10
LOADING AND INSTALLATION
10.1 Calculating Heat Generation of PLC
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10.1 Calculating Heat Generation of PLC
The ambient temperature inside the panel storing the PLC must be suppressed to an
ambient temperature of 55
or less, which is specified for the PLC.
For the design of a heat releasing panel, it is necessary to know the average power
consumption (heating value) of the devices and instruments stored inside.
Here the method of obtaining the average power consumption of the PLC system is
described.
From the power consumption, calculate a rise in ambient temperature inside the panel.
The power consuming parts of the PLC are roughly classified into six blocks as shown
below.
(1) Power consumption of power supply module
The power conversion efficiency of the power supply module is approx. 70 %, while
30 % of the output power is consumed as heat. As a result, 3/7 of the output power is
the power consumption.
Therefore the calculation formula is as follows.
I
5V
: Current consumption of logic 5 VDC circuit of each module
(2) Total power consumption for 5VDC logic circuits of all modules
(including CPU module)
The power consumption of the 5 VDC output circuit section of the power supply
module is the power consumption of each module (including the current consumption
of the base unit).
W
5V
= I
5V
5 (W)
The total of the power consumption values calculated for each block becomes the power
consumption of the overall sequencer system.
From this overall power consumption (W), calculate the heating value and a rise in
ambient temperature inside the panel.
The outline of the calculation formula for a rise in ambient temperature inside the panel is
shown below.
W : Power consumption of overall sequencer system (value obtained above)
A : Surface area inside the panel
U : When the ambient temperature inside the panel is uniformed by a fan........ 6
When air inside the panel is not circulated ................................................... 4
How to calculate average power consumption
W = W
PW
+W
5V
PW
=
3
7
×(I5v×5) (W)
W
=
C
T
UA
W
