Pepperl+Fuchs HD2-DM-A Manual page 145

Advanced Diagnostics
Appendix
8 Appendix
8.1 Measured Values / Parameters
8.1.1 Board Type
Board Type Detection
The type of the board on which the HD2-DM-A is installed is detected.
Board Redundancy Detection
Detects whether the HD2-DM-A is installed on a redundant board or not.
8.1.2 Communication Active
Communication activity is detected if any valid frames (Preamble, SOF, EOF) are detected.
Loss of communication is detected if no valid signal is recognized for at least 4 seconds.
8.1.3 Current
The current supplied to the segment is measured.
Type
Precision
Measuring range
8.1.4 Unbalance
The parameter detects unbalance between signal wire and ground (shield). This measurement
signals an earth unbalance. This is the case if a segment that belongs to the same isolation
group has a DC earth unbalance, e. g., a short circuit from a signal line to shield.
Type
Precision
Measuring range
Definition
Unbalance is the result of a capacitive or resistive connection between the fieldbus signal wires
and ground (cable shield).
Possible Causes
Miswiring/incorrect installation
In the installation scenario illustrated below, several devices are installed incorrectly. On each
of the independent segments, one device is wired with the negative data line tied to the shield
while the shield is tied to earth ground.
Device influence: In order to increase electromagnetic compatibility stability, some plants
modify their fieldbus devices with asymmetric capacitive connections between shield and their
+ or - fieldbus line. If such fieldbus devices are connected to the plant, they influence the bal-
ance of the specific field device or the entire segment.
Wire damage: A wire damaged through external influences can also cause unbalance if there
is a short circuit between a fieldbus line and the cable shield.
144
Values
+/- 5%
0 ... 6.5 A (depends on the motherboard)
Values
1%
-100% (short against - wire)
to
+100% (short against + wire)
see Figure 8.1 on page 145: