Hysteresis; Hysteresis With Incremental Or Pulse Encoder - Siemens SIMATIC ST-1500 Function Manual

The basics of counting, measurement and position detection
2.2 Basics of counting, measuring and position input (TM Count, TM PosInput, Compact CPU)
2.2.10

Hysteresis

2.2.10.1

Hysteresis with incremental or pulse encoder

Description
Hysteresis allows you to specify a range around the comparison values within which the
digital outputs are not to be switched again until the counter value has gone outside this
range.
Slight movements by the encoder can result in the counter value fluctuating around a certain
value. If a comparison value or a counting limit lies within this fluctuation range, the
corresponding digital output is switched on and off with corresponding frequency if hysteresis
is not used. Hysteresis prevents this unwanted switching, and configured hardware interrupts
when a comparison event occurs.
The hysteresis becomes active when the respective comparison value is reached by a count
pulse. If the counter value is set to the start value during an active hysteresis, the hysteresis
becomes inactive.
Regardless of the hysteresis value, the hysteresis range ends at the low/high counting limits.
Function principle
The figure below shows an example for the hysteresis with the following configuration:
● Setting of a digital output between comparison value and high counting limit
● Comparison value = 5
● Hysteresis = 0 or 2 (gray background)
Hysteresis is enabled when the counter value 5 is reached. When the hysteresis is active,
the comparison result remains unchanged. Hysteresis is disabled when the counter value 2
or 8 is reached.
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Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG