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Earth Ground
VSI-Pro Max POS / Cash Register Interface
CONNECTIONS
Grounding and Isolation
The VSI-Pro Max has an isolated internal signal/power ground from the case or chassis ground. Therefore maintain-
ing this isolation will insure proper surge and lightning suppression when the chassis grounded properly.
Video Surge / Lightning Protection
The VSI-Pro Max has an internal Gas Discharge Surge Suppressor on the video input. This enables high input
surges to be suppressed so not to damage the internal circuitry of the VSI-Pro Max. Voltage spikes between video
signal and video ground will be clamped and also between both of these signals and chassis ground. For this
suppression to be fully effective the “Earth” grounding lug between the two BNC connectors must be connected to a
solid and true earth ground. A good earth ground is a long metal rod into the ground 6’ or connection to copper water
pipes.
NOTE: If ground loops are in excess of 90 VAC to Earth or Signal ground the internal surge suppress make not be
effective and cause undo noise in the video. If this is the case do not use the chassis grounding lug for undo voltage
will be shorted through the suppression circuitry of the VSI-Pro Max.
Power Surge / Lightning Suppression
The VSI-Pro Max has MOV (Metal Oxide Varistors) across the power input to signal ground and from both of these
signal to chassis ground clamping at 18VDC. For this suppression to be fully effective the “Earth” grounding lug
between the two BNC connectors must be connected to a solid and true earth ground. A good earth ground is a long
metal rod into the ground 6’ or connection to copper water pipes.
RS-232 DB9F Shielding
The shield of the DB9 RS-232 connector also connects to chassis ground. Therefore this shield should not be
connected to any signal ground of any RS-232 signal or power signal. If for some reason the source or destination
devices have internal connections from signal ground to the shield then the shield should not be connected on VSI-
Pro Max end to maintain signal ground and earth ground isolation. Proper shielding of RS-232 signals will extend the
length of wiring especially at high data rates and eliminate noise being coupled into the either a source or destination
device by surrounding EMI or RFI generated by other equipment within the installation.
Figure 5 : VSI-Pro Max Earth Grounding Connection