8
8-16
FM 351 Positioning Function Module
EWA 4NEB 720 6001-02
8.6 Resolution
The resolution is not a direct item of machine data. It is however found by
the FM 351 from the two items of machine data:
Displacement per encoder revolution.
Pulses per encoder revolution.
With incremental encoders the quadruple evaluation is also taken into ac-
count.
The resolution is a measure for the accuracy of the positioning. It also deter-
mines the maximum possible travel range.
The travel range is limited by the number representation in the FM 351. The
number representation varies depending on the resolution. Therefore, make
sure that you are always within the permissible limits when specifying val-
ues. Please take note of the following table:
Resolution Lies in the Range ... ..then Following Values are Possible...
0.1
m
/
increment
to 1
m
/
increment
–100000.000 to 100000.000 mm
1
m
/
increment
(inclusive) to
1000
m
/
increment
–1000000.000 to 1000000.000 mm
The resolution is calculated as shown in the following table:
Incremental Encoders Absolute Encoders
Input values Displacement per encoder
rev.
Increments per encoder rev.
Pulse evaluation: Quadruple
Displacement per encoder
rev.
Increments per encoder rev.
Calculation
RES +
Displacement
encoder rev.
4·
Increments
encoder rev.
RES +
Displacement
encoder rev.
Increments
encoder rev.
RES = Resolution
With the internal computations the results are rounded according to mathe-
matical rules.
Definition
Relationship
between Travel
Range and
Resolution
Calculating the
Resolution
Rounding of the
Values
Machine Data and Increments
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