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[James H Thomas <jhthomas AT berkeley.edu>]

Dear Richard at al.,

Using an assumption that the padplane is flat and the z coordinate is not important (ie Z == 0), then 5 coordinates (not 3) are required to describe the location of pads on a commercially manufactured padplane.   The extra two degrees of freedom are stretchX and stretchY due to the manufacturing process that puts a hot padplane through a pair of rollers to compress, fuse and flatten the final product.   

Typical numbers for the iTPC padplanes are:

ScaleX = StretchX, etc.

The table refers to deviations from the ideal pad locations.  The scale factors (stretch) are measured relative to an arbitrary (0,0) near the center of the padplane.  Note that the deltas and even the stretch factors can be positive or negative.    Using these extra degrees of freedom to represent the stretch in X and stretch in Y, the average pad position has a sigma of < 10 microns relative to the ideal position after suitable rotation and stretch.   This is a pretty amazing tolerance given that the scale of each padplane during manufacture is ~ 1 meter.

Cheers,

Jim

--

Jim Thomas

Email: jhthomas AT berkeley.edu

Phone:  USA  (510) 759-4936

Homepage: https://sites.google.com/berkeley.edu/jhthomas

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On Thu, Sep 21, 2023 at 12:30 PM Richard Witt via Star-tpc-l <star-tpc-l AT lists.bnl.gov> wrote:

Present: Alexei, Flemming, Jim, Tommy, Gene, and myself

== Hardware

— working on west laser

— PCB board was changed but didn’t work properly

— can use board with external relay (but relay failed)

— have driver to run UV crystal

— will finish alignment this week

== Electronics

— Tim going through list from Tonko

— a couple power cables have been fixed

— still many fuses on FEEs that must be fixed

== Software

— continuing to meet with Richard to work on SC calibrations ‘

— Run 21 FXT dE/dx calibration is done

— see https://drupal.star.bnl.gov/STAR/blog/fisyak/Runs-XXI-fixed-Target-dEdx-calibration-has-been-done

== AOB

— Jim’s thoughts on sector alignment to beamline

— used to assume the sectors were solid body rigid objects

— actually need 5 parameters, 2 additional to account for stretches of pad plane

— for iTPC, Jim accounted for all 5

— perhaps we should be doing the same 5 parameter procedure for alignment work?

— allow stretching for old outer sectors as well

Best Regards,

  Richard

Sent from my iPad

-- 
"Education is the most powerful weapon which you can use to change
the world."

--Nelson Mandela

~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~
 Richard Witt, Professor of Physics     Phone (USNA): 410-293-6675
    United States Naval Academy         Email: witt AT usna.edu
~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~

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