Panasonic Firetracker FT1020G3 CIE, Техническое и программное руководство

Страница: 174 / 192

Technical/Programming Manual
FT1020G3 Rev 2.2.1
171
Therefore, the maximum allowable distance
𝐷 =
𝑅
𝑚𝑎𝑥
2𝑅
𝑢
=
42.3
2(0.0119)
= 1777 𝑚
If the temperature was raised to 80

C, we would expect that the resistance will also
increase. The relationship between resistance and temperature is given by,
𝑅 = 𝑅
𝑟𝑒𝑓
[1 + 𝛼
𝑐𝑢
(𝑇 − 𝑇
𝑟𝑒𝑓
)]
Where,
R = Resistance per unit
R
ref
=
Resistance per unit at a reference temperature
Coefficient of copper
𝛼
𝑐𝑢
= 0.00323
T = Actual temperature
T
ref
= Reference temperature
Hence, calculating for this gives:
𝑅 = 0.0119[1 + 0.00323(80 − 20)] Ω/𝑚 = 0.0142 Ω/𝑚
Therefore, the new distance would be:
𝐷 =
42.3
2(0.0142)
= 1489 𝑚
Figure 56 COM Loop Current Consumtion vs. Cable Length
The total COM loop unit current consumption is increased as the number of units are added
to a loop. Refer to “Current consumption” page 174 as details are given as to how much
current is consumed by each unit as they are added to the loop.
Use the FT1020G3
400
600
800
1000
1200
1400
1600
1800
0 50 100 150 200 250 300 350
Ca
bl
e
Le
ng
th
(M
et
er
s)
Total COM loop unit current consumption (mA)
Total COM Loop Unit
Current Consumption
(mA)
1.50mm 2 Cable .
11.9Ω/Km
Maximum Cable Length