The electrical ground of a system is connected to earth and is therefore directly related to the electrical ground potential of the earth. Unfortunately the ground potential is not constant.

Powering equipment from different supplies at each end of a communication link will increase the systems susceptibility to differences in ground potential. There are also many transient events that can affect the ground potential. Switching heavy industrial equipment on and off can result in inductively induced power surges that can cause a difference in ground potential. Lightning strikes dump a large amount of current into the earth. Until this energy dissipates, the voltage level of the earth will vary greatly between two locations. The more physical area covered by the system, the more likely that differences in ground potential will exist.

Only Isolation is capable of protecting a system form large differences in ground potential. With isolation, two different grounds or reference voltages can exist on opposite sides of the isolation device without any current flowing through the device. By using a LED and a photosensitive transistor optical isolation only allows light to pass across the isolation barrier while voltages ranging from 500V to 4000V will be blocked.

The down side of isolation is that separate isolated power supplies are required on both sides of the optical barrier. Dual external supplies can be used or the additional supply may be a built in isolated DC-DC converter. In some circumstances dual Port Powered isolation devices can be used.

A simple and cost effective way to add isolation to an existing communication system is to employ an In-Line Isolator. Interworld Electronics has a wide range of RS-232 to RS-232 isolators, RS-232 to RS-422/485 isolated converters and RS-422/485 isolated repeaters. Our range includes:

QT232SPHI4: RS-232 Optical isolator, RS232 (DB25) to RS232 (DB25), port/external powered

QT422OISPR: Optically isolated RS-232 (DB25) to RS-422, (DB25), 4 wire full duplex, External Power Supply Included

QT485OT9L: Optically isolated, RS232 (DB9) to RS422/485 (Terminal Block), 4/2 wire full/half duplex, external powered

QT485OTLED: Optically isolated, RS232 (DB25) to RS422/485 (Terminal Block), 4/2 wire full/half duplex, LED display, external powered

QT485OP: Optically isolated Repeater, RS422/485 (DB9) to RS422/485 (Terminal Block), 4/2 wire full/half duplex, external power supply included

QT9SPOP2: RS-232 Optical isolator, RS232 (DB9) to RS232 (DB9), port powered

For More Information Contact Interworld Electronics

Next month we will take a look at Surge Suppression and the range of available products.

For More Information Contact Interworld Electronics