In-Sight
®
1700 Series Wafer Reader Section 3: Configuring a Wafer ID Application
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used as place-holders if the lot number is less than three digits. For example, if the
encoded lot number is “12”, the lot number would be reported as “012”. Reports settings
are ignored if ‘None’ is the selected Compression.
NOTE: For specific information on the customized decoding options, please contact your Cognex Sales
Engineer.
3.4.5 Checksum
The Checksum setting selects the method by which the read result from a character
string will be validated to ensure reliability, and establishes the scoring basis for
determining the pass/fail status of the read.
NOTE The Checksum setting is enabled and used only when ‘Chars, SEMI’, or ‘Chars, Triple’ is the
selected Mark. When any other Mark is selected, the Checksum setting is ignored.
In all cases, the raw read score of the character string must be higher than the specified
Accept threshold before the checksum will be evaluated (see Section 3.4.7). Then if the
character string passes its checksum, “bonus points” in increments of 100 and/or 200 are
added to the raw reading score and the read passes. The number of bonus points added
to the raw score depends on the Checksum selected.
When Virtual Checksum is selected by itself, the Accept threshold should be increased,
and the Field String & Field Definition should be made as specific as possible to limit the
list of possible characters at each position in the string. These steps will increase reading
reliability in the absence of a mathematical checksum.
SELECTION DESCRIPTION
Virtual
The Cognex Virtual checksum attempts to validate the read result using multiple reading methods.
If all methods read identical characters at each position in the string, the string passes the Virtual
checksum and 100 “points” are added to the raw response score.
This checksum should be used by itself only when the character string is known not to contain one
of the other checksums, and then a higher Accept threshold is strongly recommended.
Maximum score: 200 points
Minimum passed score: 100 plus Accept threshold
SEMI
Applies the SEMI-standard checksum and the Cognex Virtual checksum. If the read result passes
the SEMI checksum, 200 points are added to the raw score. If the read result also passes the
Virtual checksum and the results from both checksums agree, an additional 100 points are added
to the score.
The read must pass the SEMI checksum to be successful; if Virtual checksum passes but the
SEMI checksum fails, the entire read will fail.
Maximum score: 400 points
Minimum passed score: 200 plus Accept threshold
SEMI with Virtual
(default)
Applies the SEMI-standard checksum and the Cognex Virtual checksum. If the read result passes
the SEMI checksum, 200 points are added to the raw score. If the read result also passes the
Virtual checksum and the results from both checksums agree, an additional 100 points are added
to the score.
The read must pass both the SEMI and Virtual checksums to be successful; if either checksum
fails, the entire read will fail.
The SEMI with Virtual checksum selection is the most reliable method of validating a character
string containing a SEMI checksum.
Maximum score: 400 points
Minimum passed score: 300 plus Accept threshold
