Accessory 24E2S
MLDT Feedback for UMAC-Turbo & UMAC-MACRO
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MLDT FEEDBACK FOR UMAC-TURBO & UMAC-MACRO
The Acc-24E2S can provide direct interface to magnetostrictive linear displacement transducers
(MLDTs) through its encoder connectors. This interface is for MLDTs with an external excitation format
(often called RS-422 format because of the signal levels). The Acc-24E2S provides the excitation pulse,
and receives the echo pulse, both with RS-422 signal formats.
This section provides basic information for using MLDTs with the Acc-24E2S. More information can be
found in the User Manuals for the Turbo PMAC or the MACRO Station.
MLDT Hardware Setup of the Acc-24E2S
The Acc-24E2S must be set up to output the differential pulse on what is normally the T and W input
flags on the encoder connector. This is done by setting the jumper setting to 1-2 on E-points E1 for
channel 1, E2 for channel 2, E3 for channel 3, and E4 for channel 4. These jumpers are set to 1-2
configuration by default.
The PULSE+ (high during the pulse) and PULSE- (low during the pulse) outputs from the encoder
connector are connected to the differential pulse inputs on the MLDT. The echo pulse differential outputs
from the MLDT are connected to the CHA+ and CHA- input pins on the same encoder connector.
If the MLDT uses RPM format, in which there is a brief start echo pulse, and a brief stop echo pulse, the
“+” output from the MLDT should be connected to the CHA+ input on the Acc-24E2S, and the “-” output
should be connected to the CHA- input.
If the MLDT uses DPM format, in which there is a single long echo pulse, with the delay to the trailing
edge measuring the position, the “+” output from the MLDT should be connected to the CHA- input on
the Acc-24E2S, and the “-” output should be connected to the CHA+ input.
MLDT Software Setup of the UMAC Turbo
When the Acc-24E2S is used for MLDT feedback in a UMAC Turbo system, a few I-variables must be
set up properly.
Hardware Setup I-Variables for Servo IC m
I7m03 (PFM Clock Frequency):
In almost all cases, the clock frequency driving the pulse-generation
circuitry for all channels on Servo IC m can be left at its default value of 9.83 MHz (0.102
sec). I7m03
also controls other clock signal, has a default value of 2258 and rarely needs to be changed.
I7m04 (PFM Pulse Width):
The pulse width, set by I7m04 in units of PFM clock cycles must be set
long enough for the MLDT to see, and long enough to contain the rising edge of the RPM start echo
pulse, or the rising edge of the single DPM echo pulse. For example, if this edge can come up to 2
sec
after the start of the excitation pulse, and the PMAC clock cycle is at its default of about 0.1
sec, then
I7m04 must be set at least to 20.
I7mn6 (Output Format Select):
For Servo IC m Channel n to be used for MLDT feedback, I7mn6 must
be set to 1 or 3 for the C sub-channel to be used for PFM-format output. On an Acc-24E2A, I7mn6 must
then be set to 3 for the A and B sub-channels to be used for DAC-format output.
I7mn0 (MLDT Feedback Select):
For Servo IC m Channel n to be used for MLDT feedback, I7mn0
must be set to 12. In this mode, the pulse timer is cleared on the output pulse, and latched on the echo
pulse, counting in between at 117.96 MHz.
Conversion Table Processing I-Variables
The pulse timer for Servo IC m Channel n holds a number proportional to the time and therefore the
position. This must be processed in the conversion table before it can be used by the servo loop. It is best
to use the filtered parallel data conversion, a 3-line entry in the table (three consecutive I-variables).
