Network Communications—N2 Communications Bus
13
•
The maximum distance between two fiber modems is 2012 m
(6600 ft). If your application requires lengths beyond 2012 m (6600 ft),
contact S.I. Tech for information about their “high power” option.
•
You may also use optical fiber on the N2 Bus. (A pair of fiber modems
is required for conversion.) Duplex optical fiber is needed, either
50 (3.0 dB/km), 62.5 (4.0 dB/km), or 100 (5.0 dB/km) micrometers.
The 62.5 size is preferred.
Terminations
Each N2 device should be properly terminated as described in the
Setting
Terminations
section.
Over time, the control needs of a building may require modifications to the
N2 Bus installation. For details, refer to the
Modifying the N2 Bus
Installation
section later in this document.
With the introduction of the NCM200 and NCM300, a larger allocated
memory capacity allows for increased database sizes per NCM. This
means you can add more elements to your system.
There is probably enough allocated memory for your database, but the
N2 Bus does have a finite bandwidth. Excessive traffic could slow down
the system despite adequate memory. Use generally accepted estimating
practices, then follow the guidelines below to maximize N2 operation.
Lab and Central Plant Controller (LCP) and DX9100 devices function
differently than other Metasys controllers. Therefore, if you use these
devices and have throughput problems, follow the suggestions below to
ensure that Metasys operates with maximum efficiency.
•
Priority One
--Reduce the number of commands going to LCP or
DX9100 devices from GPL processes. If a process has 30 or more
consecutive commands or if the process is executed faster than every
20 seconds, you either:
-
increase the period length of the process or make it run on triggers
only, or
-
place delays between consecutive commands
•
Use Metasys Release 6.00 or later software to take advantage of
improvements in LCP/DX9100 message processing.
•
Reduce online polling by reducing the polling priority to Level 3 for all
devices on the N2 network.
•
Get offline devices back online as soon as possible. Refer to the
device’s technical bulletin in the
Metasys Network Technical Manual
(FAN 636)
for details.
•
Reduce the number of Analog Data (AD) and Binary Data (BD)
associated input points.
System
Expansion
Maximizing
Your System’s
Efficiency