The DD-4 is a solid state electronic device designed to monitor 4 different alarm conditions. The DD-4 will monitor either normally open or normally closed sustained dry contacts. Each alarm condition which is to be monitored by the DD-4 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 DD-4 barrier terminal located inside the 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 DD-4 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 DD-4 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 main circuit board towards the lower center of the DD-4. The four LED's which will illuminate when the 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. The alarm board uses a unique approach to limiting the transients 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 DD-4 which will be covered now.
ELECTRICAL REQUIREMENTS
The DD-4 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 16 V A/C transformer to the dd-4 dialer. The 16 V A/C transformer is plugged into the 15 amp duplex receptical. The incoming wires to the transformer are polarity insensitive and can be connected to either lug of the transformer.
TELEPHONE SERVICE
Telephone service is required for the DD-4 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.
Updated 3/98