Apollo AAN-4, Руководство по оборудованию

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18 System Wiring
© 2011 Apollo Security Inc.
3.2.3 Safety (Earth) Ground
Safety ground is part of the AC power system. To avoid ground loop current, there must be only ONE point
at which the safety ground connects to the DC ground.
The RS-485 signal ground must be isolated from the safety ground. This means that the RS-485 cable shield
drain wire must be insulated at connection points so that it will NOT accidentally short circuit to the conduit in
instances where the conduit is connected to the safety ground. (See Figure 117)
Please check the applicable regulations and legislation in your country prior to installing the AAN-4 controller
and other Apollo products. In the US, the National Electrical Code, as well as other safety regulations,
require that all equipment chassis and/or enclosures be grounded in order to prevent electrical shock
hazards. Each device must have a green wire safety ground. The function of the green wire safety ground is
to provide a redundant path for fault currents and to insure that the circuit breaker will open in the event of a
fault. In addition, grounding the enclosure provides a path for ESD dissipation, thus protecting sensitive
electronic devices. (See Figures 115 and 116)
3.2.4 Grounding System
A grounding system can be viewed as two subsystems: the DC system and the Ground System. The DC
system consists of all interconnected power supply returns, DC distribution wiring, and load devices. The
principal function of the DC system is to provide signal reference for communication. The Ground System
consists of all chassis grounds for power supplies and other devices, safety grounds, and AC grounds.
Ground connection should be made to avoid ground loop problems. (See Figure 115)
Ideally, there should be ONLY ONE ground return point in a power supply system. In a system with a PC
(personal computer), it is likely that the PC already provides the DC Ground connection to the Ground
System (earth ground). Care must be taken NOT to create more ground connections. In systems with
multiple PCs communicating to Apollo Hardware via direct connection, the ground potential must be the
same for inter-connection, or some form of isolation must be provided.
3.2.5 Grounding Potential Difference Checks Before Connecting
Before a device is connected to an RS-485 subsystem, it must be checked for ground fault. Uncorrected
ground fault can damage all devices connected to the RS-485 communication line.
To check if there is ground fault for a new unit, follow the steps below (See Figures 105, 113, 115, 116 and
120):
1. Apply power to all devices already successfully connected to the RS-485 line.
2. Power up the new unit, but DO NOT connect it to the RS-485 line.
3. Connect the signal ground (SG) of the RS-485 line through a 10k limiting resistor.
4. Measure the AC and DC voltage across the resistor. There should NOT be more than 1 volt across the
resistor. Otherwise find and clear the fault.
5. Connect the new unit to the RS-485 line only if no ground fault is found.
3.3 Host Communication Connection
The connection from the AAN-4 to the programming host (PC) is used for programming the panel and then
monitoring the status of the system. Once a connection is established, the host software communicates with
the panel and transmits the necessary configuration information. Once this is established, the host and panel
will maintain a constant communication until it is terminated by the host. While connected, the controller will
send events in real-time after a request from the host. The controller will not send information to the host
unless a request is received. These events will be ‘buffered’ in the memory of the controller until the host is
ready to receive. Thus, all system events are protected and will not be sent to a host that is not ‘listening’,
therefore losing events.