Rockwell Automation 1771-QB Linear Pos. - Manual (Page 75)

Interpreting ModuleĆtoĆPLC Data
(READS)
Chapter 6
6Ć14
Measured Velocity (words 20 and 21)
Measured velocity is the instantaneous speed of the axis measured at the
transducer. This velocity is calculated using a moving average over the previous
20, 50 or 100 milliseconds (depending on the velocity commanded for the
move). For slow moves, a 100 millisecond averaging interval is used to improve
resolution. For fast moves, a 50 or 20 millisecond averaging interval is used to
improve responsiveness.
Measured velocity is always positive, regardless of the direction of travel.
Table 6.B
Averaging Interval for Various Commanded Velocities
Commanded Velocity Averaging Interval
ips mmps
0.00 Ć 10.00 0 Ć 254.0 100 ms
10.01 Ć 20.00 254.1 Ć 508.0 50 ms
> 20.00 > 508.0 20 ms
Figure 6.9
Measured Velocity Format
50005
Measured velocity.
BCD 99.99 ips or 999.9 mmps max
Binary 327.67 ips or 3276.7 mmps max
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
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Desired Velocity (words 22 and 23)
The module calculates the desired velocity once every two milliseconds based
on the acceleration, deceleration and velocity specified for the move. The
desired velocity is a theoretical number representing the speed that the module
wishes to achieve, and not necessarily the actual velocity of the axis. The
desired velocity is always positive, regardless of the direction of travel.