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LED Holder Calibration for Barrel Muon Chambers - Method and Experience

This paper discusses the calibration of LED holders for barrel muon chambers, including the calibration tool design and measurement process. The reproducibility of the method and bench is also examined.

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LED Holder Calibration for Barrel Muon Chambers - Method and Experience

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  1. Calibration of the LED holders for Barrel Muon ChambersMethod, Experience Zoltán Szillási University of Debrecen, Institute of Experimental Physics, Debrecen, Hungary The work is supported by The Hungarian Scientific Research Fund OTKA T 026178, T034910, T 043145

  2. The forks on a chamber Chamber LED holders (forks) 003 004 minicrate Top view 002 001 001 – 004: specific code * • During the fork installation on the chamber the only important thing is • to put forks of four different specific codes. The sequence shown on the picture is the conventional one but the order is checked and memorised during the chamber calibration.

  3. Fork parts a) b) c) d) • Mechanics • LED • LED-PCB • Driver PCB

  4. Assembled fork a) LEDs mounted b) Fork assembled

  5. Fork mounted on the chamber a) b) c) Fork mounted a) Fork with the cover b) Fork in the passage c) d) Fork in operation d)

  6. The fork design Drawing for the workshop: Drawing to understand: LED-s shining in our direction (4LEDs) Positioning holes Positioning surface LED-s shining in the opposite direction (6 LEDs) 71 mm

  7. Aim of the fork-calibration The aim of the fork-calibration: to determine the LED positions with respect to the LED holder frame defined by the flat surface and the two pins on the chamber:

  8. camera Fork ~500 mm Fork LEDs (on both sides) Optical fibers (on both sides) Calibration tool Y-motion X-motion ~500 mm camera Calibration – principle The calibration tool (with light sources of known position) is sitting on a 2D precise motion table. The fork to be calibrated is attached to the tool. The table is moving until the light sources are appearing one by one in the same position on the video-camera. Traveling distances are recorded. Two sides are connected by the pre-calibration of the tool.

  9. LED holder calibration – tool design

  10. LED holder calibration bench in Debrecen a) b) c) d) • The bench (during the test) • The calibration tool with a LED holder • The calibration tool on the 2D table • d) The bench during operation (The LED-s on the holder are ON)

  11. The calibration setup - electronics Calibration table LEDs (Cal. Tool + fork) Left camera Right camera X-Y table X-Y table Temperature sensor INTERNET I2C Barcode reader TCP/IP RS232 Data server Measuring PC X-Y table driver

  12. The measurement: steps • Insertion of the fork in the tool • Reading of the barcode of the fork • Operator’s name (selection from the menu or new name) • Click on the “start” button • Automatic measurement. The full calibration tool and fork • (6 fibers and 10 LEDs) are measured 5 times. • Loading of raw data into the Database and EXIT. • Time needed for steps 1-5: 3 minutes • Time needed for step 5: 40 minutes The measurement program window:

  13. Software organization Measurement program: VISUAL C++ (Windows’98) Data Loader:JAVA Function: - Loading into the database for the given fork: the header (fork number, operator, date, time, temperature), the X-Y table positions for the spot found and its max. brightness. Database: MySQL (Linux) Analysis Tool: JAVA (Linux) Function: - Coordinate transformations - Preparation of the validity check of the measurement - Puts the data in the database - Sets the label “fork has been analyzed” Reporting Tool: Shell and MySQL scripts, HTML and ASCII output Function: - Checks the validity of the measurement - Takes the “good – not good” decision - Creates the output files - Updates the statistics Packing Tool:JAVA (Linux) Function: - Checks (from the barcode) if the fork has been measured, analyzed - Checks if the fork calibration is valid

  14. Rejection criteria Rejection of a measurement: The Analysis Tool is rejecting a measurement (from the 5 measurements taken) if for any fiber or LED: T-test result is negative (point with >2.75 sigma) AND the max-min value for the same fiber or LED is > 10 μm. Rejection of the calibration: The Reporting Tool (besides other tasks) is checking the goodness of the calibration. It is rejecting the calibration if: More than one measurement has been rejected (action: new calibration) OR for any LED the brightness is < 60% of the saturation (action: replacement of the LED and new calibration) Passed with warning: One measurement has been rejected OR for any fiber or LED: 60% < brightness < 80% OR for any LED the calibrated - design position > 75 micrometer

  15. Reproducibility of the method and the bench 1) Reproducibility of the spot-finding: max-min value < 4 μm in X (CMS-Phi) max-min value < 4 μm in Y (CMS-R) for both the fibers and LEDs. 2) Reproducibility of the fork calibration: The fork No. 351115000100020 has been calibrated 6 times (1x on 19 Dec 02 and 5x on 10 Jan 03). Both 1 and 2 are VERY GOOD!

  16. Status , Statistics Up to now (8 Apr 2003) 200 forks have been calibrated. 120 of them are already delivered to CERN. Finally all the forks calibrated so far “passed”, 22 of which with warning: • - 1 with “one measurement rejected” warning • 6 with one “faint” LED • 3 with two “faint” LEDs • 11 with one LED “far from the designed position” • 1 with two LEDs “far from the designed position” Up to now ~12 LEDs have been replaced (0.6 %) Max deviation from the designed position is 104 μm Precise work during the assembly!

  17. Backup slides

  18. Measurement program For each fork the coordinate systems for the cameras and the table are matched. A spot is found if the centroid distance from the predetermined sensor point is < 0.03 pixel Centroid calculation: The image (384x288 pixels which is equals to the physical resolution of the video-sensor) digitized into 8 bits. Any pixel below the threshold (presently 5) is set to zero. The range range of interest is found around the spot: The pixel with max brightness is found This pixel is considered to be part of the spot Walking around this pixel: the fact whether a pixel having nonzero content is a member of the spot depends on the number of its spot member neighbors.

  19. Analysis • Table coord -- tool coord • (with the matching of the two sides) • 2) Validity check of the measurements: • Average calculation -> • T-test (for N=5 the rejection above 2.57sigma) rejecting but keeping the measurement if • new average, etc. -> max-min of the valid measurements • 3) Transformation of valid average into the coordinate system of the fork

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