it is abnormally high check that t
61. nd the others Histogram bin width and number of bins can be adjusted from the prefer ences dialog box See Appendix B for meanings of the parameters 16 NM21283A B CHAPTER 4 4 1 Troubleshooting This chapter describes how to deal with the most common problems with the sensors For a more detailed description of the manual tuning and trouble shooting see Manual tuning on page 33 Also some more advanced features available are explained including viewing the noise his tory during the tuning and how to tune only some specific channels Basic checks If the noise level is very high before fine tuning try following operations until the situation looks better Check that the door of the shielded room is closed Check that there is no strong source of disturbance inside the room like a moving patient Loada well known tuning file See About saving and loading 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 the system or helium level may be very low Ifthis does not help you need to contact the system administra tion or to tune manually to find out what is wrong If all channels are mostly out of lock small negative bars check that there is helium in the dewar If not inform the system administrator immediately to prevent system to warm up completely
62. ne ses sion to another class parameter name type description preference DispScaleTrace float I Phi curve scale preference DispOffsTrace float I Phi curve offset preference DispScaleNoise float Noise plot scale preference DispOffsNoise float Noise plot offset preference 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 Scales Testing parameters are used only in internal test mode not in actual use class parameter name type description testing TestMode integer reserved testing TestOffset float reserved testing TestNoise float reserved testing TestLfNoise float reserved testing TestAmp float reserved testing TestSine integer reserved Table B 12 Testing parameters The curve matching parameters are currently not used They are defined for compatibility reasons class parameter name type description measurement CurveMatchDelta integer reserved measurement CurveMatchLimit float reserved measurement CurveMatchMaxTry integer reserved testing CurveMatchVerbose integer reserved Table B 13 Curve match parameters 76 NM21283A B Parameters B The obsolete parameters are defined to make the program backward com patible with o
63. nel or use the slider by the text field The I curve should 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 Setting the expert level on page 43 To measure I Phi curves using Tuner 1 Select Job gt Manual tune from the Tuner menu 2 Press the start button 3 You should now see a bar diagram showing the modulation depths of all channels Select one particular channel to see the I curve 4 To stop the measurements press the stop button The various options available in Tuner are described in more detail in Chapter 8 The information here should be enough to carry on the basic manual tuning 7 5 Measuring noise level Manual tuning process also requires an ability to measure the noise level of a sensor Though the acquisition program does not provide this possi bility explicitly the tuning of the noise level can be made by judging the changes in noise level by eye looking at the raw data display NM21283A B Manual tuning KA To measure the approximate noise level using Squiddler 1 Select Mode gt Meas from the Squiddler menu 2 Use the navigation buttons in the raw data display to show a particular channel on the display To measure the noise level with the Tuner see Measuring the sensor noise level on page 11 The right edge of the n
64. nsist actually of a family of curves for each value of magnetic flux threading the ring However the dependence on the magnetic flux is periodic and it is customary to plot only the extremum curves As the magnetic flux through the ring changes the shape of the current vs voltage curve changes continuously between the two extrema The period with which the behavior repeats itself is one flux quantum 2 07 10 Wb The two extremal curves shown in Figure 6 2 thus correspond to magnetic flux values separated by 2 Near the origin the SQUID is in superconducting state and current can flow through without a voltage loss In Vectorview there is a deliberately added small series resistance which causes a finite slope near the origin as in Figure 6 2 NM21283A B Principles of SQUID operation n NM21283A B Ml B MA Lp L Figure 6 3 a Examples of voltage bias points on I V curve b Flux current characteristics at the example bias points If the bias voltage is set to level V 5 in Figure 6 3 a the current through the SQUID varies as a function of magnetic flux as given by the lowest curve in Figure 6 3 b The sensor remains partly in superconducting state therefore there is a plateau in the current vs flux characteristics At a bias voltage of V p the sensor is biased just above the superconducting state and a maximum modulation depth appears as seen from the middle curve of Figure 6 3
65. nt on page 46 66 NM21283A B Description of full menus 12 NM21283A B Modulation Select the overview of relative modulation depths See I Phi mea surement on page 46 Modulation abs Select the overview of absolute modulation depths See I Phi mea surement on page 46 I V curve Show the last measured I V curve See Measuring and using cur rent voltage characteristics on page 54 Noise Select the white noise level to be shown on the graphics area See 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 on the selected channel or a over view of noises on all of the channels when channel zero is selected See FFT measurement on page 49 Signal Select viewing of signal samples See Signal on page 50 Gate curve Level 2 only Select viewing of noise versus gate setting curve See Measuring gate curves on page 55 DC levels Select the graph showing dc levels of the channels DC level histogram Select the graph showing the dc levels as a histogram Line freq levels Select the line frequency levels to be shown on the graphics area Line freq level histogram Select the graph showing line frequency levels as a histogram Bias history Show history of bias value settings Offset history Show history of offset va
66. of the sensor SQUID when a single channel is selected The overview mode all channels shows a bar diagram where the top and bottom of the bar show the maximum and minimum values of the I curve This view is useful to check that the offset settings of all channels are proper Each bar should cross the zero line so that about one third of the bar is below the line Modulation abs This mode shows the I curves of the sensors same way as the I Phi mode except that in the overview display all bars have been shifted to start from the zero line so that they display the modula tion depth clearly Modulation This mode is similar to Modulation abs except that the modula tion depths 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 bars should have height of exactly 1 0 Any change in modulation depth is easily noticeable This mode is useful for checking the presence of flux trapped SQUIDs and shifts from the nominal operating point 8 6 Noise measurement Another basic operation is to measure the white noise level of the sensors This measurement gives a reasonably good and robust estimate of the noise level with a quick measurement The measurement band is in high frequencies so that normal external disturbances do not affect it much As a further refinement line freq
67. oise history trace shows the current noise level You can also use the raw data display in a similar manner as when using Squiddler 7 6 Manual tuning procedure NM21283A B Manual tuning is a process to set the SQUID operating point parameters to optimal values This section describes this process step by step using the measurement methods described in previous sections Warning Do not adjust gate setting to values below 150 unless the opti mum noise is achieved with a lower value Some FET transistors may alter their characteristics with low bias voltages This manifests as a shift in the optimal gate setting which relaxes in a couple of hours Warning In some Vectorview systems pre amplifiers are capable to deliver signal levels which saturate the inputs of DSP boards enough to cause them to fold the signals Ifthe signal is very noisy and changes to opposite direction than normally when bias or offset is adjusted scan the whole bias offset range to get the signal into normal regime again To tune a sensor manually 1 Set the measurement system into tuning mode using either Squiddler or Tuner 2 Choose the channel to be tuned 3 Adjust the bias voltage to find the maximum modulation depth of the current vs flux characteristics The number in the bias setting 0 255 is proportional to the bias voltage Use the mouse or up and down arrow keys to position the cursor to bias setting field The value can then be enter
68. ory that are shown as possible choices If the mask part after the last slash in specification is character all files in the directory are shown If the mask contains other characters the file names show must contain the same pattern For exam ple specification neuro dacq tuning tnp would select all files in direc tory neuro newdata test that end to string tnp Below the directory specification there are two selection boxes The left one lists all subdirectories to the directory specified above You can change the currently viewed directory easily by double clicking a direc tory name in this list The right list contains all the files matching the directory specification Note that the parent directory is noted by filename ce 7 two dots in these lists 6 NM21283A B User interface basics E NM21283A B Below the lists there is a text field that shows the currently selected file If you must create a new file that does not exist yet you can enter the new 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 selection box You may also select the file name by clicking it once and then pressing the ok button If you need to cancel the ongoing selection press the cancel button on the bottom of the dialog E User interface basics 8 NM21283A B CHAPTER 2 NM21
69. ppendix lists all parameters that can occur in a tuner parameter tnp file The parameters are arranged by their parameter set Each set contain parameters that are or would be displayed in same dialog box The class of a parameter is a tag that is used to group functionally similar parameters together Parameters can for example be loaded per class basis and e g class preferences is saved to a special file Parameter name is the name used in the setup files If the type name contains brackets after the name this means that the parameter is a vector typically one value for each channel If the type contain braces the type is a set of the base type objects The system parameters contain parameters that 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 LineFrequency float Power line frequency of the site Hz system OVLlevel float Overload voltage level V system UseHeNames integer Use helium level in state file names system HeLevels integer List of helium levels used system HeLevelLog string Name of the helium level log file system HeatingTime float How long to heat a sensor s system JanitorService string Janitor service name system JanitorBoot string Janitor boot file name system CurrentPar string Directory for current parameter sett
70. rs The operating point parameters define the nominal operating point and some sensor features at that point class parameter name type description state OpHeLevel integer Helium level at the operating point state OpBias integer Bias setting at the operating point state OpOffs integer Offset setting at the operating point state OpGate integer Gate setting at the operating point state OpFract float I Phi curve fraction at the o p state OpBiasDrift float reserved state OpOffsDrift float reserved Table B 8 operating point parameters The static parameters define sensor characteristics that are independent of the operation point class parameter name type description static OpBtoV float Bias current change per setting unit static OpOtoV float Offset current change per setting unit static GateLow integer reserved static GateHigh integer reserved static OpMod float Modulation depth at o p 74 Table B 9 Static parameters NM21283A B Parameters G class parameter name type description static OpPhi0 float Flux quantum size of a channel static OpNoise float Noise at the operating point static BrokenCh integer Is the channel broken Table B 9 Static parameters The preference parameters define values that are saved separately for each user Color names defined for the
71. s 54 10 4 Measuring gate curves ees 55 Chapter 11 Miscellaneous 56 11 1 Searching channels i225 0 ou a 56 ii NM21283A A 11 2 Loading and saving in special cases 56 11 3 Marking broken channels 2220000 eee eeeee 57 11 4 Reverting operating points 57 11 5 Creating start up files eee 57 11 6 Updating the power up settings 58 11 7 Synchronizing Janitor 0 ccc eee 59 TS USING SSP ana een DR A ees 59 Chapter 12 Description of full menus 61 12 1 File Menu Bst 61 12 2 JOD Men ca se nn ee wes 63 12 3 Parameters Menu cece eee eee 64 12 4 Commands Menu ker e Ra Be 65 12 5 Search Menu r rosenn ieii kerei en E a ai 66 12 6 View MENU 2 oriented 66 12 7 Help Men s Ya she ea 68 Appendix A Command line options 70 Appendix B Parameters 71 Appendix C Revision history 78 NM21283A A iii NM21283A A ao Introduction NM21283A B This manual has two functions It is at the same time the user s manual of the sensor tuning program and also a manual describing the operation principles of Vectorview sensor hardware Detailed descriptions about the SQUID sensor system electronics and tuning principles are given in addition to the description of the tuning program The SQUID tuner program tune_vv is a versatile tool that can be used in maintenance of Vectorview me
72. s loaded Using the command File Save Load current channel only one can load only the operating point parameters of the current channel channel selected to be viewed To save or load only some selected parameters to all of the channels use menu commands File gt Load gt Load selected params or File gt Save gt Save selected params These commands pop up a special file selection dialog button which has a toggle button for each parameter group By selecting and deselecting these buttons one can choose which parameter groups are saved or loaded NM21283A B Miscellaneous ul NM21283A B 11 3 11 4 11 5 Marking broken channels Some channels can be marked broken in the start up files This causes that these channels will automatically behave as if they were marked inactive from the active channels dialog See Tuning selected channels on page 18 The flag indicating a broken channel can be toggled using menu command Commands Toggle broken status The change of the status flag is temporary and affects only the current session unless the settings are saved into the start up file See Section 11 5 Reverting operating points The program has two options to undo tuning settings It is possible either to return to the state which prevailed when the program was started or to the nominal operating point To revert settings to state at program start up time 1 Select File gt Revert to start up state from
73. s parameter name type description measurement Accuracy integer Required accuracy needed to stop relative measurement SettlingTime integer Length of the settling time after parameter changes s measurement LogCh integer Channel to be logged for testing Table B 5 Tuning settings The bias scan settings affect the measurement of I V curves class parameter name type description measurement BiasScanStep integer Step size in bias scans measurement BiasScanlnitialWait integer Settling time in the beginning s measurement BiasScanSettlingTime integer Settling time between measurements s measurement IVPlotBottomScale float Lower y bound for I V plots measurement IVPlotTopScale float Higher y bound for I V plots Table B 6 Bias scan NM21283A B 73 B Parameters The gate scan parameters affect the measurements of noise versus gate setting curves class parameter name type description measurement GateScanStart integer Start value for gate scans measurement GateScanStop integer End value for gate scans measurement GateScanStep integer Step size in gate scans measurement GateScanInitialWait integer Settling time in the beginning of the scan s measurement GateScanSettlingTime integer Settling time between measurements measurement GateFork integer reserved Table B 7 Gate scan paramete
74. t and inaccu rate In such conditions SSP should be used in noise measurements See Section 11 8 on page 59 and Section 8 6 on page 47 If the current v s flux curve shows hysteresis this is most often due to trapped flux in the sensor To cure the problem heat the sensor If this does not help try repeating 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 the zero line was tilted This is most likely due to moisture in the preamplifier connector on the top flange of the dewar To fix this problem the connectors must be dried Tuning is not likely to remove the problem This kind of phenomenon may also be result of other types of hardware failures If the real time signals on raw data display in the normal measurement mode show jumping between two levels also called popcorn noise most likely reason for this is trapped flux To cure the problem heat the sensor If the real time signals show low frequency drifting in a small set of chan nels this may due to oxygen snow in the dewar If this is the case only way to remove the problem is to heat the whole dewar This can be per formed only by skilled maintenance personnel Note that this kind of phe nomenon may also rise due to bad SSP vectors Check carefully the channels both with and without the SSP and compare the behavior to
75. the menus To revert to the previous nominal point of operation 1 Select File gt Revert to previous o p from the menus 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 loads four files in fol lowing order neuro dacq tuning system tnp start up script may alter this name neuro dacq tuning static tnp may be altered in the previous file Current operating point file deduced from the helium level tuneprefs containing the personal preference settings SUNT The first one is intended for fixed measurement parameters etc and it gives default values for all parameters defined in the file It should not be altered unless there is a need to permanently change the default values Usually the file delivered with the system should be ok The second one is a file that should contain values for static parameters that is parameters that are assumed to be independent from the operating point but which vary from device to device From this file only parame ters in classes static and state are loaded so it may contain also other parameters which are neglected See Appendix B 57 ul Miscellaneous 58 The static file needs to be generated for each system after any larger maintenance operation like changing an electronics board or a sensor Before saving the file the system should be tuned an
76. til the measurement ends NM21283A B 55 ul Miscellaneous cHAPTER 11 Miscellaneous 56 This chapter describes some miscellaneous operations related to searching channels settings files and Janitor program Searching channels The program offers several search routines to search channels for some particular feature Following searches can be performed from the Search menu Worst offset Find channel whose I curve crosses zero line at a level that differs most from the value defined for the current working point Worst noise Find channel having largest white noise level Weird Phi0 Find channel whose flux quantum size differs most from the other channels Next Find next worst channel Before this command one of the first three commands must be issued to select which parameter should be searched 11 2 Loading and saving in special cases In addition to normal saving and loading of tuning 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 the preference parameters The normal File Load tunings loads only operating point parameters all other parameters are neglected Therefore one can for example check from a tuning file what kind of measurement settings were used when the file was made but these measurement set tings do not affect the current settings when the file i
77. to saving and loading of the internal state of the program and the measurement device Load tunings This button enables you to load magnetometer state from a file The file must be in the tuner format tnp Using this command only the state parameters are loaded all the rest of the information in the file is discarded If you need to load some other information use Load gt 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 sets the current operating point information within the program to values being used at the saving time See About saving and loading settings on page 14 Revert to previous 0 p This button returns the magnetometer tuning state to the current tuning state This state reflects the state of the magnetometer at the time when the program was started or the state specified in the parameter file last loaded or saved See Reverting operating points on page 57 Revert to start up state This button returns the magnetometer tuning state to the state that was prevailing when the tuner program was started It undoes all 61 12 Description of full menus 62 changes made by the tuning program See Reverting operating points on page 57 Load gt Current channel only Load settings of the currently selected channel only See Loading and saving in special cases on pa
78. tton is released the corresponding action will be executed and the menu disap pears You may also activate a menu button by pressing the mouse button on the name of the menu holding the button down and dragging it on top of the desired button The action is now executed when the button is released on the menu item If you pop up a menu accidentally you can cancel the operation by releasing the mouse button when cursor is outside the menu or if you clicked the name by clicking somewhere outside the menu Some menus contain so called submenus They are connected to menu buttons whose activation pops up yet another menu The submenu itself is used just similar fashion as a normal menu Submenus are denoted by a small triangle on the left edge of a menu button Using text fields Several user interface elements use so called text fields or text boxes This is a rectangle that contains some editable text inside E User interface basics To enter some new text into an empty field click the rectangle to get the active text insertion point so called text focus into the desired text field Then use keyboard to enter whatever text that is needed If the text editor has multiple lines use return key to start a new line Notice that in single line text fields pressing the return key may case some execution to occur In several dialogs it is equivalent of pressing the default button of the dia log If you need to alter all or some text in
79. uency disturbances are filtered away from the data This mode is a tool that can be used to check quickly the quality of the data on all channels It is also a building block used in all noise optimiza tion jobs In addition to white noise level this job measures also the dc NM21283A B 47 H Basic measurements level and line frequency disturbance amplitude on each channel The parameters affecting the noise measurements are shown in table Table 8 2 Parameter Type Description NoiseHpf float High pass filter corner frequency Hz NoiseLpf float Low pass filter corner frequency Hz NoiseSfreq float Sampling frequency Hz NoiseNAve integer Number of averages NoiseSsp Oorl IsSSP used IgnoreAfterReset integer How many buffers to ignore after reset GoodEnough float Noise level regarded as good enough Table 8 2 Parameters affecting noise measurements The noise measurement results can be displayed using following view modes Noise This mode shows the sensor white noise level Overview shows a bar for each channel showing the noise Single channel view shows the noise history results of previous measurements within the ses sion Noise histogram This mode is similar to Noise mode except that the overview 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
80. uning NM21283A B Figure 7 2 Gate tuning If the system has been tuned earlier start from the current value of the gate setting Otherwise start from 150 Increase the value by the right arrow key The noise on the falling slope diminishes see Figure 7 2 b until an irregularity appears as in Figure 7 2 c Stop increasing the gate at that point In the actual SQUID the noise might be difficult to distinguish on the 10V scale the appearance of a hump in the current vs flux characteristics is a clear sign indicat 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 smooth Adjust the offset voltage so that approximately one quarter of the cur rent vs flux characteristics is below the zero line and three quarters above it See Figure 7 3 c Change Squiddler Tuner settings to make a noise measurement Now you should see a signal trace on the raw data display screen or the noise level trace of Tuner The noise seen should be minimized by fine tuning the gate and offset At this point you can either use automatic 37 E Manual tuning 4 k 5 Pe tsa See Pe Snes sae nn PSs Si Sapa oe Poe os ese aaa Peer Here een Figure 7 3 Offset tuning fine tuning See Fin
81. utton 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 during active measurements so if the menu is unavailable you must stop the ongoing measurement by pressing the stop button It is recom mended that you exit the program after checking the noise levels or tuning before starting a new acquisition NM21283A B CHAPTER 3 NM21283A B 3 1 Basic tuning operations This chapter explains how to measure white noise level of the sensors automatic fine tuning and heating of the sensors Measuring the sensor noise level The tuner program can be used to check the white noise level of all the sensors This can be done before the measurements to check that all chan nels are working properly To measure white noise levels using Tuner 1 Stop any ongoing acquisition by pressing stop button of the acquisition program and wait for the measurement to stop 2 Start the tuning program if not running yet See Beginning a ses sion on page 9 3 Press the large Measure noise button on the left Warning If there was a measurement running when the tuner was started the start button is gray and no tuner measurements can be initi ated In this case one must exit the tuner stop the normal acquisition measurement and then restart the tuner again Warning Acquisitio
82. ws access to several oper ations and parameter settings Major part of the window area is taken by a graphics area which is used to show the results of current operation On the left are controls to show and alter manually the SQUID working point parameters and two large buttons that are used to initiate and stop opera tions These buttons will be called start button and stop button throughout the manual The labels on these buttons change depending on the situation In the bottom of the window is a status display area and con trols to alter graphics display scales E Getting started Working point controls View channel Start button Stop button State icons The status display area is divided in four regions described here from left to right The leftmost small icons show the state of the acquisition Area showing current helium level in the dewar Status message area which shows information about ongoing activities Information area showing variable user data like cursor position Scale controls of the graphics display Noise level Tue An 13130230 200 Average SALA Graphics area id 5 i i B E A M 1 z T 16 Charnel nuber Bois Ro i 189 1 Helium level Status text area Information area Graphics controls Figure 2 1 Main window of the SQUID tuning program 2 2 Using online HELP 10 The Help menu contains currently only a b
83. x 2005 03 13 3rd edition NM21283A B tune_vv 3 2 x 2009 05 18 NM21283A B Contents NM21283A A Introduction 1 Part 1 Basic Usage Chapter 1 User interface basics 5 1 1 Using mens Mut De a Gk RR 5 1 2 Using text fields nn nr esate Ron n 5 1 3 Using file selection boxes 6 Chapter 2 Getting started 9 2 1 Beginning a session nn nn 9 2 2 Using online HELP or ae ari 10 2 3 Ending a session sop te eda eS RE RIA REA 10 Chapter 3 Basic tuning operations 11 3 1 Measuring the sensor noise level 11 3 2 Fine TUNING eo Ere exea p wei Ee CR IW ee ee 12 3 3 Resetting channels nenn nn nn 13 3 4 Healing Sensors 2 2 13 3 5 About saving and loading settings 14 3 6 Noise display iaia boiata 15 Chapter 4 Troubleshooting 17 4 1 Basic CHECKS zi ER ie a Ea PK 17 4 2 Viewing noise history of a channel 17 4 3 Tuning selected channels 18 Chapter 5 Description of the menus 21 51 File Menu 4 xus iuc E er 21 5 2 Parameters Menu ll rr ras 21 5 3 Commands Menu esses 22 5 4 Search Menu ers fasia Di ge memei ERES x msan a 22 5 5 View Menu seges ee E NA 23 5 0 Help Menu siii 2 Sones ni het 23 Part 2 Sensor operation principles Chapter 6 Principles of SQUID operation 27 6 1 Operation of a SQUID magnetometer 27 6 2 SQUID electroni

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