Description: Fig.2 , Filename: ch3.ps
WIRE TENSION MEASUREMENT
Yu.Davydov, W.Faszer
Two wire planes of PPP (identified as plane #2 and plane #3) were
strung and the tension of each wire has been measured.
KFKI wire stretch meter was used to check wire tensions. The meter
measures wire tensions based on determining the wire oscillation period in a
magnetic field. For a known oscillation period T one can calculate the
stretching force F:
F=pi*rho*l**2d**2/T**2
where rho, l and d are density, length and diameter of the wire.
All sense wires have diameter 15mkm (gold plated W), three guard wires
- 30 mkm (gold plated W), 50 mkm (Cu-Be) and 75 mkm (Cu-Be). The length of each
wire is defined by two spots of glue which fix that wire at each end to the
glass frame. Follow expression was used to calculate the length of each wire:
l=2*sqrt{R**2-[4(n-1)-170]**2 } ;
where n is wire number and R is radius on which wires are fixed with glue. R is
defined by radius of inner hole of glass frame plus 1-2 mm (we do not know a
way of accurately positioning the glue spots yet). The diameter of the glass
frame hole is 392 mm in plane #2 and 393 mm in plane #3. So we have used
R=198 mm to calculate length of wires for both planes.
Sense wires were stretched with a 35g weight, guard wires with 60g, 80g
and 125g weights. Results of calculated wire tensions based on the measured
period oscillation of each wire for planes #2 and #3 are shown on the fig.1
and fig.2 (only sense wires are included in the tension distributions). We
found wire tension to be about 15g less than the applied weight. Our quick
test showed that this is caused by high friction of the wire on the surfaces
of steel screw and glass ruler. Some wires on the plane #3 have tension of
about 30g. This happened due to lifting these wires from the surfaces of the
glass ruler and steel screw on the one end to reposition them while the weight
was applied which overcame the friction.
Calculated stretching force F depends on wire length. Figure 3 shows
the effect of inaccurate knowledge of wire length on the stretching force.
Tension distributions for plane #2 for three different values R are shown
(solid line for R=198mm, dashed line for R=197mm and dotted line for R=199mm).
1mm mistake on R gives 2mm mistakes of length on central wires and about 4mm
for short wires. It seems we have to measure length of each wire after winding
in order to decrease that effect. We can provide precision of that measurement
to about (+/-0.5 ... +/-1)mm which should be enough for our purposes.
Description: Fig.1 , Filename: ch2.ps
Description: Fig.2 , Filename: ch3.ps
Description: Fig.3 , Filename: ch2_l.ps