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Tension control device for wires in large multiwire proportional chambers
NUCLEAR INSTRUMENTS AND METHODS 153 ( 1 9 7 8 )
379-381
: O
N O R T I t - t l O L L A N D P U B L I S I t l N G CO.
TENSION C O N T R O L DEVICE FOR WIRES IN LARGE M U L T I W I R E P R O P O R T I O N A L CHAMBERS* ALESSANDRO BORGIIESI
lstituto di Fisica Generale "A. Volta ", Universit(~ di Pavia, 27100 Pavia, Italy Received 29 December 1977 A detailed description is reported on wire tension method and wire tension control for the large multiwire proportional chambers (2.6×1.3m 2) used at the SPEAR I e + e storage ring.
The wire tensioning and the tension control systems are two of the most important problems to be solved in the construction of large dimension proportional wire chambers, with a large n u m b e r of wires per plane. To build 5 M W P C for an experiment to study inclusive hadron production in the e - e - annihilation at 5 GeV c.m.s, at SPEAR I, Stanford e ' e storage ring~), a total of 3300 wires were assembled. The stretching m e t h o d and the tension control systems required particular care and the solution of some new technical problems. In the following we describe in detail the instrumentation, its construction methods and the resuits of its performance. The wires were winded on a winding machine 2) with a mechanical tension as uniform as possible and much lower than the final wire tension in the MWPC. The wires were then epoxied to two parallel a l u m i n u m bars and transferred from the winding machine to a stretching table 3) without releasing their mechanical tension. On the stretching table the wire tension was encreased to the nominal value of 60 g per wire and the control of the absolute value of the tension of all wires was performed collectively. Such collective control m e t h o d was based on the m e a s u r e m e n t of the fundamental natural frequency of oscillation of the stretched wires. This frequency is given by T = 412Apv 2, where T is the stretching force, l is the wire length, A is the cross-section area of the wires and p is the linear density o f the wires. So we can obtain the fundamental oscillation frequency v of the wires for the desired wire tension. * This work was supported by Istituto Nazionale di Fisica Nucleare, Sezione di Pavia.
In fig. 1 the behaviour of the fundamental oscillation period versus the mechanical tension for a wire 255 cm long is shown. As can be seen from this figure a high resolution in T can be obtained due to the relation between the mechanical wire tension and the resonance frequency. The oscillation of the wire was induced exciting the stretched wire plane which was capacitively coupled with a high voltage oscillator. This capacitive coupling was obtained with an a l u m i n u m bar placed 10 cm from the wire plane and perpendicularly to the wires. In fig. 2 the block diagram of the device used to apply the excitation high voltage to the wires (-~ 5 kVcrr) is shown. At an excitation frequency of one-half the fundamental mechanical vibration 70
60 [.50
40
30
A
20
,o
-A 5
I
t
I
20
30
40
50 ms
Fig. 1. Mechanical wire tension T as a function o f the induced stationary oscillation period. The curve is shown for a wire length o f 255 cm. The period on the abscissa is for the resonance oscillation.
380
a. BORGHESI
frequency of the wire, a stationary wave was clearly visible with a m a x i m u m amplitude at the resonance
t ov pec
YR = ~ - ~ --
y=o'
where / is the wire length, T is the mechanical wire tension, C is the capacity of the wire alumin u m bar system, Q is the factor of merit (about 40) and V~,p is the peak-to-peak excitation voltage. In fig. 3 can be seen the behaviour of the relative oscillation amplitude YlYR vs the stretching force: the Y/YR value was determined by a stroboscope which allowed also the control of the uniformity of the whole wire plane tension. As shown ill fig. 3, a 209,3 variation of the m a x i m u m oscillation amplitude (easily observed with the stroboscopic technique), gives a tension force accuracy lower than + 1 g. After the wire stretching and the tension control of the wires with the collective m e t h o d described above, the wires were glued on the frame. T h e n the assembled frame was submitted to a final uniformity control in which the mechanical tension of each wire was measured individually.
The mechanical tension value of each wire was obtained measuring the sagitta caused by a freefalling known weight on the center of the wire. The relation between sagitta y, weight p, wire length / and tension T is (in the small displacements approximation)
y-
pl 4T"
The sagitta was measured with a position transducer based on a differential transformer with a freefalling iron-silicon cilindrical core. The core was hollow (0.2 m m thick), to minimize its weight and its bottom end (fig. 4a) was connected to a non ferromagnetic cilindric stick. This stick, in contact with the wire, prevented the core to get out from the magnetic field and allowed the linear performance of the transducer. With such device and feeding the differential transformer with a power amplifier driven by a
ectromagnet
oscillator
Fig. 2. Block diagram of the apparatus used for the resonance m e a s u r e m e n t on the wires.
differenti transduc
781t!.......... 'i
t free-falling probe
a)
b) to DVM
>~.6 /
.sk
56
58
60
62
64
T(g) Fig. 3. Relative oscillation amplitude for a wire vs the mechanical tension lm long.
tranducer ~x ~,
~_ __Lcable tray ~ ,--~ slides
/
reference plane endless-screw Fig. 4. a) Position transducer and lifting system used for mechanical wire tension measurements; b) particular of the falling probe of the position transducer; c) schematic plan view of the single wire control device.
TENSION
0.35
v
>
CONTROL
. . . . . .
0.30
1
°25i
4
0.20 0.15
I
l
1
2
3
4
5
,
6
sagitta(mm) Fig 5. Calibration curve of the position transducer. very stable oscillator, a linear m o v e m e n t of 12 m m about was obtained. The total weight of the free-falling probe was 868 rag. The m e a s u r e m e n t of the induced differential voltage, proportional to the displacement of the probe in contact with the wire and hence to the sagitta, was performed with a digital voltmeter. T h e experimentally observed linear dependence between the sagitta and the induced differential voltage is s h o w n in fig. 5. Because of the large n u m b e r of wires a semiautomatic tension m e a s u r e m e n t for each wire was necessary. This was performed by a suitable device. T h e probe flowed in a glass capillary inserted in the transducer coil. T h e top of such capillary was fixed to a hollow ferromagnetic core. This s y s t e m (see fig. 4b) allowed to lift the core of the differential transformer with a n o t h e r electromagnet and to let it fall by gravity on the wire, with
DEVICE
FOR
WIRES
381
a gradual deexcitation (to prevent the wire surface from any damage) of the electromagnet. The whole device could m o v e parallelly to the wires on two rigid slides (see fig. 4c). Perpendicularly to the wires the m o v e m e n t was performed by an endless screw. In this way it was possible both a rapid calibration with respect to a reference plane and a speedy m e a s u r e m e n t of the sagitta. A microswitch automatically enabled to lift the probe from the wire before every transversal displacement of the apparatus and to lower the freefalling weight for the sagitta m e a s u r e m e n t . The s y s t e m gave a vary high resolution and an excellent repetition precision because the transducer was assembled practically without friction. In our case the resolution was about 1 ,urn and the sagitta distribution from m e a s u r e m e n t s made on a single wire gave a standard deviation of about 2/xm. The data taken from the chambers were analyzed and plotted by a c o m p u t e r ; the mechanical wire tensions measured individually were in agreem e n t within 1% with those taken by the collective methods. T h e standard deviation distribution of the mechanical tension turned out to be about 1.5g. It is a pleasure to t h a n k Dr. G. Bellodi and Prof. D. Scannicchio for the critical reading of the rnanuscript. References i) T. L. Atwood, B. A. Barnett, I,. V. Trasatti, O. T. Zorn, M. Cavalli-Sfl)rza, (.E Goggi, G. C. Mantovani. A. Piazzoli, B. Rossini. D. Scannicchio, l). G, Coyne, G. K. O'Neill and tl. l". W. Sadrozinski, Plays. Rex.. Left. 35 (1975) 704. 2) K. B. Burns. B. R. Brummon, T. A. Numaker. I,. W. Mo and S. C. Wright. E. Fermi Institute, Chk:ago, Internal Report 72/37. 3) M. Cavalli-Sforza. O. Goggi, A. Piazzoli, B. Rossini and D. Scannicchio, Nucl. Instr. and Meth. 124 (1975) 73.
379-381
: O
N O R T I t - t l O L L A N D P U B L I S I t l N G CO.
TENSION C O N T R O L DEVICE FOR WIRES IN LARGE M U L T I W I R E P R O P O R T I O N A L CHAMBERS* ALESSANDRO BORGIIESI
lstituto di Fisica Generale "A. Volta ", Universit(~ di Pavia, 27100 Pavia, Italy Received 29 December 1977 A detailed description is reported on wire tension method and wire tension control for the large multiwire proportional chambers (2.6×1.3m 2) used at the SPEAR I e + e storage ring.
The wire tensioning and the tension control systems are two of the most important problems to be solved in the construction of large dimension proportional wire chambers, with a large n u m b e r of wires per plane. To build 5 M W P C for an experiment to study inclusive hadron production in the e - e - annihilation at 5 GeV c.m.s, at SPEAR I, Stanford e ' e storage ring~), a total of 3300 wires were assembled. The stretching m e t h o d and the tension control systems required particular care and the solution of some new technical problems. In the following we describe in detail the instrumentation, its construction methods and the resuits of its performance. The wires were winded on a winding machine 2) with a mechanical tension as uniform as possible and much lower than the final wire tension in the MWPC. The wires were then epoxied to two parallel a l u m i n u m bars and transferred from the winding machine to a stretching table 3) without releasing their mechanical tension. On the stretching table the wire tension was encreased to the nominal value of 60 g per wire and the control of the absolute value of the tension of all wires was performed collectively. Such collective control m e t h o d was based on the m e a s u r e m e n t of the fundamental natural frequency of oscillation of the stretched wires. This frequency is given by T = 412Apv 2, where T is the stretching force, l is the wire length, A is the cross-section area of the wires and p is the linear density o f the wires. So we can obtain the fundamental oscillation frequency v of the wires for the desired wire tension. * This work was supported by Istituto Nazionale di Fisica Nucleare, Sezione di Pavia.
In fig. 1 the behaviour of the fundamental oscillation period versus the mechanical tension for a wire 255 cm long is shown. As can be seen from this figure a high resolution in T can be obtained due to the relation between the mechanical wire tension and the resonance frequency. The oscillation of the wire was induced exciting the stretched wire plane which was capacitively coupled with a high voltage oscillator. This capacitive coupling was obtained with an a l u m i n u m bar placed 10 cm from the wire plane and perpendicularly to the wires. In fig. 2 the block diagram of the device used to apply the excitation high voltage to the wires (-~ 5 kVcrr) is shown. At an excitation frequency of one-half the fundamental mechanical vibration 70
60 [.50
40
30
A
20
,o
-A 5
I
t
I
20
30
40
50 ms
Fig. 1. Mechanical wire tension T as a function o f the induced stationary oscillation period. The curve is shown for a wire length o f 255 cm. The period on the abscissa is for the resonance oscillation.
380
a. BORGHESI
frequency of the wire, a stationary wave was clearly visible with a m a x i m u m amplitude at the resonance
t ov pec
YR = ~ - ~ --
y=o'
where / is the wire length, T is the mechanical wire tension, C is the capacity of the wire alumin u m bar system, Q is the factor of merit (about 40) and V~,p is the peak-to-peak excitation voltage. In fig. 3 can be seen the behaviour of the relative oscillation amplitude YlYR vs the stretching force: the Y/YR value was determined by a stroboscope which allowed also the control of the uniformity of the whole wire plane tension. As shown ill fig. 3, a 209,3 variation of the m a x i m u m oscillation amplitude (easily observed with the stroboscopic technique), gives a tension force accuracy lower than + 1 g. After the wire stretching and the tension control of the wires with the collective m e t h o d described above, the wires were glued on the frame. T h e n the assembled frame was submitted to a final uniformity control in which the mechanical tension of each wire was measured individually.
The mechanical tension value of each wire was obtained measuring the sagitta caused by a freefalling known weight on the center of the wire. The relation between sagitta y, weight p, wire length / and tension T is (in the small displacements approximation)
y-
pl 4T"
The sagitta was measured with a position transducer based on a differential transformer with a freefalling iron-silicon cilindrical core. The core was hollow (0.2 m m thick), to minimize its weight and its bottom end (fig. 4a) was connected to a non ferromagnetic cilindric stick. This stick, in contact with the wire, prevented the core to get out from the magnetic field and allowed the linear performance of the transducer. With such device and feeding the differential transformer with a power amplifier driven by a
ectromagnet
oscillator
Fig. 2. Block diagram of the apparatus used for the resonance m e a s u r e m e n t on the wires.
differenti transduc
781t!.......... 'i
t free-falling probe
a)
b) to DVM
>~.6 /
.sk
56
58
60
62
64
T(g) Fig. 3. Relative oscillation amplitude for a wire vs the mechanical tension lm long.
tranducer ~x ~,
~_ __Lcable tray ~ ,--~ slides
/
reference plane endless-screw Fig. 4. a) Position transducer and lifting system used for mechanical wire tension measurements; b) particular of the falling probe of the position transducer; c) schematic plan view of the single wire control device.
TENSION
0.35
v
>
CONTROL
. . . . . .
0.30
1
°25i
4
0.20 0.15
I
l
1
2
3
4
5
,
6
sagitta(mm) Fig 5. Calibration curve of the position transducer. very stable oscillator, a linear m o v e m e n t of 12 m m about was obtained. The total weight of the free-falling probe was 868 rag. The m e a s u r e m e n t of the induced differential voltage, proportional to the displacement of the probe in contact with the wire and hence to the sagitta, was performed with a digital voltmeter. T h e experimentally observed linear dependence between the sagitta and the induced differential voltage is s h o w n in fig. 5. Because of the large n u m b e r of wires a semiautomatic tension m e a s u r e m e n t for each wire was necessary. This was performed by a suitable device. T h e probe flowed in a glass capillary inserted in the transducer coil. T h e top of such capillary was fixed to a hollow ferromagnetic core. This s y s t e m (see fig. 4b) allowed to lift the core of the differential transformer with a n o t h e r electromagnet and to let it fall by gravity on the wire, with
DEVICE
FOR
WIRES
381
a gradual deexcitation (to prevent the wire surface from any damage) of the electromagnet. The whole device could m o v e parallelly to the wires on two rigid slides (see fig. 4c). Perpendicularly to the wires the m o v e m e n t was performed by an endless screw. In this way it was possible both a rapid calibration with respect to a reference plane and a speedy m e a s u r e m e n t of the sagitta. A microswitch automatically enabled to lift the probe from the wire before every transversal displacement of the apparatus and to lower the freefalling weight for the sagitta m e a s u r e m e n t . The s y s t e m gave a vary high resolution and an excellent repetition precision because the transducer was assembled practically without friction. In our case the resolution was about 1 ,urn and the sagitta distribution from m e a s u r e m e n t s made on a single wire gave a standard deviation of about 2/xm. The data taken from the chambers were analyzed and plotted by a c o m p u t e r ; the mechanical wire tensions measured individually were in agreem e n t within 1% with those taken by the collective methods. T h e standard deviation distribution of the mechanical tension turned out to be about 1.5g. It is a pleasure to t h a n k Dr. G. Bellodi and Prof. D. Scannicchio for the critical reading of the rnanuscript. References i) T. L. Atwood, B. A. Barnett, I,. V. Trasatti, O. T. Zorn, M. Cavalli-Sfl)rza, (.E Goggi, G. C. Mantovani. A. Piazzoli, B. Rossini. D. Scannicchio, l). G, Coyne, G. K. O'Neill and tl. l". W. Sadrozinski, Plays. Rex.. Left. 35 (1975) 704. 2) K. B. Burns. B. R. Brummon, T. A. Numaker. I,. W. Mo and S. C. Wright. E. Fermi Institute, Chk:ago, Internal Report 72/37. 3) M. Cavalli-Sforza. O. Goggi, A. Piazzoli, B. Rossini and D. Scannicchio, Nucl. Instr. and Meth. 124 (1975) 73.