DEVELOPMENT OF A SINGLE CHANNEL MEASUREMENT SYSTEM
FOR MEASURING INSTANTANEOUS RADIAL MOVEMENTS OF INDUS-2
DIPOLE VACUUM CHAMBERS.
Prateek Bhatnagar, R.S.Yadav, Sujata Joshi, R. Sridhar, A.C.Thakurta#UHVTS
Raja Ramanna Centre For Advanced Technology, Indore, INDIA
Abstract
A measurement system has been designed and developed
for measuring the instantaneous miniscule radial
movements of Dipole vacuum Chambers of Indus-2
which are subjected to huge Lorentz force generated due
to the unusual situations of tripping of Dipole magnet
Power supply. The chamber movements were identified
as one of the sources of closed orbit drifts.
A small size linear motion potentiometer made of
conductive plastic resistance element is used as a
transducer. The change in resistance input due to change
in position of movement surface is interfaced to Isolated
Potentiometer Input module which provides a filtered,
isolated, amplified high level analog voltage output.
A Prototype measurement system was installed at the
entry side bellow of DP03 (Dipole Chamber 03) during
August, 2012 and the measurements were done for
various Beam filling conditions of Indus-2 machine. In
this paper we present the details of the measurement
system its testing, calibration and validation techniques.
INTRODUCTION
Indus-2, a 2.5 GeV machine, consists of eight super
periods, has 16 Aluminium alloy Dipole vacuum
chambers which are placed inside the 50 mm pole gap of
Dipole magnets. In unusual tripping of Dipole magnet
power supply the current of the magnets fall rapidly
thereby subjecting a huge Lorentz force on the Dipole
vacuum chambers. As a result there is a rapid
instantaneous radial movement of the Dipole vacuum
chambers from their mean position. In order to measure
the instantaneous radial movements of these chambers a
single channel measurement system has been developed
which provide continuous online data during various
beam filling conditions of Indus-2.
SYSTEM DESCRIPTION
As a good compromise between cost, sensitivity and
ease of installation a small size, 5KΩ, 25mm stroke
length, linear motion Potentiometer [1] made of
conductive plastic resistance element is chosen as basic
sensor having excellent linearity. The case material is
made of anodized Aluminium with end flanges made of
nylon & glass which are unaffected in magnetic field. The
shaft diameter of 5 mm has an easy feasibility of
clamping it to moving surface by M5 screws. The
transducer uses precious metal wipers to further enhance
reliability. Linear motion potentiometer made with
conductive plastic element had an edge over other
transducer as the measurements were very near to fringe
fields of 1.5 T Dipole magnets. The change in resistance
input due to change in position of movement surface is
interfaced to Isolated Potentiometer Input conditioner
module from ‘Dataforth’ [2], which provides a filtered,
isolated, amplified and converted to high level analog
voltage output. The conditioner has a very good accuracy
viz. +/- 0.03% span (Typical), Linearity +/- 0.03% span
(Typical) and frequency response. The selected module
has an input range of 0 to 5KΩ and Output Range of 1 to
+5V. In order to preserve the integrity of the voltage
signal in high EMI and RFI environment, the voltage
signal is interfaced with a signal conditioning module
converter which converts it to 4-20 mA range for further
acquisition and Data display at control room.
The complete system consisting of a conditioner,
converter and 24 Volts power supply are mounted on DIN
rails very near to the basic sensor, which is connected
near the beam entry side of Dipole vacuum chamber on
thin walled RF shielded bellow. The mounting of sensor
was on a rigid stand which could fulfil the basic
requirements viz. stability and working in fringe magnetic
field of quadrupole and dipole magnets. The stand,
grouted on the ground, was designed of completely non
magnetic SS 316 plates.
Transfer Function, Lab testing & calibration of
the system
The change in displacement and change in current holds a
relationship as
∆ X Input (µm) α ∆ I output (µA)
The mathematical relationship between the ∆I output (µA)
and ∆X Input (µm) fits into the linear equation of
∆ X Input (µm) = 1.56 (µm/ µA). ∆ I output (µA)
Where,
∆I output (µA) = Change in analog value of current output
from signal conditioning module.
∆X Input (µm)= Change in Displacement input of the
conductive plastic Linear Potentiometer governed by a
sensitivity factor of 20Ω/100µm, assuming the
relationship to be linear within specified temperature of
Indus-2 tunnel (25+/-1 °C) .
The factor 1.56 has been calculated by multiplying the
gains of the three subsystems of the system.
Let I output1 (initial (µA)) be the initial value of I, corresponding
to initial home position X Input1 (initial (µm)) when the sensor
is mounted at a certain initial home position on the entry
side RF shielded bellow.
Consequent to dynamic displacement let new values be
I output2 (initial2 (µA)) and X Input2 (initial2 (µm))
Mathematically,
X Input1 (initial (µm)) = 1.56. I output 1(initial (µA)) at time T=0
X Input2 (initial (µm)) = 1.56. I output 2(initial (µA)) at time T=T1
Thus,
∆ X Input (µm) = 1.56(µm/ µA). ∆ I output (µA)
Where,
∆ X Input (µm) = X Input2 (initial (µm)) - X Input1 (initial (µm)),
∆ I output (µA) = I output 1(initial (µA)) - I output 2(initial (µA))
Table 1: Radial movement (Positional) of Dipole chamber
03 during filling of Indus-2 Beam current
Validation of the Linear equation was carried out for two
independent assembled systems at the Computerised
CMM (Coordinate measurement machine) , capable of
precise positioning of the sensor spindle, by giving fixed
sets of increment and decrement displacement of 100
microns to the Linear potentiometer which was doubly
verified by a high resolution Micrometer Dial gauge.
Time
7:30:00
8:00:00
8:30:00
9:00:00
9:30:00
10:00:00
10:30:00
11:00:00
Beam
current
(mA)
0
0
55.73
109
107
103
98.68
94.29
Beam
energy
(GeV)
0
0
550
550
2480
2500
2500
2500
11:30:00
12:00:00
12:30:00
13:00:00
89.88
85.27
82.22
78.79
2500
2500
2500
2500
Beam Current(mA)
Output current(mA)
8.05
8
7.95
7.9
7.85
7.8
7.75
7.7
7.65
7.6
7.55
7.5
7.45
7.4
7.35
7.3
12.115
12.128
12.2
12.258
∆I
(µA)
∆X
(µm)
X
(µm)
101
183
250
-95
-163
145
157
286
390
-148
-254
226
157
443
833
685
431
657
335
13
72
58
523
20
112
90
1180
1200
1312
1402
Instantaneous radial movements of Dipole Chamber no.3 (DP03) w.r.t.
Beam current
120
Graph between Displacement of Linear
Potentiometer and current output carried
out on CMM
Measured
current
(mA)
11.356
11.359
11.46
11.643
11.893
11.798
11.635
11.78
100
3000
Beam current
Beam energy
X (µm) 2500
80
2000
60
1500
40
1000
20
500
0
Series1
0
7:30 8:00 8:30 9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00
Series2
Figure 2: Graph showing Instantaneous radial
movements of Dipole chamber 03 (DP03) w.r.t to Indus-2
beam current.
Linear Displacement (microns)
0
100 200 300 400 500 600 700 800 900 1000 1100
Figure 1: Calibration graph between displacement of
linear potentiometer and current output carried out on
CMM.
MEASUREMENT AND RESULTS
A rigid support stand was designed by the mechanical
group looking to the point of view of ease of installation,
long term stability and availability of space. The sensor
was mounted on the stand and the end of the shaft was
connected via extension rod on the entry side bellow of
Dipole chamber no. 3 (DP03) [3].The change in current
output was brought out of tunnel via twisted pair of signal
cables. The current values were measured on a
‘Yokogawa’ make ‘CA71’ calibrator.
Figure 2 shows the graph between measured
instantaneous radial movement of the dipole chamber 03
w.r.t. Indus-2 beam current
Figure 3: Measurement system installed at Dipole
chamber no. 3 (DP03) at Indus-2 tunnel.
CONCLUSION
An inexpensive and accurate measurement system was
installed at the entry side of DP03 (Dipole Chamber 03)
of Indus-2 which gave us confidence to prepare 16 Nos.
of similar systems so that they can be placed in similar
positions of Dipole chamber .The data on further analysis
shows that there exists a substantial radial instantaneous
movement of chamber during various beam filling
conditions, attributed due to various reasons, which can
be further be arrested by replacing the existing supports
by the ones from the ground.[4][5]
The efforts are in progress to procure a suitable a high
speed Data acquisition system which can acquire these
datas for further display. Given these test results, current
plans are to re-measure both vertical and horizontal
movements at several locations with improved support
stands.
ACKNOWLEDGEMENT
The author appreciates useful technical discussions
with members of FOFB (Fast Orbit Feedback System).
Acknowledgements are due to Shri K K Malviya and Shri
C B Kulkarni, UHV for fabrication and installation of
support stands for the sensor. Our acknowledgements are
also due to Shri R S Shinde ,Shri Subrata Das,Shri
Kailash Ruwali ,Accelerator magnet Technology Division
for imparting the necessary help and infrastructure in
making use of the CMM machine.
REFERENCES
[1] Elap; Type Series PM 25; 5K
[2] DataForth; SCM7B 36-05
[3] G. Schmidt, U. Berges, J. Friedl, E. Kasel, K. Wille , D.
Zimoch, DELTA, University of Dortmund, Germany
“Position sensors for monitoring accelerator magnet
motion at Delta” Proceedings of EPAC 2002, Paris
[4] G. Schmidt et al; Position Monitoring of Accelerator
Components as Magnets and Beam Position Monitors,
DIPAC 2001,
[5] L. Solomon’, D. Lynch, BNL; J. Safranek, SSRL; 0. Singh,
ANL “Chamber motion measurements at the NSLS x-ray
ring”