A Multifunctional Magnetic Measurement Control Systemfor NSRL Magnets
Lianguan Shen Zexu Qian

Zhenhua Huang

Qunce Liu

Chengui Yao*

Department of Precision Machinery & Precision Instrumentation
University of Science & Technology of China* National Synchrotron Radiation Laboratory
96 Jinzhai Lu, Hefei 230026, Anhui, China

Abstract
A new integrated multifunctional magnetic measurement
control and data analysis system has been developed,
which can be applied for dipole, multipole, undulator andother magnetic devices. The system was well running formeasuring and shimming an undulator of more than 2meters long which has been installed in HLS storage ring.
1. Introduction
A new version of magnetic measurement facility isnecessary to meet the Project Phase II of NSRL. The NSRL
possessed a discrete magnetic measurement system. In thesystem the FUNAC dedicated microcomputer acted as theposition controller and two other computers were used forsystem manager and data acquisition. They are damaged
now , but a 2-D mapping machine.
The new system is an intensive unit. An IPC(IndustrialPC) is adopted as Central controller and system manager.
All interface cards for control and data acquisition areinstalled on its passive backplane. As an economicalconsideration, a semi-closed loop is accepted as thepositioning control system. Its positioning accuracy is goodenough for most of magnets. But for some special objects,
just like undulator, it can’t fit their requirement on thepositioning resolution. In the case of introducing a laser
measurement device , a fine positioning resolution of
0.0001 mm has been obtained.
The efforts in software for improving positioning
accuracy have been made. With the result that themeasurement system is suitable for most kinds of magnetsof the NSRL. The system has been used for detailed
investigating and shimming an undulator of more than 2
meters long, which has been installed in the HLS. The
result shows the measurement system of a high level ofperformance at an affordable price.
2. Utilization of IPC and PC-based control card
IPCs can be used for high level control, relying on
PLCs for the tasks, such as physical-level control andmeasurement. IPCs have the reliability and flexibility tostand alongside PLC system and provide a variety ofservices such as data management ,worker-to machineinterfacing ,monitoring and hardware/software supports.
Serial interfaces or local area networks provide
communication with mainframes or PLCs.
Compared with commercial PC, the IPC has been

designed specifically for more reliable operation in hostileenvironments of electrical noise, electrical interference andpower surge. IPCs chassis holds more slots on its PC-bus
compatible passive backplane than commercial PC, inaddition, spare arts for IPCs are usually standard PC spares,.
It makes possible to form a more efficient, inexpensive andeasy to upgrade.
Figure 1 is the block diagram of the magnetic
measurement control and data management system.
As the figure shows, a PC-based 3-axis servo motor
control card is the positioning controller joining with3-Axis Servo
motor positioncontroller

D I/O andRelay actuator

encodervelocity
controller

motor
X,Z

motor encoder
rotating coil

16 bit A/D

IPC-

16 bit D/Adigitalintegrator

610

rotating
coil
integralcoil

RS - 232
Hall probe
frequency
meter
laser
measurement
deviceIEEE 488

network board

digital volt
meter

DCCT formultipoledigital volt
meter

DCCT fordipoleFig. 1 Block diagram of magnetic measurement system.
the FUNAC velocity controller and the rotating encoder toform a semi-closed controller for the servo motors of themapping machine.
IPC together with the PC-based 3-axis servo motor
control card have given greatly improved flexibility.

Powerful high-level languages are readily available forcontrol and measurement avoiding the costs of custom
programming. The control system shows much more
economical and efficient than the former FUNAC system.

origin point on the machine. It is difficult to reduce thepositioning repeatability error . The problem is to beAC

3. The modularized software
The software of the measurement system has beendeveloped into a modularized package which summarizes

B

ready forD

mappinrotatindatasystem
Fig. 3 The principle of setting absolute fiducial point

set excit

continuously

readily solved by establishing an absolute fiducial point bysoftware. The principle is shown in figure 3.
First, fix a reference switch on the bed of the mapping
machine and a knock block on the slide carriage to on/off
the switch at A point both in x and z axis individually.
When the slide moves along, the knock block knocks theswitch, computer gets a signal and asks the slide to stop at
C point, then asks it to return. After receiving the switch
signal at B point, the computer waits the first index pulse
comes from the encoder. No sooner had the computer got
the signal than it stopped sending motion instruction to themachine immediately. Finally the slide is driven to stop at
D point exactly. The D point is just the absolute fiducial
point precisely. The principle hasn’t theoretical error.

linear

4.2 Elimination of the backlash error

read DCCTNOKAxis selectionmovement
manua

auto
seek

go to measurement start

linear + arc

Adetermine parameters
total measurement lentgh
step distancespeed of motion
stop time for data accessnumber of measuring lines
use laser ?

read Hall probe

index

BCY
read

browse data fileNsatisfy ?
measurement
Fig. 2 sketch of the control program for mapping
measurement

movement control of the detectors, data acquisition anddata analysis together. The sketch of the control module formapping measurement is shown in Fig.2.
4 Improvement of positioning accuracy by software
4.1 Creation of the absolute origin point
As the control mode is semi-closed, there is no absolute

Omeasurement direction

Fig. 4Elimination of the backlash

The backlash between the shaft and nut or in shaft
coupling ,as an irregular factor, brings an extra error to thepositioning accuracy. A special program has beendeveloped to eliminate the error. Figure 4 is the procedure.
5 Introduction of the laser measurement device
The mechanical characteristic of the mapping machine
has determined the positioning accuracy within± 0.01mm. It lacks enough high position resolution for thedetailed investigation of the undulator whose nonhomogeneity is as high as 2 Gauss/0.01mm, which would
bring a big error to the first integral and the second integralof the magnetic field. The system’s flexibility allows us
to introduce a distance measurement device of highresolution to perform the special task conveniently. A laser

Measured field(Gauss)

6000

from ± 282 Gauss⋅ cm to ± 100 Gauss⋅ cm and thesecond integral has been changed from ± 24383 Gauss⋅
cm2 to ± 8000 Gauss⋅ cm2.

G ap = 40m m

4000
2000
06 Conclusion-2 0 0 0-4 0 0 00500

1000

15002000

P o s itio n a lo n g u n d u la to r

(m m )

2500

F ig . 5 M e as u re d f ield o f th e u n d u la to r

dual-frequency interferometer of resolution of 0.0001mm
has been added and well used for the undulator. The figure
5 is the measured magnetic field of the undulator.
After shimming, the performance of the undulator has
been greatly corrected. The first integral has been reduced

Application of IPC and upcoming modularized products
based on IPC to the magnetic measurement control system
has got an universal integrated facility. The system is formeasuring field of dipole, multipole, undulator and othermagnets. The characteristics of high reliability , openended design, convenience of operation, economy andefficiency aren’t well matched by the system composed of
dedicated micro computer or commercial computer.
Reference
1.The application to NC with Personal Computer,
NIKKEI, MECHANICAL, 1995, 6, 12, no.456, p38.