Siemens SIMATIC ET 200S Manual page 326

Digital Electronic Modules
Flutter monitoring
Flutter monitoring is a process control function for digital input signals. It detects
and reports unusual process control signal patterns, for example, frequent
fluctuation of the "0" and "1" input signal. Such signal activities are an indication
that a sensor is defective or that the process is unstable.
Enabling flutter monitoring
Enable flutter monitoring by setting the number of signal transitions to a value other
than "0."
Detection of unusual signal patterns
A configurable monitoring window is available for each input channel. The
monitoring window is started at the first transition of the input signal. If the number
of input signal transitions within the monitoring window exceeds the set number,
the system detects a flutter error. If a flutter error is not detected within the
monitoring window, the monitoring window is started again at the next signal
change.
Reporting a Flutter Error
If a flutter error occurs, the current signal state is entered in the process image and
the value status of the signal is set to "invalid". The diagnostic information "flutter
error" is entered and a diagnostic interrupt entering the state is triggered.
You must evaluate and process the value status and the diagnostic information in
the user program.
Resetting a Flutter Error
If no further fluttering of the input signal is detected during the triple monitoring
window, the diagnostic entry is removed and an outgoing diagnostic interrupt is
triggered. The value status of the current signal in the process image is set to
"valid".
11-6
ET 200S Distributed I/O System
EWA-4NEB 780602402-12