Delta MMC120 - Manual (Page 110)

110
SCALE
Default: 30300
Range: -32767 to 32767, excluding 0
TIP: From the Tools menu, select Scale/Offset Calibration to help calculate
SCALE and OFFSET .
The SCALE parameter is used in calculating the ACTUAL POSITION in Position Units
from the TRANSDUCER COUNTS , using the following formula (Position Units can be
0.001", 0.1 mm, etc.):
ACTUAL POSITION = TRANSDUCER COUNTS x SCALE +
OFFSET
32768 x Prescale Divisor
In linear position applications, SCALE accounts for the following:
1.Transducer Compensation: The SCALE parameter compensates for differences in
magnetostrictive transducers. Each transducer will indicate a different physical
distance for a given interrogation cycle. Usually, only a small change from the
default value is necessary to compensate the transducer.
2. Distance Translation: A second and more useful feature of SCALE is its ability to
translate a fixed physical distance to usable position units (position units from
thousandths to hundredths or vice versa). The translation is done using a combination
of SCALE and recirculation selection.
SCALE is defined as 32768 times the number of Position Units per TRANSDUCER
COUNT times the Prescale Divisor, as shown in the following equation (P0 and P1 are
two positions, C0 and C1 are the corresponding TRANSDUCER COUNTS , and the
Prescale Divisor is specified in the CONFIGURATION WORD ):
SCALE = (P0 – P1) x 32768 x Prescale Divisor
(C0 - C1)
The SCALE can be calculated on a magnetostrictive displacement transducer using its
calibration number (nominally 9.012 microseconds per inch) with the following formula:
SCALE = Position Units per Inch x 32768 x Prescale Divisor
x Sign
Cal. Number ( µ s/in) x 120MHz x # of
Recirculations
In the above formula, the 120MHz comes from the motion module’s internal counter, and
Sign equals +1 when an extend move yields increasing ACTUAL POSITION counts,
and -1 when an extend move yields decreasing ACTUAL POSITION counts.
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.