Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 60)

Chapter 4
Configuring Your Decoder
4–33
Note: The timers (No-Read & Inter-Scan) have an accuracy of
±
5
milliseconds.
To assist you in setting the inter-scan timer, we have provided the following
guidelines. These guidelines will only allow you to approximate the setting
of the timer. Since many factors, including label quality, determine when the
first read occurs, you may have to try several different timer settings before
finding a setting for your application.
Refer to Figure 4.5. The inter-scan timer setting can be approximated using
the following equation:
d (inches) X 1000 (msec/sec)
Line Speed (inches/sec )
Approximate Inter-Scan Timer
Value (msec)
=
Figure 4.5
Setting Inter-Scan Timer
x
Direction of Travel
Scan
Line
d
D
Field# 1
Field# 2
In Figure 4.5, the decoder will decode Field #1, start the inter-scan timer,
stop decoding, and wait for the timer to time out. The decoder will then
resume decoding. When the timer times out, Field #1 will be x distance
behind the scan line. The distance x is measured from the trailing edge of
Field #1 and will be a value between zero and d depending upon where the
scan line was in Field #1 when the valid read occurred.