14
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 AIM-1/2SL
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
Communication Connection
The serial connection from the AIM-1/2SL to controller devices is used to collect requests and information
from the AIM-1/2SL to the controller and for the controller to transmit responses to these messages. The
AIM-1/2SL does not originate communication on the device communication lines but waits for a poll from the
controller and then establishes communication for configuration. The first communication from the controller
establishes the presence and proper functioning of the field device, and then the configuration is
subsequently sent in the following polling cycles. This polling is done many times a second, with the exact
parameters for polling (intervals, timeout, retries) being set by the host software.
Summary of Contents for AIM-1SL
Page 6: ...Part Introduction I ...
Page 9: ...Part Hardware Layout II ...
Page 17: ...Part System Wiring III ...
Page 37: ...Part Troubleshooting IV ...
Page 40: ...Part Specifications V ...
Page 42: ...Part Supplemental Figures VI ...
Page 43: ...38 Supplemental Figures 2011 Apollo Security Inc 6 Supplemental Figures ...
Page 44: ...39 AIM 1SL AIM 2SL Hardware Manual 2011 Apollo Security Inc ...
Page 45: ...40 Supplemental Figures 2011 Apollo Security Inc ...
Page 46: ...41 AIM 1SL AIM 2SL Hardware Manual 2011 Apollo Security Inc ...
Page 47: ...42 Supplemental Figures 2011 Apollo Security Inc ...
Page 48: ...43 AIM 1SL AIM 2SL Hardware Manual 2011 Apollo Security Inc ...
Page 49: ...Part Table of Figures VII ...
Page 51: ...Part Revision History VIII ...