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10.7 Executing "Length measurement and edge detection"
FM 352 electronic cam controller
118 Operating Instructions, 05/2011, A5E01071724-03
Data used in the parameter DB
Address Name Type Start
value
Comment
4.0 EDGEDIST DINT L#0 Minimum edge distance for edge detection
Range: 0 ... 1 000 000 000 µm
The minimum edge distance is used to define a range after the start of a measurement is detected
with an edge detection. The measurement will be discarded if the measuring operation ends within
this range.
The start of the measurement is not signaled unless the minimum edge distance has been traveled.
Conditions of length measurement
● The CPU program requires an interval of sufficient length between the off and on edges
at input I1 in order to be able to evaluate the result of the measurement before a new
measurement is triggered.
● The minimum interval between the positive and negative edges at input I1 and between
the negative edge and the next positive edge at input I1 must be greater than 2 ms.
Faulty measurement
FM 352 returns the length value -1 for the length when it detects a faulty measurement /
edge detection.
A "length measurement" or "edge detection" may only perform up to 126 zero transitions in
one direction. The FM 352 reports a faulty "length measurement" or "edge detection" if it
detects more than 126 zero transitions in one direction, regardless of whether or not it then
detects any zero transitions in the opposite direction. The zero transition represents the
rotary axis transition from the end of rotary axis value to 0, and vice versa.
A length measurement is also considered faulty if:
● the length measured at a rotary axis is greater than 2
31
.
● the on and off edges are detected simultaneously by FM 352 (for example, caused by
switch bounce).
This event can be signaled as a hardware interrupt.
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