Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive - Air-Cooled (A Frame) - Manual (Page 335)

Component Definition and Maintenance 5-93
7000 “A” Frame 7000A-RM001A-EN-P – January 2011
A T T E N T I O N A T T E N T I O N When the drive switches over to the
redundant encoder, it cannot switch back
without recycling control power.
Positional Encoder Operations
Besides quadrature encoders, the Universal Encoder Interface will also
accept positional (absolute) encoders. Parallel positional data is converted
to a serial stream and transmitted to the DPM when requested by the drive.
The board will also generate “pseudo” quadrature differential signals,
including a zero position mark, derived from the binary data to the DPM.
There are three different positional encoder configurations available. For
all of these configurations remove the ENC_TYPE jumper. The other
jumpers configure the board for the type of positional data (Gray Code or
Natural Binary) set by CD_DQUAD and High or Low True data set by
POL_QRDNT.
1.
Gray code, Low True. In this configuration the board will invert the
incoming gray code data and then convert it to binary for transmission
to the DPM.
2.
Natural Binary, Low True. No conversion is done on the incoming
data but it is inverted.
3.
Gray code, High True. In this configuration, the incoming gray code
data is simply converted to binary. No inversion is done on the input
data.
4.
Natural Binary, High True. The positional data is simply converted
to the serial stream. No inversion or conversion is done on the data.
Consult factory for availability of Positional Encoders.
Positional Encoder Guidelines
When selecting a positional encoder there are certain guidelines that
should be followed for optimal performance.
1.
Code Selection: Absolute encoders can be purchased with either
Gray code or Binary output format. Gray code is a form of binary
code where only a single bit changes at a time for each sequential
number or position. The fact that only a single bit changes at a time
make it easier for the Universal Encoder Interface to read valid
positional data and not ambiguous data. If we compare the Natural
Binary code to Gray code for the transition from 255 to 2556, here is
what we get: