Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
62
Setting Up Feedback and Master Position Sensors
Motor offset variable Ixx26 contains the difference between the absolute resolver position and the
resulting motor position (if any).
resulting motor position (if any).
Scaling the Feedback Units
The Acc-8D Option 7 R/D converter is a 12-bit converter. It reports 4096 separate states per electrical
cycle of the resolver (per mechanical revolution for a typical 2-pole resolver, per half revolution for a 4-
pole resolver). It reports this as a 12-bit binary number if queried for absolute position over the
multiplexer port. For ongoing position, it generates 1024 digital quadrature cycles per electrical cycle,
which creates 4096 counts per cycle after times-4 decode.
cycle of the resolver (per mechanical revolution for a typical 2-pole resolver, per half revolution for a 4-
pole resolver). It reports this as a 12-bit binary number if queried for absolute position over the
multiplexer port. For ongoing position, it generates 1024 digital quadrature cycles per electrical cycle,
which creates 4096 counts per cycle after times-4 decode.
Setting Up MLDTs
A Turbo PMAC with PMAC2-style ICs can provide direct interface to magnetostrictive linear
displacement transducers (MLDTs), such as MTS’s Temposonics brand. MLDTs can provide absolute
position information in rugged environments; they are particularly well suited to hydraulic applications.
In this interface Turbo PMAC provides a periodic excitation pulse output to the MLDT, receives the echo
pulse that returns at the speed of sound in the transducer, and very accurately measures the time between
these pulses, which is directly proportional to the distance of the moving member from the stationary base
of the transducer. The timer therefore contains a position measurement.
displacement transducers (MLDTs), such as MTS’s Temposonics brand. MLDTs can provide absolute
position information in rugged environments; they are particularly well suited to hydraulic applications.
In this interface Turbo PMAC provides a periodic excitation pulse output to the MLDT, receives the echo
pulse that returns at the speed of sound in the transducer, and very accurately measures the time between
these pulses, which is directly proportional to the distance of the moving member from the stationary base
of the transducer. The timer therefore contains a position measurement.
MLDT Interface Type
MLDTs are available with several different interface formats; for this interface, a format with external
excitation is required, because Turbo PMAC provides the excitation pulse. Usually, this format has an
RS-422 interface, because the excitation and echo pulses are at RS-422 levels. The Turbo PMAC MLDT
interface inputs and outputs are at RS-422 levels.
excitation is required, because Turbo PMAC provides the excitation pulse. Usually, this format has an
RS-422 interface, because the excitation and echo pulses are at RS-422 levels. The Turbo PMAC MLDT
interface inputs and outputs are at RS-422 levels.
Some MLDTs come with internal excitation and computation of position, providing a position value in a
format such as Synchronous Serial Interface (SSI) or an analog voltage. In these cases, setting up the
Turbo PMAC interface is dependent only on the data format, not on the underlying principle of the
sensor. Refer to the appropriate feedback-format section for details.
format such as Synchronous Serial Interface (SSI) or an analog voltage. In these cases, setting up the
Turbo PMAC interface is dependent only on the data format, not on the underlying principle of the
sensor. Refer to the appropriate feedback-format section for details.
Signal Formats
There are two common signal formats of the external excitation type; MTS calls them RPM and DPM. In
the RPM format there are two short pulses returned from the MLDT: an immediate start pulse, and a
delayed stop pulse.
the RPM format there are two short pulses returned from the MLDT: an immediate start pulse, and a
delayed stop pulse.
RPM Signal Format
Pulse Out
Return
Start
Stop
Since Turbo PMAC uses the first rising signal edge returned after the falling edge of the output pulse to
latch the timer, the key setup issue in this format is to make sure that the output pulse width is large
enough so that the falling edge of the output pulse occurs after the rising edge of the return line’s start
pulse (see PFM Pulse Width below).
latch the timer, the key setup issue in this format is to make sure that the output pulse width is large
enough so that the falling edge of the output pulse occurs after the rising edge of the return line’s start
pulse (see PFM Pulse Width below).
In the DPM format, there is only one long pulse returned from the MLDT.
DPM Signal Format
Pulse Out
Return
Start
Stop