Wire tension meter for LHCb’s Outer tracker – reliability tests

G. Apeldoorn, T.Bauer, J. Nardulli, A. Pellegrino, T. Sluijk, P. Vankov

LHCb-week, Zurich, September 15-19, 2003

The tool

P. Vankov LHCb-week, September 2003, Zurich

Five Wire Tension Meters (WTM) are produced

- NIKHEF design

- realized in an external company (“Engineering spirt”)

WTM measures the oscillation frequency (f) or period (T) of the wire in presence of magnetic field

- Range (0 – 300 Hz)

- RS-232 connection

If f is equal to the wire’s fundamental oscillation frequency (the first harmonic), then the wire tension (F [gr]) is:

,where: r – the radius of the wire, [cm],

L – the length of the wire, [cm],

ρ – the density of the wire, [gr/cm^3],

g – the earth acceleration, [cm/ms^2].

Principle of the operation of the WTM

P. Vankov LHCb-week, September 2003, Zurich

1. An initial short (0.8 ms) current pulse (I ~130mA ) is sent (by the WTM) through the wire (placed in a perpendicular magnetic field B~0.05T)

2. The Lorentz force causes a mechanical oscillation of the wire

3. The vibrations are in a magnetic field => induction of an emf ε ~ cos(ωt)

4. The WTM scans ε and defines ω=2πf, f=ω/2π

5. To assure oscillation with the fundamental frequency, the magnetic field B should be localized in the middle of the wire.

In our case (LHCb straw tubes wire):

r = (0.001/2)inch = (0.00254/2)cm = (25.4/2)μm

ρ = 19.253 gr/cm^3

g = 0.000980665 cm/ms^2

The wire tension expressed in grams:

,as: L=L [cm], f=f [Hz], T=T [ms]

The experimental setups

P. Vankov LHCb-week, September 2003, Zurich

Two experimental setups were created to test the reliability of the WTM:

1. Horizontal setup 2. Vertical setup

In both of them is possible to be changed the length of the wire and the nominal weight, which produces the tension.

Results (horizontal setup)

P. Vankov LHCb-week, September 2003, Zurich

Measurement of T [ms] for different nominal weights, when L is fixed to 102cm.

For each nominal weight are taken 50 measurements. The wire tension is calculated:

The measured value of the tension is ~ 1.0 % lower than the nominal one.

The data from Wtm#2 and Wtm#3 are compatible within ~ 1 ‰.

Wtm#2,L=102cm

Wtm#3,L=102cm

Results (horizontal setup)

P. Vankov LHCb-week, September 2003, Zurich

From the straight-line fit:

Which means that L must be:

From where:

L=102.4cm(Wtm#2)

L=102.5cm(Wtm#3),

But the nominal length is

Ln =102.0cm, and:

(L/Ln)% = 0.4-0.5 %

Wtm#2,L=102cm

Wtm#3, L=102cm

Results (horizontal setup)

P. Vankov LHCb-week, September 2003, Zurich

Measurement of T [ms] for different lengths (L), when the nominal weight is fixed to 140gr (or 70gr-expected value of the wire tension).

For each L are taken 50 measurements. The wire tension is calculated:

The measured value of the tension is ~ 1.0-1.1 % lower than the nominal one.

Wtm#2,70gr

Wtm#3,70gr

Results (horizontal setup)

P. Vankov LHCb-week, September 2003, Zurich

Wtm#2,70gr

Wtm#3,70gr

F=68.4gr (Wtm#2)

F=69.6gr (Wtm#3)

F nominal=70gr.

(F/F nominal)% = 0.6-2.2 %

Results (vertical setup)

P. Vankov LHCb-week, September 2003, Zurich

F nominal = 57.8gr

(F/F nominal)% = ~ 0.3-0.4 %

Wtm#3

Fn=57.8gr,L=53cm

Results (vertical setup)

P. Vankov LHCb-week, September 2003, Zurich

Fn=67.8gr,L=53cm

Fn=77.9gr, L=53cm

(F/F nominal)% = ~ 0.2 % (F/F nominal)% = ~ 0.5 %

Summary

P. Vankov LHCb-week, September 2003, Zurich

The horizontal setup gives (F/F nominal)% ~1.1% The vertical setup gives (F/F nominal)% ~ 0.5%

This difference could be explained with the friction forces between wire and the locators, and wire and the pulleys, acting when is used the horizontal setup.

Since the vertical setup is the most simplified one, is possible to be concluded that

the precision of the WTMeter for the LHCb Outer tracker straw tubes is ~ 0.5%.