Model 268 Application Notes

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.


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