GE 90-30 PLC Series Installation And Hardware Manual page 392

Discrete Input Module Example:
The "Specifications" table for the IC693MDL240 16-Point Discrete 120 VAC Input Module in the
Series 90-30 PLC I/O Module Specification Manual, GFK-0898, gives the following information:
Use this value for all of the input calculations for this module.
In this example, eight of the Input Module's points are used for switches that, for normal operation,
stay on (closed) 100% of the time. These include the Emergency Stop, Over Temperature, Lube
Pressure OK, and similar switches.
Use the formula Average Power Dissipation = Input Voltage x Input Current (in Amps) x Percent
(expressed as a decimal) of on-time:
Then multiply this result by 8:
Also in this example, two input points on this 16-point module are for the Control On and Pump
Start pushbuttons. Under normal conditions, these pushbuttons are only pressed once per day for
about one second – just long enough to start up the control and pump. Therefore, their effect on
our power calculation is negligible and we will assume a power dissipation of zero for them:
For the remaining six inputs of our sixteen point module, it is estimated that they will be on for an
average of 20% of the time. So the following calculation is made for these six inputs:
Using the formula of Average Power Dissipation = Input Voltage x Input Current (in Amps) x
Percent (expressed as a decimal) of on-time:
Then multiply this result by 6:
Finally, adding up the individual calculations, we get:
GFK-0356Q Appendix F Calculating Series 90-30 Heat Dissipation
Repeat for all inputs on the module. To save time, you could determine if several inputs
were similar in current draw and on-time so that you would only have to make their
calculation once.
Repeat these calculations for all Discrete Input modules in the rack.
Input Current: 12 mA (typical) at rated voltage
120 x .012 x 1.0 = 1.44 watts per input
1.44 watts x 8 inputs = 11.52 watts total for the 8 inputs
0.0 watts total for 2 inputs
120 x .012 x 0.20 = 0.288 watts per input
0.288 watts x 6 inputs = 1.728 watts total for the 6 inputs
11.52 + 0.0 + 1.728 = 13.248 watts for the module's total input calculation
F
F-5