Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive - Air-Cooled (A Frame) - Manual (Page 336)

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Component Definition and Maintenance
7000A-RM001A-EN-P – January 2011 7000 “A” Frame
Binary Code Gray Code
255 011111111 010000000
256 100000000 110000000
All nine bits changed in the Binary Code while only the MSB of the
Gray code changed. In the Universal Encoder Interface there are
delays created by the frequency filter components and input
hysteresis. Differences in these delays could cause errors due to
reading a bit as ON when it is actually transitioning to OFF or vice
versa. In the case of Gray code since only one bit ever changes the
ambiguity error is never more than one count. For this reason and to
reduce inrush currents, Rockwell Automation recommends using
Gray code Positional Encoders.
2.
Data Polarity: Absolute encoders typically have a High True output.
If the encoder model does not have a High/True (or Non
Inverted/Inverted) option you should assume it to be High True. In the
case of a 10bit High True encoder the zero position is represented by
0000000000. Whereas a Low/True encoder the zero position is
1111111111. On the Universal Encoder Interface the position data is
inverted in hardware. That is a ‘1’ will turn on an Optocoupler
producing a ‘0’. Therefore a High True encoder would produce
1111111111 for the zero position. With the POL_QRDNT jumper you
can control the polarity of the input. With the jumper installed
(factory default) it is setup to accept High True encoders and an extra
inversion is done in the Universal Encoder Interface. If you are using
a Low True encoder then this jumper needs to be removed so that the
zero position is inverted by the optocouplers alone.
The other role of the POL_QRDNT jumper is to correct the data in
the event the encoder was mounted so that a CCW rotation produced
decrementing counts. If this is the case the POL_QRDNT jumper
should be configured to the opposite of what it should normally be for
the data polarity. For example if the Universal Encoder Interface is
configured to operate with High True encoders (POL_QRDNT
installed), remove it to correct for encoder mounting.