PXL vibration and stability

1/7/2014

Measurements of:

• Cooling air induced vibration of the PXL sensors as a function of air flow

• DC position change as a function of air flow• Position change between power on, warm sector and

power off cold sector

Radial sector motion measured with capacitive probe inserted through hole in PST

North half sectors populated with operating ladders. South half populated with empty sector tubes. System operated with full cooling air

Probe position 1

Probe position 2

Sector 3, ladder position out3 Sector 3, ladder position out2

Probe faces the carbon tube flat just west of the ladders

Typical screen shot at full air flow

Probe signal

FFT, see next page for more detail

Stdev = 5 m

Probe conversion = 1 m/0.04 V

Fourier transform of sector vibration

40 Hz

70 Hz

230 HzMain resonance of the carbon sector tube

Measured sector radial vibration as a function cooling air flow for position 1

More precisely this shows measured vibration as a function of blower RPM since flow has been obtained in this case by scaling linearly with RPM. It has been shown, however, that the flow does indeed scale very closely to the blower RPM.

The measured vibration with no air flowing: 35 nm RMS

Radial displacement of the sector at position 1 as a function of vibration amplitude

An arbitrary offset has been applied to give a 0 intercept since a displacement value was not recorded at zero flow for this series of measurements.

The linear dependence demonstrates that the displacement like the vibration amplitude scales as the flow squared. This is not so surprising since the dynamic pressure scales as air velocity squared.

Sector displacement scales as cooling air flow squared.

Sector moves toward the center with increased flow.

Radial movement between power on and power off with full flow, i.e. Blower RPM = 5940

The sector end moves 3 to 8 m in toward the center when ladder power is applied.The temperature rise with power on is between 10 and 12 deg C depending where on the silicon one measures.

This is roughly what was predicted in the FEA analysis done in 2008, see p. 8 of:

http://www-rnc.lbl.gov/~wieman/beam-4%20load%20snout%20end-1.pdf

The end drops in this analysis 6 m for a 20 deg C temperature rise. This analysis demonstrated the need for a soft adhesive and reinforcement at the open end to achieve this limited displacement.

Summary

Sector vibration in the radial direction scales as: flow2

Sector vibration at full flow: 5 µm RMS

Sector DC displacement scales as: flow2

Sector moves in at full flow: 25 µm - 30 µm

Sector moves in when ladders powered: 3 µm - 8 µm

Sources:OneNote logbook: work>sector vibration>Vibration test full with MSCAnalysis: As>AHFT1>cHFT>m>vibration wind>vibration measured full detector.xmcd