Service manual

LUMISCAN ACR-2000 READER SERVICE MANUAL - SECTION 5.0 SERVICE ADJUSTMENTS
5-4
5.3 Scan Linearity Adjustment
NOTE
This Adjustment Must be done in a Darkened Room
NOTE
Adjustment of the Scan Linearity is rarely necessary. For various reasons, the Linearity Test can
sometimes provide a false indication of failure. Test results which are slight out of tolerance are probably
genuine. Test results which are far out of tolerance are likely false. The most common reason for false
Test results is too much ambient light leaking into the unit. Be sure to verify that the Scan Linearity is
failing before making any adjustments
This adjustment will assure that the reading of a single line of data occurs within the most linear region of a
given Galvo motor sweep, and that the edges of the film do not fall outside of the scan range.
The test pattern used in this adjustment has 14 evenly spaced bars of equal width. R45 Damping and
R47 Servo Gain on the Galvo PCA are used to adjust the rate of beam movement across the 14 bars
so that the number of pixel samples on each bar is the same. If the beam moves too slowly across a bar
the number of pixel samples will be too high. This error is quantified by the LNADJDT program as
CAL+. Conversely, too few pixel samples result in CAL- error. R58 Galvo Offset is used to position
the beam so that the 14 bars are centered in the beam span . R59 Galvo Span is used to adjust the
beam span so that the sum of the 14 bar widths is a specified value called Sum of Deltas, which is the
sum of the pixel samples of the 14 bars. The field specification for these parameters is as follows.
Nominal Parameters
Cal + error: less than 2%
Cal - error: less than 2%
Sum of Deltas: 3902 + 1
Distance to first edge: 86 + 1
Preferred Parameters
Cal + error: less than 3%
Cal - error: less than 3%
Sum of Deltas: 3902 + 8
Distance to first edge: 86 + 3
Allowable Parameters
Cal + error: less than 5%
Cal - error: less than 5%
Sum of Deltas: 3902 + 20
Distance to first edge: 86 + 7
5.3.1 The room lights should be dim and the unit covered to minimize stray light.