Impulse 7203 - Manual (Page 17)

Appendix D - Asynchronous Communications
Sealevel Systems ULTRA COMM+2I.PCI Page 14
Appendix D - Ground Loop Phenomenon
What is Ground Loop?
Ground loop Phenomenon occurs when two (or more) pieces of equipment are
connected together with a common ground and a different ground potential
exists at each location. This current can cause the connected equipment to
experience noise that in turn causes data transmission errors. In the extreme this
ground current can cause equipment malfunction or even destruction.
Cabling Recommendations
When connecting the ULTRA COMM+2I.PCI in a RS-485 network, care
should be taken that both ends of the network are not isolated from ground (see
Figure 8). This “floating” ground condition could cause the capacitive or
inductive coupling of voltages that will cause a break down in the DC to DC
converter circuit or in the opto-isolator circuit. This condition will cause data
errors and possibly destruction of the receiver circuit.
A B
Isolation
Barrier
DATA+
DATA-
Ground
Isolated
Adapter
Non
Isolated
Adapter
Figure 8 – ULTRA COMM+2I.PCI cabling example