
A common problem in many data communications environments is the need
for an isolation capability.
The need for isolation arises because in many instances the equipment
being connected must be grounded at different points. Different grounds
imply different reference levels for voltages and this can lead to
inaccuracies in the physical quantities being measured by the different
instruments. It can also lead to the generation of currents between the
grounds- currents which attempt to equalize the ground voltage levels
and bring them into equilibrium. These 'ground currents' can damage
equipment and possibly hurt personnel handling the equipment. Isolation
provides a barrier between different ground points. This barrier does
not allow ground currents to be generated. Isolation allows equipment
being grounded at different points to be connected together without the
need to worry about inaccuracies or equipment/personnel damage due to
ground currents.
The illustration above shows a ready application where isolation is an
issue. A data acquisition system is installed on a factory floor and is
grounded to a point near where it is located. It sends data acquired to
a PC elsewhere in the factory which responds with control messages back
to the data acquisition system. The PC is grounded to a point near where
it is located. At both ends data is coming into and out of an RS-232
interface. Because of the separate grounds this full duplex
communication link is subject to ground loops. This can causes
inaccurate 'readings' of the data at either end of the link. This
problem is easily solved by placing the Model 268 isolator in the
communication link. This provides a barrier between the grounds. There
is effectively no electrical connection between the ground points at
either end of the link. Both can be used and ground loop currents are
suppressed.
|