Delta MMC120 User Manual
Page 30
Motion Control Parameters
MMC120 Linear Motion Control Module
30
Delta Computer Systems, Inc. 360/254-8688
SCALE (Default: 30300) Range: -32767 to 32767, excluding 0
See the Startup section (page 20) for additional information.
TIP: Use DCS120 commands P0 and P1 to help calculate SCALE and OFFSET.
The SCALE parameter is used to calculate the ACTUAL POSITION in Position Units from the
TRANSDUCER COUNTS. Position Units can be 0.001", 0.1 mm, etc. The primary use for the SCALE
parameter is to compensate for variations in magnetostrictive transducers. It can also be used to convert to
non-standard units for special applications.
SCALE is defined as 32768 times the number of Position Units per TRANSDUCER COUNT:
(P0 - P1)
SCALE =
x 32768
(C0 - C1)
Where P0 and P1 are two positions and C0 and C1 are the corresponding transducer counts.
Magnetostrictive displacement transducers have a calibration number (nominally 9.012 microseconds per
inch) and the MMC120 has a 60 MHz oscillator with both edges counted, for an effective counter speed of 120
MHz. To determine the SCALE for a magnetostrictive transducer use the following formula:
Position Units per Inch x 32768
SCALE =
x Sign
Cal. Number (
µ
s/in) x 120 (MHz)
Where
Sign
equals +1 when an extend move yield increasing ACTUAL POSITION counts, and it equals -1
when an extend move yields decreasing ACTUAL POSITION counts. Negative SCALE values indicate the
axis moves in reverse. That is, the ACTUAL POSITION decrease as the TRANSDUCER COUNTS increase.
The calibration number must be specified in the same units as the Position Units (inches, mm, etc.). Position
Units are generally 0.001 inches or 0.1 mm. Usually there are 1000 Position Units per inch when the
calibration number is in microseconds per inch.
The ACTUAL POSITION is determined as follows:
TRANSDUCER COUNTS x SCALE
ACTUAL POSITION =
+ OFFSET
32768
NOTE: When the SCALE parameter is changed, the EXTEND LIMIT, RETRACT LIMIT, and OFFSET must also
be changed.
SCALE Calculation Examples
Example 1
For a system using a magnetostrictive transducer with a calibration number of 9.0110
µ
s per inch and
a position unit of 0.001 inch, the SCALE will be:
1000(Position Units Per Inch) X 32768
SCALE =
= 30304