Cognex In-Sight 1721, User Manual

Page: 39 / 156

In-Sight
®
1700 Series Wafer Reader Section 3: Configuring a Wafer ID Application
29
NOTE Using one of the predefined entries (*, A, N, H, D, C, S, X, dot, dash, space) in the Field Definition
will remap the list of valid characters to the new definition. Therefore, it is strongly recommended
that you do not use a predefined field definition.
Example : If the Field Definition is &=123;$=3456;%=789, and the Field String is
&$%*******CS, then the only characters that will be valid in the first position will be 1, 2, or
3. The only valid characters in the second position will be 3, 4, 5, or 6. And in the third
position, only 7, 8, or 9 will be valid.
3.5.7 Accept
The Accept value specifies the minimum response threshold for the raw reading score
(40 to 100; default = 50). The meaning of the Accept value and its role in determining the
pass/fail status of a read depends on the type of wafer mark.
In all cases, before a read can be considered successful, the raw score must exceed the
Accept threshold. Only then will the bonus points for passing the checksum be added to
the raw score, and the pass/fail status of the read determined.
Characters . The response score for a character string is derived from the average of
the individual scores for all characters in the string. Refer to Section 3.5.5 for a
detailed explanation of how the raw score combines with a checksum to determine
the total score and pass/fail status of the read.
NOTE It is possible for the raw score to exceed the Accept value even when individual character
scores fall below the specified threshold, as long as each individual character scores above
the Character Threshold. This allows character strings where all but one or two characters
score above the threshold to be read successfully.
2D symbol. The response score for a 2D symbol is the score for locating the mark in
the image. If the 2D mark cannot be located, the score will be 0 and the read fails. If
the 2D mark is located and the mark is decoded, 300 bonus points are added to the
raw score (passed scoring range: 340 – 400).
NOTE Accept is ignored when ‘2D Sym, T7 Data Matrix’ is the selected Mark type.
Barcode. The response score for a barcode is the percentage of “scan lines” within
the Region that correctly detect the length of the string encoded in the barcode. If at
least three scan lines decode the same string that passes the checksum, 300 bonus
points are added to the raw score (passed scoring range: 310 – 400).
NOTE Accept is ignored when a barcode is the selected Mark type.
3.5.8 Character Threshold
When ‘Chars, SEMI’, ‘Chars, IBM’ or ‘Chars, Triple’ is the selected Mark, the Character
Threshold value specifies the minimum response threshold for each individual character
score (25 to 100; default = 25). Each individual character score must be greater than the
Character Threshold or the read will fail.