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James N. Bellinger

University of Wisconsin-Madison

25-February-2011

Z-sensor NewsZ-sensor News

James N. Bellinger 25-February-2011

Good n

ews th

is tim

e!

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What is the problem with Zsensors?

• Z sensor distances did not add up– Simple calculation, compare with calibration, all looks

OK– Review of CAD drawings, no smoking gun– LOW PRIORITY, little effort available

• Start with MAB positions and work outwards– Z positions of transfer plates don’t agree with PG

measurements

• Start with PG positions of ME4 and work in toward MAB– disagreements with MAB predictions of O(cm)

James N. Bellinger 25-Feb-2011

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Obvious check

• Take a ruler, measure the distances and compare with sensor readings– Can’t do it with field on, other tasks have priority

when field is off

• Xiaofeng measured these on Transfer Line 2 in January

James N. Bellinger 25-Feb-2011

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Z sensor Layout on Plate

James N. Bellinger 25-Feb-2011

2 plunger Z-sensors are mounted symmetrically on a mounting box, which is pinned to the transfer plate.

When disks are assembled, the Z-tubes push in on the plungers

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What was measured

James N. Bellinger 25-Feb-2011

Distance from face to box edge measured by Xiaofeng using a ruler. Error O(.5mm) ?

CAD coordinates

24.25 mm edge

-17.73 mm reference

I can treat both measurements the same way since the assembly is symmetric

Tube Face = Ref + Zsensor = Edge+Zruler ⇛Reference position ≈24.25+ Zruler – ZsensorExpect -17.73

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Explanation of Plots• I map both Z2 and Z1 calculations onto the

same place in the picture: Always using• 24.25 + XiaofengMeasurement – Zsensor• The standard Z-sensor measurement

calculation (relative to the reference point) is– Z(mm) = 10 (V-offset)/scale

• Motivated by Xiaofeng vs Zsensor plots (not shown) I tried– Z(mm) = 10 (-V-offset)/scale

• These are Normalized slope and offset

James N. Bellinger 25-Feb-2011

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Predicted reference position using standard formula

James N. Bellinger 25-Feb-2011

Z(mm)=10*(voltage-offset)/scale

Wide spread of values in the wrong place

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Predicted reference position using modified formula

James N. Bellinger 25-Feb-2011

Z(mm)=10*(-voltage-offset)/scale

Tight spread of values where they should be

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Conclusion• From the facts that

– The reference prediction is now where it ought to be; at the back of the Z-sensor

– The rms of the prediction is of the order of ruler measurement error rather than >2mm

• I think we can conclude that the sign on the voltage term in the Z calculation formula is wrong– Use Z=10*(-V-offset)/scale

• IR sensor was not tested here

• Thank you Xiaofeng!

James N. Bellinger 25-Feb-2011