Failures over useful life are random but have an average rate: Poisson Process - PowerPoint PPT Presentation

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Result #3:. # Failures/yr = #Units * S l i = 7.20. Reliability Analysis of a Low Voltage Power Supply Design for the Front-End Electronics of the ATLAS Tile Calorimeter. Gary Drake, Member IEEE , James Proudfoot Argonne National Laboratory, Lemont, IL USA.

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Failures over useful life are random but have an average rate: Poisson Process

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Failures over useful life are random but have an average rate poisson process

Result #3:

# Failures/yr = #Units * Sli = 7.20

Reliability Analysis of a Low Voltage Power Supply Design

for the Front-End Electronics of the ATLAS Tile Calorimeter

Gary Drake, Member IEEE,

James Proudfoot

Argonne National Laboratory, Lemont, IL USA

Abhirami Senthilkumaran, Bruce Mellado,

Anusha Gopalakrishnan, Sanish Mahadik

University of Wisconsin-Madison, Madison, WI USA

On Behalf of the ATLAS Tile Calorimeter System

The TileCAL Low Voltage System

LVPS Brick

  • Power for TileCAL Front-End Electronics

  • Novel Switching DC-DC Power Supply

    • Custom, Compact, High-Efficiency, 250 Watt

    • 8 Different Voltages  Customized Bricks

    • Water Cooled; System Interface & Monitoring

    • Environment: Magnetic Field, Radiation Tolerant

  • 256 boxes on detector, 2048 bricks, + spares

  • Reliability is Important  Infrequent Access

LVPS Box

8 bricks per Box

LVPS

Access

on

Detector

Detector Section

End of Long Barrel

Drawer Electronics

We have performed a reliability analysis on the new upgraded supplies  2048 Bricks in the detector system

Reliability Analysis Methodology

  • Mean Time Between Failures MTBF

    • Expected time between failures

    • MTBF = 1 / l

    • This is not “useful lifetime”

  • Probability of Failure-Free Operation

    • Probability of no failures at time t

    • R(t) = e-lt

    • Must calculate l for the entire unit

  • Failures over useful life are random but have an

    average rate: Poisson Process

  • Probability of k failures between time t and t+t:

     Poisson Distribution

  • Failures in Electronics

    • Failures generally

      described by the

      Bathtub Curve

    • Interested in region of

      Constant Failure Rate

  • l = Average number of units failing per unit time

  • Measured in Failures In Time FITS (# / 109 hrs)

Calculations

  • Comparison with Previous Design

    • Rated voltage of capacitor is 20V

    • Calculated failure rate: 12.4 bricks/year

    • Observed failure rate: 5.2 bricks/year

      • From 3 years of operation

  • Series-Parallel Model and

    • Voltage De-rating for Capacitor

    • Tantalum capacitors most critical

    • Rated for 35V, used at <= 15V

    • Higher voltage rating reduces failure

  • When a capacitor fails

    • Probability of short = 0.75; Probability of open = 0.25

    • Also include 4 caps in parallel + diodes + LC filter

  • Series Reliability Model

    • Any single failure can cause brick to fail

    • Use only critical parts in model

  • Assume

    • Part failures are independent & random

    • Start with single tantalum cap

  • Parts Count Method

    • Use FITS values for each part

  • Statistical Analysis

    • Poisson distribution; Neyman procedure

  • Use observations as a correction

# Failures/yr = # Units * S [li * wi] X x

# Failures/yr = #Units * S [li * wi] = 5.03

Result #1:

Result #2:

  • Expect 2.11 failures per year in the system

  • Still Dominated by Tantalum Reliability

  • Dominated by Tantalum Reliability


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