Johnson Controls Metasys Intelligent Fire Network Technical Manual page 25

Determining the FN System Path Length
When using either fiber optic cable or twisted pair copper wire, the overall
FN system path length is influenced by the total number of MIB,
MIB-OWS, and repeater devices, as well as FN medium type. The length
is limited by various factors including the maximum response time (t
propagation delays in 3,000-ft segment (t
per MIB/repeater (t
m/r
The formula is as follows:
T=((t -t )/2)⋅k
max ta
L=(T-N⋅t )/(t
m/r 3k
Where:
N -
number of segments
t -
9548 microseconds
max
t -
20 microseconds
3k
t -
1.5 microseconds
m/r
t -
101.6 microseconds
ta
T -
maximum propagation one way
k -
0.85 (derating factor)
L -
total FN system path length
Overall Distance
(in feet)
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
0
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
Figure 4: Node vs. Medium Distance Limitations
), maximum propagation delay
3k
), and maximum turnaround time (t
/3000)
Total Number of Nodes/Repeaters
IFC Networking—Metasys Intelligent Fire Network
),
max
).
ta
graph
25