What is the accuracy on the UNITS / REP_DIST?
Q:
What is the
accuracy on the UNITS / REP_DIST?
UNITS = 2^23*3/360 ' Counts/deg
REP_DIST = 180 ' deg
REP_OPTION = 0
' [-REP_DIST..REP_DIST]
As UNITS is
approx. 69905.0667 then what will happen when I have run the system for several
hours?
Will I
loose accuracy over time?
=============================================================================================================
A:
The motion operates
in counts and all the values are stored as Integers. (64 bit on the
MC4/5/6 ranges)
UNITS is used to
present engineering values to the user and to the programs. Therefore when you set
REP_DIST = 180, the value that is stored is INT(180 * UNITS). When the axis
parameters or program reads back REP_DIST it shows the internal repdist /
UNITS.
UNITS is a
float. So your UNITS is 2^23 * 3/360 = 69,905.0666667. The
recurring decimal is a sign that you may get errors over a long time, but let’s
check the REP_DIST;…
REP_DIST = 180 is
stored as 180 * 69,905.0666667 = 12582912. That is an exact
integer. However there is always a chance that the FP maths could have a
small error that could make it 12582911.999999 and the integer would be
12582911
The safest way is
to set the REP_DIST with UNITS 1 using the exact counts.
UNITS = 1
REP_DIST = 12582912
REP_OPTION = 0
UNITS = 2^23*3/360
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