VTI Instruments Metek EX1202 - Page 156

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156 Appendix B
FIGURE B-1: BACKPLANE POWER SEGMENTS IN THE EX12X8
When power requirements are calculated for these mainframes, the calculations should consider
each backplane segment as an independent power system. The total power useable (P
USEABLE
) on a
segment is defined by the Useable Power specification for the mainframe being used. As the
EX12x8 has a power supply dedicated to generating the 3.3 V output, no efficiency correction is
required, making the conditions required somewhat simplified compared to the EX12x6:
1) P
24V
+ P
5V
≤ P
USEABLE
2) P
24V
≤ 84 W
3) P
5V
≤ 75 W
4) P
3.3V
≤ 49.5 W
5) No rail can exceed the maximum current per rail. Particular attention should be paid to the
24 V rail.
To illustrate, the same cards will be used as in the previous example and they will be installed in
slots 1, 2, and 3 of an EX1268.
P
24V
= 24 V x [I
24V (EX1200-3608)
+ I
24V (EX1200-2001)
+ I
24V (EX1200-3048)
]
P
24V
= 24 V x (1.4 A + 0 A + 0 A)
P
24V
= 33.6 W
P
5V
= 5 V x [I
5V (EX1200-3608)
+ I
5V (EX1200-2001)
+ I
5V (EX1200-3048)
]
P
5V
= 5 V x (1.000 A + 0.454 A + 0.234 A)
P
5V
= 8.44 W
P
3.3V
= 3.3 V x [I
3.3V (EX1200-3608)
+ I
3.3V (EX1200-2001)
+ I
3.3V (EX1200-3048)
] / 80% efficiency
P
3.3V
= 3.3 V x (0.300 A + 0.131 A + 0.129 A)
P
3.3V
= 1.848 W
For this EX1268, the remaining three slots have 77.96 W available for plug-in modules to use on
the 5 V and 24 V rails, while 47.652 W remain on the 3.3 V rail on the remaining thirteen slots of
the mainframe.