20
Example 2: When 16 IRAs are installed
Conditions: Assuming the distance from IRCU/IRCUDAN to IRD1 is 10 m, the distance from IRD1 to
IRD2 is 10 m, and the distance from IRD2 to IRA is 20 m. When 5C-2V coaxial cable is used.
1) Calculating maximum allowable loss
①
Attenuation from IRCU/IRCUDAN to IRD1 = 2.7 dB × (10 m/100 m) = 0.27 dB
②
Attenuation from IRD1 and 2 = 2.7 dB × (10 m/100 m) = 0.27 dB
③
Attenuation from IRD2 to IRA = 2.7 dB × (20 m/100 m) = 0.54 dB
④
Loss from IRD1 and 2 = 4 dB + 4 dB = 8 dB
The total attenuation from the cables and loss from the IRDs is 9.08 dB (0.27 dB + 0.27 dB + 0.54 dB +
8 dB), which is less than the maximum allowable loss (15 dB).
2) Calculating maximum allowable drop in voltage
①
Voltage drop from IRCU/IRCUDAN to IRD1
= 3.59 Ω × (10 m/100 m) × 0.09 A × 4 = 0.129 V
②
Voltage drop of IRD1 = 0.5 Ω × 0.09 A × 4 = 0.18 V
③
Voltage drop between IRD1 and 2 = 3.59 Ω × (10 m/100 m) × 0.09 A × 2 = 0.064 V
④
Voltage drop of IRD2 = 0.5 Ω × 0.18 A = 0.09 V
⑤
Voltage drop between IRD2 and IRA = 3.59 Ω × (20 m/100 m) × 0.09 A = 0.064 V
The total voltage drop is 0.527 V (0.129 V + 0.18 V + 0.064 V + 0.09 V + 0.064 V), which is less than the
maximum allowable voltage drop (3 V).
IRA
IRCU/
IRCUDAN
IRD2
IRD1
10 m
10 m
20 m
