Omega Vehicle Security ISA RS-422 - Manual (Page 20)

Appendix D - Ground Loop Phenomenon
OMG-ULTRA-SIO Page 16
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 OMG-ULTRA-SIO in a RS-485 network, care should be
taken that both ends of the network are not isolated from ground (see Figure 12).
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
Ultra SIO
Non
Isolated
Ultra SIO
Figure 11 - OMG-ULTRA-SIO cabling example