Device Signal Jitter; Fault Isolation; Short Circuit Current Limitation (Static Fault Protection); Spur Contact Bounce Protection (Dynamic Fault Protection) - Pepperl+Fuchs R2-SP-IC Series Manual

Segment Protector
Operation
The monitoring alarm setpoints are:
Signal level 'Maintenance required':
Signal level 'Out of Specification':
Where Upp is the peak-to-peak signal level
5.2.2

Device Signal Jitter

The device signal jitter is the deviation from the ideal timing of the communication signal. In
fieldbus technology, jitter is the deviation of the ideal zero crossing point of the transmitted
signal curve during the nominal bit duration. This deviation is measured in relation to the
previous zero crossing, i. e., the reference event.
The device signal jitter is the most important parameter to monitor where the noise can
influence the signal.
The monitoring alarm setpoints are:
Jitter level "Maintenance required":
Jitter level "Out of Specification":
Where t is the jitter error in time
5.3

Fault Isolation

5.3.1

Short Circuit Current Limitation (Static Fault Protection)

The spur short circuit current limitation is designed to protect the entire segment from failing by
limiting the spur current from a direct short circuit (static protection). If the short circuit current
condition exceeds a specified period, the spur is automatically isolated from the trunk, i. e., it
does no longer receive any current.
5.3.2

Spur Contact Bounce Protection (Dynamic Fault Protection)

Periodic or intermittent changes in the current drawn throughout a segment can cause
continuous communication failures up to a point where the segment fails. Changes in the spur
current can occur during connection and disconnection of the spur wires or due to fractured or
loose wires under vibration.
Conventional spur protection is only designed to protect the segment by limiting the spur
current from a direct short circuit (static protection). It does not protect the segment from
periodic or intermittent low-level changes in the segment current (dynamic protection).
Under vibration, insufficiently attached, fractured, or loose fieldbus wires keep connecting and
disconnecting to the attached field device load. Because the spur is connected to one field
device, the current does normally not increase to a value that exceeds the short circuit current.
Such intermittent current disturbances are converted into corresponding voltage effects on the
trunk. This could cause a temporary or total loss of communication, even leading to the loss of
the segment.
The Pepperl+Fuchs Spur Contact Bounce Protection isolates a faulty spur from the segment to
prevent segment failures caused by intermittent faults that are not detected by conventional
spur protection device couplers.
5.3.3 Progressive Spur Short Circuit Current Limitation (Creeping Fault
Protection)
Conventional spur protection circuits are designed to prevent segment failures during fast
current changes above the rated short circuit current (direct short circuits).
Upp  300 mV or Upp  1200 mV
Upp  200 mV or Upp  1300 mV
t  3.5 sec and t  5 sec
t  5 sec
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