VMC 186/40 Motion Control Module Control Parameters
17
The value used for the
Scale
parameter is affected by the number or recirculations selected (hardware jumper).
Recirculation selection is based on the transducer length and desired position resolution. When using four
recirculations, the most common position resolution is 0.0005". With two recirculations, the position resolution
is usually 0.001" and with one recirculation it is 0.002" or 0.05 mm. For more information on recirculation see
page 33.
Linear transducers have a calibration number (typically 9.1
µ
s per inch) and the VMC 186/40 has a 55.5 MHz
oscillator for transducer position measurement counters. To determine the
Scale
for a magnetostrictive
transducer use the following formula:
32768
Scale
=
Position Unit * Cal Number * 55.5 * Number of Recirculations
The calibration number must be specified in the same base units as the position units (inches, mm, etc.). If the
calibration number is expressed in inches then position units would be expressed in inches (i.e. 9.1392
microseconds per inch for a calibration number and .001 inch resolution is desired)
The
Scale
parameter can also be adjusted or fine tuned by using position readings from the VMC 186/40 and
actual physical measurements in the following formula:
Position Reading 1 - Position Reading 2
Scale
= Old Scale *
Measured Position 1 - Measured Position 2
Where Old Scale is the default
Scale
or a previously calculated
Scale,
and measured position is in position units
(thousandth of an inch, etc.) from a physical measurement of the system. Position readings are taken using the
Actual Position
parameter.
Note: If a negative value is obtained for
Scale
, the absolute value must be used and the
Direction
parameter
changed from 0 to -1 or vice versa. Also, when the
Scale
parameter is changed, the
Extend Limit, Retract Limit
and
Offset
must also be changed.
