A new system for precise measurements of the field integrals and multipole
components of the APS magnetic insertion devices is described. A stretched coil
is used to measure magnetic field characteristics. The hardware includes a
number of servomotors to move (translate or rotate) the coil and a fast data
acquisition board to measure the coil signal. A PC under Linux is used as a
control workstation. The user interface is written as a Tcl/tk script. The
hardware is accessed from the script through a shared C-library. A description
of the hardware system and the control program is given.Comment: 3 pages, 5 figures, paper 3271 submitted to ICALEPCS 2001 Conferenc

Deriy, B.

Eidelman, Yu.

Makarov, O.

Vasserman, I.

English

arXiv

A new system for precise measurements of the field integrals and multipole components of the APS magnetic insertion devices is described. A stretched coil is used to measure magnetic field characteristics. The hardware includes a number of servomotors to move (translate or rotate) the coil and a fast data acquisition board to measure the coil signal. A PC under Linux is used as a control workstation. The user interface is written as a Tcl/tk script; the hardware is accessed from the script through a shared C-library. A description of the hardware system and the control program is given

Eidelman, Y.

UNT Digital Library

PSN: 3271THE NEW MAGNETIC MEASUREMENT SYSTEM AT THE ADVANCEDPHOTON SOURCE ∗Y. Eidelman, B. Deriy, O. Makarov, I. Vasserman,Argonne National Laboratory, Argonne, IL 60439, USAAbstractA new system for precise measurements of the field inte-grals and multipole components of the APS magnetic inser-tion devices is described. A stretched coil is used to mea-sure magnetic field characteristics. The hardware includesa number of servomotors to move (translate or rotate) thecoil and a fast data acquisition board to measure the coilsignal. A PC under Linux is used as a control workstation.The user interface is written as a Tcl/tk script; the hard-ware is accessed from the script through a shared C-library.A description of the hardware system and the control pro-gram is given.1 INTRODUCTIONA new system for precise measurements of magnetic fieldintegrals and multipole components of different types of in-sertion devices (IDs) is created as an upgrade of the Mag-netic Measurement Facility at the APS [1]. The main rea-sons for upgrading the existing system were:• To increase accuracy and reproducibility of acquireddata. Long cables between motor drives and steppermotors in the existing system produce an excessivenoise interfering with the measured signal. Integra-tors in the existing system take 4 data values per coilturn. The new system uses ≈ 1000 data points of coilsignal for analysis, leading to better accuracy. Differ-ent error sources presented in the coil signal can beanalyzed, particularly coil vibrations.• To simplify the system and increase reliability forease of maintenance, future developments, and possi-ble duplication of the system in other projects. In theexisting system VME, Euro, as well as nonstandardcrates, have been used. It has been very hard to main-tain and almost impossible to reproduce the system.• To allow integration of the results of the magneticmeasurements with other APS databases and utilities.The Linux OS instead of Windows has to be used inorder to reuse software modules developed by the Op-erations Analysis Group [2] for the APS storage ring.• To provide more convenient data analysis in bothstand-alone and network operation.• To add more features, such as a translation mode, formeasuring multipole magnetic field components.∗Supported by the U.S.Dept. of Energy, BES, Office of Science, underContract No. W-31-109-Eng-38.2 PRINCIPLE OF THEMEASUREMENTSThe stretched coil is used to measure magnetic field inte-grals. The coil signal is proportional to the time deriva-tive of the magnetic flux through the coil cross section.The measurements are performed at constant coil rotation(translation) speed. There are four different options formeasurements.Integrals and rotation modes. Signals are measuredfor full turns of the coil. Two turns [clockwise (CW) andcounter-clockwise (CCW)] are performed to exclude sys-tematic errors. The measured data are applied to calcu-late absolute values of the first or the second (if the coil istwisted by 180◦ [3]) magnetic field integrals. A set of ap-proximately ten points across the gap of the ID is measuredto calculate multipole magnetic moments.Translation mode. The linear motion of the coil to mea-sure the magnetic flux changing in the horizontal or verti-cal direction is examinated, allowing significant reductionin the measurement time of the multipole moments.Variable field mode. The coil does not move. This modeis designed for measurements of IDs with switching elec-tromagnets [4].3 HARDWARE DESCRIPTIONA block diagram of the new system is shown in Fig. 1.Eight smart motors from Animatics Corp. [5] are used.CoilPCI  DAQPD2-MFS-500/16AmplifierComputerServomotorsx y z wServomotorswx y zRS-232/RS-485ConverterPower Supply Power SupplyFigure 1: Layout of the upgraded system.Each servomotor has an encoder, a motor drive, and a mo-tor controller—all integrated in one unit, thus reducing thelevel of the electrical noise, compared to the existing sys-tem. These smart motors have two standard serial ports—RS-232 and RS-485. All motors connected in parallel tothe RS-485 communication line are controlled by the Pen-tium III computer under Linux OS through a RS-232/RS-485 converter.The stretched coil conventional configuration with parallelwires is being used for measurements of the first field in-tegrals and multipole components. The measured signal isamplified by a SCXI-1120 National Instruments amplifier.The gain is set to 2000, and the bandwidth is set to 10 kHz.A 500 kHz data acquisition board PD2-MFS-500/16 fromUnited Electronics Industries [6] is used to measure the am-plified signal. The Linux driver for this PCI DAQ boardwas provided by the manufacturer.4 SOFTWARE DESCRIPTIONA new Multipoles & Integrals—Software System (MISS)has been written. It consists of two parts: a Tcl/tk scriptand a shared C-library.4.1 Tcl/tk scriptThe Tcl/tk script describes a user interface and data pro-cessing and uses a shared C-library for hardware access.The script language includes all embedded instruments tocreate the user-friendly interface and to use a shared C-libraries. Besides, MISS uses utilities developed by theAPS Computer Support Group for this language. MISS op-erates under Linux and provides the user interface throughthe set of windows and worksheets (see Fig. 2).Data ProcessingSet OriginHand OperatedMeasurement TestLoadCharts"MISS"windowRunWorksheetswindowWorksheets IntegralsRotationTranslationVariable Field"Options"ServiceswindowwindowService""Motor"Motion""Select File"windowMain MenuFigure 2: Software chartflow diagram.Figures 3 and 4 demonstrate examples of the user interface.4.2 Shared C-libraryThe hardware is accessed from the script through a sharedC-library. This library consists of two command sets—onefor smart motors and another for the DAQ board. The serialport driver ”ttyS” with appropriate setting of the structure”termios” is used to control the motors. The Linux driver”pwrdaq” is used to control the DAQ board. Some of theFigure 3: Window ”Motor Service.”DAQ board commands are based on the corresponding C-functions of this driver. The complex procedures providingsynchronization between coil motion and data acquisitionare included in the C-library. These procedures combinecalls to the motors and the DAQ board in the required se-quence. So, the execution of such commands cannot beinterrupted by a Tcl/tk script command.5 SYNCHRONIZATION OF THE COILMOTION AND DATA ACQUISITIONThis process includes two steps.Integrals and rotation modes. At the first step, the choiceof coil ”trajectory” (velocity and acceleration of the ro-tation) determines the calculated delay between initiatingthe coil motion and starting the data acquisition. The sec-ond step includes matching the additional delay to achieveagreement between the signals measured for CW and CCWcoil turns. This matching is based on the assumption thatplots of measured signals (voltage versus the coil’s turn an-gle α) for both of these rotations must be mirror symmetric,if delays are chosen correctly. Figure 5 shows the measuredsignals for both cases after integration and subtraction ofoffsets. It was found that the additional delay is equal to25 ms for a calculated delay of 550 ms.Translation mode. The first step is identical to the firststep in the rotation mode. The additional delay was deter-mined by using the rotation mode with the same velocityand acceleration of the smart motors. This delay is equal to35 ms for a calculated delay of 1500 ms.Figure 4: Worksheet ”Translation” of the window ”Options.”Figure 5: Integrals of measured signals for calculated (left)and matched (right) starts of the data acquisition.6 DATA PROCESSING AND SOMERESULTSDifferent algorithms are used to obtain the magnetic prop-erties of the IDs.A) Measuring of the first and second integrals includes thefollowing steps:1. Fitting of the functions Ai sin(α + φi) on noisy coilsignals for CW (i = 1) and CCW coil (i = 2) turns.2. Calculating of magnetic field integrals Ix, Iy for eachcoil turn from fitting parameters Ai, φi.3. Repetition of previous steps to improve accuracy anddefine rms errors of measurements.The statistical error of integrals Ix, Iy (measured for theEarth’s magnetic field) is equal to ± 0.4 Gs·cm (improvedfrom ± 2 Gs·cm before upgrading).B) Measuring of the integrated multipole moments in therotation mode includes all steps from case A) for a set ofpoints ri across the ID gap and, after that:4. Fitting of the polynomials∑nk=0 bkrk of the power non the sets I(r) (separately for arrays Ix and Iy).Coefficients bk are integrated multipole moments.C) Measuring of the integrated multipole moments in thetranslation mode includes:1. Fitting of the polynomials∑nk=0 bkrk of the power non noisy signals for a few coil passes across the gapof the ID.2. Averaging of obtained coefficients bk over the set ofcoil passes to reduce the statistical errors.Note, that the translation mode saves significant time inmeasuring the integrated multipole moments in compari-son with the rotation mode. Measurements have to be donefor both horizontal and vertical coil orientations.A strong short magnet was used to evaluate the accuracyof the measurements of the multipole moments. Table 1shows these results which were obtained for the translationmode.Table 1: Multipole moments measurements.k bk δbk Units0 652.8 ±0.1 Gs·cm1 2208 ±2 Gs2 1840 ±7 Gs·cm−13 -1167 ±48 Gs·cm−24 -2929 ±127 Gs·cm−35 1985 ±203 Gs·cm−46 460 ±518 Gs·cm−5A few programs from the SDDS Toolkit [7] are usedfor polynomial fitting, data management, and displayingcharts.7 REFERENCES[1] L. Burkel et al., ”The Insertion Device Magnetic Measure-ment Facility: Prototype and Operational Procedures,” Ar-gonne National Laboratory Report No. ANL/APS/TB-12,March 1993.[2] http://www.aps.anl.gov/asd/oag[3] D. Frachon et al., ”Magnetic Measurements of the EllipticalMultipole Wiggler Prototype,” Argonne National LaboratoryReport No. ANL/APS/TB-22, March 1995.[4] E. Gluskin et al., ”An Electromagnetic Helical Undulator forPolarized X-rays,” AIP Conf. Proc.: Synchrotron RadiationInstrumentation, vol. 521, P. Pianetta, J. Arthur, and S. Bren-nan, eds., AIP (2000) pp. 344–347.[5] http://www.smartmotor.com.[6] http://www.PowerDAQ.com.[7] http://www.aps.anl.gov/asd/oag/manuals/SDDStoolkit/SDDStoolkit.html

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