WAGO-I/O-SYSTEM 750
Ground Fault Diagnostics 33
750-626/020-002 Power Supply Filter 24 VDC HI GF
Manual
Version 1.0.0
Figure 11: Ground Fault Diagnostics Functionality
The power supply filter with ground fault diagnostics detects a fault resistance
(ohmic) between the 24V field potential and the DIN-rail potential or the 0V field
potential and the DIN-rail potential. The internal test circuit of the power supply
filter is switched to the DIN-rail contact.
To use the field supply filter for ground fault diagnostics, the function must be
enabled. The user must set the “GFT” (Ground Fault Test) bit in the output
process image of the fieldbus coupler or controller. The field bus, PLC application
or WAGO-I/O-
CHECK
commissioning tool can be used for this purpose.
Connecting the ground fault diagnostics influences measurement of a ground
fault monitor operated in parallel because the internal resistance in the relevant
supply network or feed segment changes due to the internal resistance of the test
circuit.
The influence is greater, the more filter modules with ground fault diagnostics in
the relevant supply network or feed segment exist where a ground fault
diagnostics was enabled. Conversely, however, a ground fault monitor operating
in parallel also influences the ground fault diagnostics of the power supply filter
due to its internal resistance.
A ground fault against the +24V field or 0V field potential is reported by the power
supply filter via separate diagnostic information, as a pre-alarm and main alarm.
A ground fault is detected at a threshold of <=50 kΩ (typ.) and triggers a pre-
alarm. If the fault resistance falls below 25 kΩ (typ.), a main alarm sounds.
The test circuit of the power supply filter has a hysteresis behavior. To reset the
alarms, it is therefore necessary that the fault resistance assumes a
corresponding value above the respective threshold (“Technical Data” > “Ground
Fault Diagnostics”).