Unused Error Correction

NI Vision 2015 Concepts Help

Edition Date: June 2015

Part Number: 372916T-01

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Unused error correction tests the extent to which regional or spot damage in the symbol has eroded the reading safety margin that the error correction provides.

The convolutional error encoding for Data Matrix codes ECC 000-ECC 140 can correct for the following maximum percentages of bit errors (Emax):
  • ECC 000: Emax = 0.0%
  • ECC 050: Emax = 2.8%
  • ECC 080: Emax = 5.5%
  • ECC 100: Emax = 12.6%
  • ECC 140: Emax = 25.0%

The actual percentage of bit errors (Eact) is the number of bits that were corrected divided by the total number of bits in the symbol data fields. The unused error correction for Data Matrix codes ECC 000-ECC 140 is expressed as

Unused Error Correction = 1.0 - (Eact / Emax)

For ECC 200 codes, the correction capacity of the Reed-Solomon decoding is expressed as

e + 2td - p

where e is the number of erasures
t is the number of errors
d is the number of error correction code words
p is the number of code words reserved for error detection

Values for d and p are defined by the specification for the given symbol. Values e and t are determined during a successful decode process. The amount of unused error correction is computed as

Unused Error Correction = 1.0 - (e + 2t) / (d - p)

In codes with more than one Reed-Solomon block, the unused error correction is calculated for each block independently, and the lowest value is used to calculate the unused error correction grade.

The following list shows how unused error correction is graded.
  • A (4.0) if unused error correction ≥ 0.62
  • B (3.0) if unused error correction ≥ 0.50
  • C (2.0) if unused error correction ≥ 0.37
  • D (1.0) if unused error correction ≥ 0.25
  • F (0.0) if unused error correction < 0.25

The following figure shows a Data Matrix code with an unused error correction value of 0.00, which returns a grade of F.


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