The SD-8 is a solid state electronic device designed to monitor 8 different alarm conditions. The SD-8 will monitor either normally open or normally closed sustained dry contacts. Each alarm condition which is to be monitored by the SD-8 should have a set of contacts which either close or open upon an alarm condition. A pair of wires is connected from this alarm contact to the SD-8 barrier terminal located inside the Polycarbonate enclosure. The barrier terminal uses two individual screw down lugs for each channel. It is unimportant which one of the wires from the alarm contact is connected to which alarm terminal. It is important that the pair be connected to the corresponding pair of terminal lugs assigned to the channel being monitored. This pair of wires from the alarm contact will not have any current or voltage on the pair generated from the alarm source. The SD-8 generates a low voltage signal which uses the pair of wires. When the circuit is in alarm (in the case of a normally open contact) the low voltage generated by the SD-8 is sent out on one wire and is returned on the other wire. This will cause the LED associated with the alarm channel which is now in alarm to turn on. Conversely if the contact type was of the normally closed type the LED on the alarm board would be on all of the time and an alarm condition would extinguish the LED.
The alarm section occupies a portion of the main board. This section is located on the top circuit board towards the lower center of the SD-8. Each of the eight LEDs will illuminate when the corresponding circuit is completed and will extinguish when the circuit is open.
The source of the low voltage current used to monitor the alarms is generated from the 12 volt power supply unit located on the same board. The onboard resistors act as current limiting devices for the circuit. This power circuit is protected against direct shorts which could destroy other components. The power supply unit is protected by an internal "crow bar" feature which protects the system. The SD-8 uses a unique approach to limiting the transient signals which are generated from the outside world and which would be transferred to the main board. This is done with opto couplers. An analogy would be a "magic ditch" separating the outside world from the main board. This "magic ditch" will not allow any high current to travel from one side to the other. On the side which is closed to the outside world, a person stands and waits for a signal from the outside contacts. The other side is where the microprocessor and other circuitry reside. The person on the side which is closest to the world has a flood light. When the alarm condition is activated the person on the side with the flood light turns on the light and shines across the "magic ditch" to the second person. The second person on the side of the main board then presses a button and sends a small controlled signal to the main board advising the main board that there is an alarm. This way no transients or high voltage can get to the main processor board. This will virtually eliminate the damage to the microprocessor from outside power sources.
The main board is easily removed if required by removal of screws and removing the board from the enclosure.
There are several additional buttons and switches which are on the SD-8 which will be covered now.
ELECTRICAL REQUIREMENTS
The SD-8 requires PRIVATE CIRCUIT 115 v a/c 60 cycle single phase line to be connected near the external side of the enclosure. This connector should be marked 115 volts A/C. A pair of number 14 stranded copper wires with ground is supplied by the customer. The source of the wire is connected to a private circuit (not shared by another user) which is fused with a 15 amp breaker at the source. A single pair of wires is connected from the 9 V D/C transformer to the SD-8 dialer. The 12 V D/C power supply is plugged into the 15 amp duplex receptacle. The incoming wires to the power supply are polarity sensitive and should be attached as shipped from the factory. The positive (+) is connected to the top pin of JP-3 and is a red wire. The negative (-) is connected to the second pin of JP-2 and is a black wire. The customer will provide a ground wire to a good known ground to insure that the sidactor has a good path to ground. The sidactor dissipates hi voltage on the incoming telephone line during a high voltage condition.
TELEPHONE SERVICE
Telephone service is required for the SD-8 to call out and notify personnel of the alarm conditions. The type service required is the same type telephone service you would have in you home or office. Leased or dedicated telephone circuits are not required and will not work if installed. Terminate the telephone line in the supplied telephone terminal block. This requires a red wire and a green wire. The TIP and RING pair and ground is all that is required for installation of the phone service. Each SD-8 is shipped with two telephone cords. One cord has a lugged and 4 pin modular jack end, the other cord has a 4-pin modular jack on each end for connection into the telephone service.
Telephone voltage surges are diminished by a sidactor which is capable of absorbing 300 to 600 volts without damage to the component. This provides for protection on the telephone lines. This must be connected to a ground.
Updated 3/98