Siemens S7-300 Operating Instructions Manual page 139

Pulses
The FM 352 evaluates all 4 edges of the A and B signals (see diagram) in each increment
(quadruple evaluation).
1 increment (encoder default) = 4 pulses (FM evaluation)
Reaction times
The FM 352 has the following reaction times for connected incremental encoders:
Minimum reaction time = cam cycle time + switching time of the connected switching
elements
Maximum reaction time = 2 x cam cycle time + switching time of the connected switching
elements
Example
Example of the min./max. reaction time with 16 cams available:
● Cam cycle time: approx. 20 µs
● Switching time of the hardware: approx. 150 µs
Minimum reaction time = 20 µs + 150 µs = 170 µs
Maximum reaction time = 2 x 20 µs + 150 µs = 190 µs
Note
You can compensate the reaction time by assigning the cam parameters accordingly or
using dynamic adjustment.
Flat gain
The flat gain is equivalent to the difference between the min./max. reaction time. For
incremental encoders this is:
Flat gain = cam cycle time
Note
If the switching time of the FM 352 hardware and of the connected switching elements can
be disregarded, reliable cam activation is always ensured if the cam is longer than the
distance covered within the cam cycle time.
FM 352 electronic cam controller
Operating Instructions, 05/2011, A5E01071724-03
Encoders
11.1 Incremental encoders
139