I
6. LOADING AND INSTALLATION
MELSEC-A
(3) Power consumption of
output
circuits (with an average
number
of
points
switched on)
WOUT
= lout x Vdrop x average
number
of
outputs
on at one time
(W)
where, lout
=
output
current (actual operating current) (A)
Vdrop = voltage
dropped
across each
output
load (V)
(4) Power consumption of
input
circuits (with an average
number
of points
switched on)
WIN
= liN X E x average
number
of
inputs
on at
one
time (W)
Where, liN
~
input
current (effective value
for
AC) (A)
E =
input
voltage (actual operating voltage) (V)
(5) Power consumption of
the
special function
unit
power
supply
is ex-
pressed as:
Ws =
124v
x
24
+
1100V
x
100
(W)
The sum of
the
above values is
the
power
consumption
of
the
entire PC
system.
W=Wpw
+
W24V
+
WOUT
+
WIN
+ Ws (W)
Further calculations are necessary to
work
out
the
power
dissipated
by
the
other
equipment
in
the
panel.
Generally temperature rise in
the
panel is expressed as;
where, W :
power
consumption of
the
entire PC system
(obtained as above)
A panel inside surface area (m
2)
U 6 if
the
panel temperature is controlled by a fan, etc.
4 if panel: air is not circulated.
POINTI
Fans, heat exchangers of cooling units must be installed if
the
panel
temperature is likely to exceed 55°C.
Fans
should
be fitted with suitable filters and guards.
6-3
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