Surges and spikes on datalines can fry your communications boards and corrupt data. Surge Suppressors divert excess energy away from the port being protected into a ground connection. The operation of these devices relies on a high quality ground connection in order to safely shunt away unwanted energy.
Shunting harmful currents to ground before they reach the data port is the job of components such as Transient Voltage Suppressors (TVS), Metal Oxide Varistors (MOV) or gas discharge tubes. These devices all work by turning on at a set voltage. Once the clamp voltage has been exceeded, the devices provide a low impedance connection between terminals. These shunting devices are most often installed from each data line to the local earth ground, and should be selected to begin conducting current at a voltage as close as possible above the system's normal communications level. For RS-422 and RS-485 systems, the voltage rating selected is typically 5 - 7 volts, in RS-232 systems 12 - 15 volt devices are appropriate. These devices typically add some capacitive load to the data lines, similar to adding additional cable to the system. The effect of this is that the maximum cable length will be shorter and the maximum baud rate is often slower when transient suppresion is used. These factors should be taken into consideration when designing systems.
Surge suppressors must be installed as close to the port to be protected as possible, and must have an extremely low impedance connection to the local earth ground of the unit being protected. Interworld Electronics can supply a range of communications boards that include Transient Surge Suppressors on board. Including the transient protection on the board insures a low impedance shunt path for excess energy as well as a ground reference at the same potential as the host system. Available products include PCI Serial Communications cards, USB to Serial Communications converters and Ethernet Serial Device Servers with built in Transient Surge Suppressors.
When protection from ground potential differences as well as transient voltage spikes is required Optically Isolated Products should be considered.
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Serial Port Surge Suppression
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