Relay Cards are actually Digital I/O Cards (Input / Output) and are normally used as an output device for controlling external devices such as access control barriers. It can also be used as a digital input device in bespoke systems to detect motion or vehicle presence in cases where it is imperative to capture an image of a vehicle that is not carrying a plate or when a vehicle has a severely damaged plate.The RPX-LIVE Software reads a plate as a vehicle approaches and can then automatically open a barrier, control red / green traffic lights or illuminate a static message sign such as “CAR PARK FULL” depending on the parameters set.
These cards are termed “Digital” because they contain small relays and will close or open a contact for a pre-determined length of time. For example, a standard entrance barrier has its control box that will normally trigger on a pulse width of 200ms. When used for controlling a Traffic Light the user may want the light displayed for say 7000ms (7 secs). Sometimes this feature is used to control a Red Traffic light if the ANPR system reads the plate and determines that the vehicle is unauthorised for some reason. The red light can then alert an external guard to the problem.
Relays can also be used to trigger audible external alarms and flashing beacons when a vehicle is in a wanted Hotlist. These signals can also be used as inputs to external site-wide alarm systems.