- General Electric Computer Accessories User Manual

GEH-6385 Reference and Troubleshooting, 2300 V Drives Chapter 3 Paramters/Functions •
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• 3-13
Position Feedback
The Position Feedback function provides a set of position feedback signals in 22-bit
floating point format.
Function inputs
The following tachometer signals are inputs to the Position Feedback function.
• Tachometer position: This signal is a 16-bit integer with units of A-quad-B
counts.
• Marker count: This signal is a 16-bit integer that increments every time a marker
pulse is detected.
• Marked tachometer position: This signal is a 16-bit integer with units of A-quad-
B counts. It equals the tachometer position at the instant the marker pulse is
detected.
The following table specifies the input parameters of the Position Feedback function.
Parameter Description
Pos sample cmd sel
Selects the signal that specifies the sampling of
tachometer position.
Function outputs
The following table specifies the output variables of the Position Feedback function.
Variable Description
Position counter
Tachometer position extended to 22 bits and
converted to floating point format.
Pos cntr mark
Marked tachometer position extended to 22 bits and
converted to floating point format.
Pos down edge smp
Sampled version of Position counter, sampled on the
falling edge of the sample signal.
Pos up edge sample Sampled version of Position counter, sampled on the
rising edge of the sample signal.
Function description
The output signals Position counter and Pos cntr mark are the tachometer position
and the marked tachometer position extended from 16 to 22 bits. Position counter
and Pos cntr mark roll over to zero (0) at the maximum value that can be represented
in 22 bits (4,194,303). The transition happens in both the forward and backward
directions.
Position counter is sampled when the signal selected by Pos sample cmd sel
transitions between True and False. Pos up edge sample equals Position counter
when the signal selected by Pos sample cmd sel changes from False to True. Pos
down edge smp equals Position counter when the signal selected by Pos sample cmd
sel changes from True to False.
The Task Interval Strobe shown on the Position Feedback diagram represents
sampling of hardware that takes place at the Task 1 rate, the fastest execution rate
available to the control. The Task 1 rate is faster than the fastest rate at which
Position counter can be sampled.
Related diagrams
• Position Feedback Instrument (PosFbk)