Model 8381 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 that 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-422 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 8381 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. Isolation is provided while allowing full duplex communications at a data transmission rate of 115.2 KBPS between the RS-422 interfaces. The needed data transmission link is realized and ground loop currents are suppressed. This particular product provides isolation while even allowing the desired RS-422 link to be extended to 1 km.

Furthermore, the Model 8381 is DIN Rail mounted. This is particularly convenient for this factory floor application.

DIN Rail is a cabling system that was developed for factory automation and is now available for computer room use. The system is very simple and straightforward. It uses a steel channel called a DIN Rail. The rail has slotted holes for mounting. The Rail is normally mounted in a horizontal position. DIN Rail products are then placed in the Rail by snapping them into place after which the wiring is completed. DIN Rail mounting helps organize the computer room and prevents 'messy cabling' in the factory environment.
 

 

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