Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
54
Setting Up Feedback and Master Position Sensors
Conversion Table Processing Setup – MACRO Station Interface
If the quadrature encoder is connected to a remote MACRO Station, the conversion table processing
(usually 1/T extension) is done in the MACRO Station, and the resulting enhanced position information is
passed back to the Turbo PMAC, where it is processed by the Turbo PMAC’s encoder conversion table as
unshifted parallel data (usually method digit $2, mode switch bit = 1), because it already has fractional
count information, before use by the servo. For details of setting up the encoder conversion table to
process quadrature encoders, consult the MACRO Station manuals, the section Setting up the Encoder
Conversion Table in the Turbo PMAC User Manual, and the specification for variables I8000 – I8191 in
the Software Reference Manual.
(usually 1/T extension) is done in the MACRO Station, and the resulting enhanced position information is
passed back to the Turbo PMAC, where it is processed by the Turbo PMAC’s encoder conversion table as
unshifted parallel data (usually method digit $2, mode switch bit = 1), because it already has fractional
count information, before use by the servo. For details of setting up the encoder conversion table to
process quadrature encoders, consult the MACRO Station manuals, the section Setting up the Encoder
Conversion Table in the Turbo PMAC User Manual, and the specification for variables I8000 – I8191 in
the Software Reference Manual.
Scaling the Feedback Units
The decoding scheme you select in the Servo IC or MACRO IC determines what a count is. For example,
if selecting times-4 decode, a count is defined as ¼ of an encoder line. If the encoder has 2000 lines per
revolution, a count is defined as 1/8000 of a revolution. All subsequent position, velocity, and
acceleration units are based on this definition of a count.
if selecting times-4 decode, a count is defined as ¼ of an encoder line. If the encoder has 2000 lines per
revolution, a count is defined as 1/8000 of a revolution. All subsequent position, velocity, and
acceleration units are based on this definition of a count.
Setting Up Digital Hall Sensors
Three-phase digital hall-effect position sensors (or their equivalent) are popular for commutation
feedback. They can also be used with Turbo PMAC as low-resolution position/velocity sensors. As
commutation position sensors, typically they are just used by Turbo PMAC for approximate power-up
phase position; typically, ongoing phase position is derived from the same high-resolution encoder that is
used for servo feedback. (Many controllers and amplifiers use these hall sensors as their only
commutation position feedback, starting and ongoing, but that is a lower-performance technique.
feedback. They can also be used with Turbo PMAC as low-resolution position/velocity sensors. As
commutation position sensors, typically they are just used by Turbo PMAC for approximate power-up
phase position; typically, ongoing phase position is derived from the same high-resolution encoder that is
used for servo feedback. (Many controllers and amplifiers use these hall sensors as their only
commutation position feedback, starting and ongoing, but that is a lower-performance technique.
Many optical encoders have hall tracks. These commutation tracks provide signal outputs equivalent to
those of magnetic hall commutation sensors, but use optical means to create the signals.
those of magnetic hall commutation sensors, but use optical means to create the signals.
Note:
These digital hall-effect position sensors should not be confused with analog hall-
effect current sensors used in many amplifiers to provide current feedback data for
the current loop.
effect current sensors used in many amplifiers to provide current feedback data for
the current loop.
Signal Format
Digital hall sensors provide three digital signals that are a function of the position of the motor, each
nominally with 50% duty cycle, and nominally one-third cycle apart. (This format is often called 120
nominally with 50% duty cycle, and nominally one-third cycle apart. (This format is often called 120
o
spacing. Turbo PMAC has no automatic hardware or software features to work with 60
o
spacing.) This
format provides six distinct states per cycle of the signal. Typically, one cycle of the signal set
corresponds to one electrical cycle, or pole pair, of the motor. These sensors, then, can provide absolute
(if low resolution) information about where the motor is in its commutation cycle, and eliminate the need
to do a power-on phasing search operation.
corresponds to one electrical cycle, or pole pair, of the motor. These sensors, then, can provide absolute
(if low resolution) information about where the motor is in its commutation cycle, and eliminate the need
to do a power-on phasing search operation.