User`s manual

1-6 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual – January 2001 GFK-1742A
1
DSM314 Position Strobes
Each axis connector on the DSM314 faceplate has two Position Strobe inputs. A rising edge pulse
on a Strobe input causes the axis
Actual Position
to be captured. The position capture resolution
is +/- 2 counts with an additional 10 microseconds of variance for the strobe input filter delay.
The actual error seen is dependent upon servo acceleration and strobe input filtering/sampling.
Consult Appendix G for the exact formulas used to calculate strobe accuracy.
The strobe data is updated within one position loop update interval (0.5 - 2 ms) in the associated
Strobe Position
%AI data register. The
Strobe Position
data is also stored in a DSM Parameter
Register that can be used as an operand for Motion Program PMOVE and CMOVE commands
and in Local Logic. The
Strobe Position
data update to the PLC is dependent on the PLC sweep
time and may take longer than 2 ms.
In Digital mode, these strobes are 5V single-ended/differential inputs (IN1-IN2).
In Analog mode, these strobes are only 5V single-ended (IO5-IO6). In Analog mode only, these
strobe inputs are pulled high (as seen in the PLC %I Strobe status bits) if not physically connected
to a device.
DSM314 Scan Time Contribution
The table below lists how many milliseconds the DSM314 adds to PLC scan time. The amount of
scan time contribution is related to (1) the number of DSM314 axes configured, and (2) the type
of rack (main, expansion, or remote) the DSM314 is mounted in.
DSM314 Scan Time Contribution (in Milliseconds)
No. of Axes
Configured Main Rack Expansion Rack Remote Rack
1 1.6 2.6 6.9
2 2.2 3.8 9.9
3 2.8 4.3 13.0
4 3.3 5.2 15.9
Notes
1. Be aware that the DSM314’s internal Local Logic engine has a maximum
scan time of 2 ms that is independent of the PLC scan; therefore, time-
critical, motion-related I/O should be handled in the Local Logic program
rather than in the PLC ladder program. See the applicable chapters in this
manual for details on Local Logic programming.
2. For applications where the above additions to scan rates will affect machine
operation, you may need to use the “suspend I/O,” “DOIO,” and “SNAP”
features to transfer necessary data to and from the DSM314 selectively.
These features let you avoid transferring all of the %I, %Q, %AI, %AQ data
every scan if you do not require it that frequently, which would reduce the
scan time contribution amount.