User's Manual

PMAC2 User Manual
78 Setting Up PMAC2 for MLDT Feedback
Scaling the Feedback Units
Motor Units
For a motor set up with MLDT feedback, a count is one increment (LSB) of the timer. The physical
length of this increment, which is the resolution of the measurement, is dependent on the speed of the
return pulse in the MLDT, and the frequency of the timer in the PMAC2. The speed of the return pulse
varies from device to device, but is always approximately the inverse of 0.35 µsec/mm, or 9.0 µsec/inch.
The frequency of the timer is 117.96 MHz. The resolution can be calculated as:






≅≅






≅≅














=






inch
increments
1060
increment
inches
00094.0
sec
inches
0.9
1
*
increment
sec
96.117
1
mm
increments
3.41
increment
mm
024.0
sec
mm
35.0
1
*
increment
sec
96.117
1
sec
length
dReturnSpee*
increment
sec
TimerFreq
1
increment
length
Resolution
µ
µ
µ
µ
µ
µ
Axis User Units
Typically, the axis assigned to the motor using the MLDT for feedback will be given engineering units of
millimeters or inches. The scaling is done in the axis definition statement. With the above example, an
axis definition statement to create axis user units of millimeters would be:
#1->41.3X
An axis definition statement to create axis user units of inches would be:
#1->1061X