56 GE INFORMATION D20E ETHERNET I/O MODULE INSTRUCTION MANUAL
CHAPTER 3: CONFIGURING THE D20E FIRMWARE
COS and SOE
The digital input state change report can be set to report:
• With a time tag (SOE mode) or
• Without time tag (COS mode).
In SOE mode, point state changes are marked with a time tag from the local device; this
time tag is then passed to the mapped server (e.g., DNP3) message accordingly.
Two Level Filtering
The D20E module uses two-level filtering to ensure that digital input reporting is stable:
• The first level of filtering is performed by the Debounce Filter and
• The second level of filtering is performed by a Chatter Filter.
In order to successfully report a digital status change, the input signal must pass through
both filters. See the Debounce and Chatter Filter process in
Figure 9.
Figure 9: Debounce and chatter filter process
Debounce filter period
The debounce filter period is the length of time that a digital input value has to be set
stable before the application reports the actual state change. The filter time eliminates
debounces and short disturbances on a digital input. The filter time is set individually for
each digital input point.
Chatter filter (oscillation suppression)
The oscillation suppression is used to block point changes and alarms for the overall
system if a digital input starts oscillating. A digital input is regarded as oscillating if the
number of valid status changes during a 1 second period is greater than the set value of
the input oscillation (On Trigger); if oscillating, the digital input is blocked (status is invalid)
and an events alarm is generated. The state of the input does not change when the point is
blocked and the point’s state depends on the condition before blocking.
The digital input is regarded as non-oscillating if the number of valid status changes during
a period of time (e.g., one second) is less than the set recovery value of the input oscillation
level (Off Hysteresis). When the input returns to a non-oscillating state, the digital input is
deblocked (status is valid) and events can be reported.
The oscillation recovery (Off Hysteresis) must be set lower than the oscillation On Trigger
level to enable the input to be restored from oscillation.
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