Rockwell Automation 1398-PDM-xxx IQ Master Version 3.2.4 for IA-2000 and IQ-5000 Positioning Drive Modules, IQ-55 - Manual (Page 286)

264 Language Reference • Reference
Publication 1398-PM601A-EN-P — October 2000
WORDS
SCALE Distance Scale System
Purpose This instruction defines the scale of the position feedback encoder, in steps per user
unit. The scale is defined to produce the desired user units (e.g., inches, centimeters,
revolutions) for all measured movements of the motor during the program. For this
reason the SCALE instruction should be executed before the execution of any motion
instruction. The required scale is calculated as follows: the number of encoder lines
multiplied by 4 multiplied by the mechanical ratio of the drive train.
Syntax SCALE = value
variable = SCALE
value The number of encoder counts per user unit of measure. Value
can be a constant, a nonvolatile variable Gn, a volatile variable
Vn, or a system variable. Value must be a whole number. Frac-
tional scales are not permitted.
variable The variable may be a nonvolatile variable Gn, a volatile vari-
able Vn, or a system variable.
Do not change scale unless home has been
defined. The scale statement should not be
used while an ULTRA Plus or IQ is executing
motion as unexpected motion may result. (The
motor may jump if there is a difference between
the new and old value.
Remarks Example: Assume that inches are the desired user unit. The motor has a 2000 line
encoder and therefore generates 8000 counts per revolution. The drive train consist of
a lead screw which makes 5 revolutions per inch of travel. The scale should be set to:
Changes made to this variable by a program are only in effect while the program is
running. When the program ends it will return to the value stored in the Personality
Module. If no change is made to this variable by the program, the value in the Person-
ality Module is used. The value in the Personality Module is set in the Parameter
menu, System dialog box.
See Also SCALE2, CF, “Conversions” on page 131
Example ;assume the condition of the above example
SCALE = 40000 ;set scale to 40000 count / inch
ATTENTION
!
Scale
counts
motor rev.
motor rev.
inch
Scale
40,000 counts
inch
= Ч
=
8000 5