Brandes, J.

Friesinger, G.

Ulbricht, A.

English

KITopen

May 1970Institut für Experimentelle KernphysikInstitut für Datenverarbeitung in der TechnikKFK 1220An Arrangement for Automatie Magnetie Field MeasurementsJ. Brandes, G. Friesinger, A. Ulbricht,,~ ,Als Manuskript vervielfältigtFür diesen Bericht behalten wir uns alle Rechte vorGESELLSCHAFT FüR KERNFORSCHUNG M.B.H.KARLSRUHE••May 197()KERNFORSCHUNGS ZENTRUM KARLSRUHEKFK 1220Institut für Experimentelle KernphysikInstitut für Datenverarbeitung in der Technik (*)An Arrangement for Automatie Magnetie FieldMeasurements+J. Brandes (*)G. FriesingerA. UlbriehtGESELLSCHAFT FÜR Y~RNFORSCHUNG MBH., KARLSRUHE+Paper presented at the 111. International Conferenee on MagnetTeehnology, May 19-22, 1970 HamburgZusammenfassungEs wurde eine Apparatur zur automatischen Ausmessung von Magnet-feldern entwickelt. Diese kann für die Ausmessung von Biege-,Quadrupol- und Gradientenmagneten bis zu Feldstärken von 50 krmit einer Genauigkeit von 1%0 verwendet werden. Die Feldstärkewird mit Hallsonden, Spulen oder magnetfeldabhängigen Wider-ständen gemessen. Die Sonden werden durch eine spezielle Meß-maschine im Feld mit einer Genauigkeit von ± 10~m positioniert.Alle Gleitlager der Maschine sind zur Wahrung der Genauigkeitund zur Vermeidung des Stick-slip-Effektes statische Luftlager.Zur Steuerung der Maschine und zur Verarbeitung der Daten istäiese im On-line-Betrieb an einen TR8G Rechner angeschlossen.An Arrangement for Automatie I"IagneticField I"IeasurementsJ. Brandes, G. Friesinger, A. Ulbricht·Kernforschungszentrum KarlsruheAbstractAn arrangement for automatie magnetic field measurements is deve-loped. It can be used for bending, quadrupol and gradient magnetswith field strength up to 50 kG within 0.1 %and assists the de-velopment of synchrotron and beam transport magnets. The measure-ment is done with Hall probes, coils or field depending resistors.The magnetic field sensors are positioned by a specially construc-ted measuring machine within ± 10 /um. All slide bearings are sta-tic air bearings to avoid stick slip and wear and tear. For auto-matie acquisition of the high quantities of data and for on-linecontrol of the measurements, the measuring system is connected toa TR 86 computer.- 2 -I. IntroductionFor the development of synchrotron and beam transport magnets anarrangement is developed for measuring the field distribution ofbending, quadrupol and gradient magnets (1,2,3). The magneticfield is measured point by point and all necessary derivations,gradients, differences etc. are computed from the obtained data.The apparatus, which is connected to a TR 86 computer for on-linedata acquisition and control, consists of three parts:The mea-suring device, the driving mechanism for positioning the magneticfield sensors, and the electronical equipment for data trans-mission and control of the measuring process.11. Magnetic Field SensorsThe magnetic field sensors are Hall plates or magnetic field de-pending resistors for static and coils for dynamic field measure-ments. A temperature stabilized Hall plate with aprecision cur-rent source (stability 2-10-5 in 8 hours) yields together withan analog-to-digital converter an accuracy of 10-4 • The coils fordynamic measurements are described in a proceeding paper (Lt ).The magnetic field sensor is mounted on the top of the arm of themeasuring machine (fig.1). The measurements are point measure-ments and all further computations are done by a computer. Thispresents a considerable flexibility for the various measure-ments of quadrupole, bending and gradient magnets. With thehigh accuracy of the measurements required, the strong gradientsof the fringing fields and the magnetic fields themselves de-mand some effort for positioning the probe precisely enough inthe field. Requiring an accuracy of 2 Gauss at gradients in theorder of 3 kGauss/cm the probe must be positioned with an accuracybetter than ± 10 /um.- 3 -Fig.1The positioning machine with the manual control desk.\Fig.2The carriage with mountedz-pillar supported on fourair lubricated flat bearings.3a volume of 2,0 x 0,5 x 0,3 m •at (22,0 ~ 0,5)OC.- 4 -simple manner with stepping motors. The accuracy of the guidancedoes not decrease, because no wear and tear arises, which in anideal condition for a measuring apparatus.The mechanical construction, done in cooperation of three firms,is described in the following (6). The measuring magnet and themeasuring machine are mounted on one foundation. The basis ofthe positioning machine is a plate of black granite (dimensions:3,6 x 1,5 x 0,45 m3 ) placed on a three point support (7) (fig.1).The surface of the granite plate is lapped within ± 6 /um. Theguidance for the s-direction is a groove in which one bar ofa rectangular cross slides. The other bar of the cross is theguide rail in x-direction. A carriage, supported on four air lub-ricated flat bearings, slides on the stone surface and is guided bythe bars of the rectangular cross to every point in the s-x-plane(fig.2). A quadratic pillar is mounted on the carriage. The move-ment in the third dimension, the z-direction, is done by a sleevesliding on the pillar. A spindle rests in a circular air bearingwhich is mounted on the sleeve. The probe holder is fastened withclamps at the top of the spindle. The spindle and therefore the·probe is able to be rotated around its longitudinal axis aboutan optional angle within ± 20 arcsec. The pillar of the carriageis adjustable in the z-direction. The angle error of the Carthe~sian coordinate system s,x,z is smaller than 2 arcseconds. Besidesthis, the pillar has an air lubricated thrust bearing and fromthat it is turnable around the z-axis within 3600 • This allowsmeasurements with different magnets, placed near the positioningmachine.The measured accuracy of the guidance for the s-direction iswithin ± 6/um (fig.3). The deviation from the straight linealong the x-direction is smaller than ± 6 /um in the verticalplane and ± 0,15 /um in the horizontal plane. The deviation ofthe z-direction is within ± 0,15 /um (fig.4).The positions of the probe are read photoelectrically by a binarycoded measuring device with an accuracy of : 5 /um (9). One stepof the stepping motors corresponds to a movement of about 1,5 /umalong one coordinate (max.stepping rate 3200 puls./sec and 2000steps/rev.) (8).The probe itself can be positioned inThe measuring room is air conditioned- 5 -The measured deviation trom the straight lineat the surface of the granite plates [mrnJ.3000 3 0020001000+10o~~.4=+==:=:::::::::::t=::=::=~>==9~t:::::-+i-10 100 500Granite plateFig.3The measured deviation trom the straight line, when the carriage ismoved along the x - axis:fJJmJl11 s+ 0,2o ~"""""""'.............-:I 1 .......... ------ 0,2 100 200 300 400 500The measured deviation trom the straight line,when the sleeve is moved along the z - axis:x Ij-nrrj).z CrnrnJ •z rmrnJ•/jJmJF-lls+0,2_o --====------r4f=~-~~-==-""'f=====--""""~~- 0,2 100 200 300~rnJ~X+ 02 _o """"-:"....".,.,.,,===~I=---.----==;;:::::::;;;;........._---==,--==-;- =~==......-~~--=-,- 0,2 100 200 300Fig.4~ 6 -IV. The Electronical Equipment for On-Line Control and DataAcquisitionFor the on-line control and the data acquisition of the magneticfield measuring system a TR 86 computer configuration is used. TheTR 86 system is planed for serving several other experiments bytime sharing, too, and consists of an usual computer configurationwith peripheral standard units completed by a data channel and CRTdisplay facilities (10).The data channel is developed for transmission of commands anddata with rates up to 2.5 kHz towards the special electronicalequipment of the experiment.The experimental electronics (fig.5) consists of a HP 2402 ADC,the ADC scanner to serve up to 6 measuring places, the scannerunit to adress the s,x,z and ~ registers, which contain the infor-mation about the probe position, and the units to drive the probein the s,x,z and j directions (11) (12). A wanted position isreached, when apreset register is counted down. This causes aprogram interrupt in the TR 86 computer. In the same way the endof conversion of the ADC is signaled to the computer via the datachannel.The command unit enables the experimentator to start certainprograms as well as to input required parameters. Because theoperating system of the TR 86 allows time slicing, it is possibleto run several routines together.Adjusting operations can be carried out by a manual control desk.The desk allows driving of the magnetic sensors by hand and dis-plays its position on numeral indicator tubes as decimal numbers (14).V. Software of the Automatic Field MeasurementsThe tasks, the software has to achieve, are to control the measu-ring device, to transput the measurement values and to store themon magnetic tape and disk, as well as further data processing anddisplay.The required hardware is described above. Besides this a completeTR 86 operating system for multi access exists, which contains7D MEASURING ROOMCOMMAND BUSBlock diagram of the electronical equipment.xFig.6Geometrical parameters of the meanderroutine.8 -NOEND 4COMPUTATION OF A DC VALUESCOMPUTATION OF REAL POSITIONINPUT: CONTENT OF S-,X-,Z-,f- AND ADC - REGISTERSNUMBER OF DRIVING STEP5:= THEOR. POS. - REAL POS.OUTPUT: DRIVING COMMANDS, COMMANDS FOR ADC ANDADC SCANNER, READ REGISTER COMMANDSTHEOR.POS.:=X: .N,' 6X: • Ai..J CALIBRATIONrL PHASEP= 2P=3NO(X,S.Z IOUTPUT: PROBE POSITION AND ADC - VALUES ON MAGN. TAPEU HALL VALUES ON DISKSU BGE~COMPUTATION OF N~,N~ ANDax:,olIx: i= 1,2,3 FROMP"P"P, AND d, .d,· (s.TEXT)INPUT PARAMETERS: Bo ,.6BADC VALUE: U HALLCOMPUTATION OF UHALL =f (B = Bo' n ·.6B I,OUTPUT ON MAGN, TAPEAND DISK,J MEASUREMENTP=4 f1 PHASEFig.7Flowchart of the meander routine.- 9 -macro-instructions for the peripheral standard units (10) (13).Therefore the data output on magnetic tape (for further processingon the IBM 360/65) and the transput on disk (for further processingon the TR 86) is quite easy, but about 2000 TR 86 commands are re-quired for driving the Hall probe on a meandering line.The complete software consists of three driving programs (themeander program, below described in detail, and two circular pro-grams) with a calibration and measurement phase, several analysisroutines with CRT display of the results, and later on the soft-ware for more sophisticated analysis with the IBM 360/65.The analysis programs of the TR 86 display the functions:BBo-B == f (s,x,z)~) == f (xi, i == 1 ••• 4)odB--dx j== f (xi, i == 1 ••• 4), j 1 ••• 3 and== 1 ••• 4)== f (xi, i+00== magnetic field, s,x,z, cP == the coordinates and L == ~o ~ B dxi •- ...,with BThe route points, the probe has to cross, are illustrated for themeander routine in fig.6 •. The flowchart of the meander routine isrepresented in fig.7. This routine requires five geometricalparameters:The coordinates of P1, P2' P3' which define the plane of the mean-dering line and d1 and d2' which fix the distance of the routepoints (s.fig.6). With these the subroutine BGEO computes the=--'=-number N1 , N2 of duty steps, the probe has to drive towards P1P2and P2P3 as:Ni == entire (Pi Pi +1/di ), i == 1,2 ,and the components (6 s, ~z, .6x) == (..6 xi, i == 1,2,3), which arenecessary, because there are only driving commands in the s,z,x(and?) directions. In fig.7 the adjustment phase 1 means theinput of control parameters, like the number of ADC measuringpoints and their units. In adjustment phase 2 it is assumed, that- 10 -Fig.8a) An isometrie display of a measured field distribution in onehalf of a bending magnet with circular pole faces. The probeis driven along a meandering line which lies parallel to thepole faces in the middle of the air gap.(vertical: field error dB ~ (Bo - B)/Bo , 7%/div.; horizontal:3,6 cm/div. i distance of two curves: 0,9 cmj Bo = 22 kGauss). b) The medium part of the first curve in Fig.8a) drawn in a largerscale. (vertical: field error dB, 7 p 10-5/div.; horizontal:0,94 cm/div.; Bo = 22 kGauss)(- 11 -the Hall probe is driven by hand to points P1 ' P2 and P3' oneafter the other and the phase 2 started each time again.The points P" i = 1 ••• 3, are optional; if two of them are iden-ltical, the probe is driven on a line. All further details can beseen from the flowchart.Fig.8a) shows the isometrie display of the field distribution inone half of a bending magnet with circular pole faces. The eightmedium points of curve 1 are drawn in a larger scale in Fig.8b).VI. ConclusionsThe arrangement for automatie magnetic field measurements is des-cribed in its intermediate state. The connection of the apparatusto a TR 86 computer effects an highly flexible field measuringsystem. The software for on-line control and fordata processingis designed for a lot of different measuring problems. B,y meansof a display unit, the results of the measurements can be re-viewed by the operator in the measuring room and therefore acontinuous supervision of the measuring process is possible, whichis important for the measurements of larger series of magnets.References(1) Vorschlag zum Bau eines 40 GeV Protonensynchrotrons, Kern-forschungszentrum Karlsruhe, Inst. f. Exper. Kernphysik,Juli 1967(2) Addendum to (1), Kernforschungszentrum Karlsruhe, Inst. f.Exper. Kernphysik, Juli 1969(3) G. Bogner, H. Kuckuck, D. Kullmann, N. Fessler,A 12 cm Bore Superconducting DC Quadrupole Lens,Conference on Magnet Technology, Hamburg 1970(4) H. Schmidt, P. Sack,Automatie Dynamie Field Measuring System,Conference on Magnet Technology, Hamburg 197012(5) K. Holm, K.G. Steffen,Beam Transport Magnet Mesaurements at DESY,Proc. Int. Symp. on Magnet Technology 1965, 456-466.(6) FAG, Schweinfurt; MAN Augsburg; Rank Taylor Hobsen Nürnberg(7) Collins Microflat, Los Angeles, Calif., USA(8) Harmonie Drive Division United Shoe Machinery,Corp. Beverly, Mass., USA(9) Dr. Joh. Heidenhain, Traunreut(10) G. Gagel, H. Herbstreith, G. Hepke, J. Nehmer,KFK-Ext.-19/69-1 (November 1970).(11) J. Ottes, W. Stiefel, Steuerelektronik für automatischeMagnetfeldmaßapparatur, (April 1970, unpublished)(12) M. Urbanetz, Funktionsbeschreibung der speziellen Elektronikfür das Experiment IEKP I, (April 1970, unpublished)(13) G. Krüger, KFK-Bericht 929 (Jan. 1969).(14) J. Ottes, Code-Umsetzer, ELEKTRONIK, 19 (1970) 73-78,KFK-Bericht 1185 (März 1970).

An Arrangement for Automatic Magnetic Field Measurements

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An Arrangement for Automatic Magnetic Field Measurements

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