Campbell Scientific 9522B Iridium Satellite Modem and COM9522B Interface Modem - Manual (Page 32)

Appendix A. Sample Data Transfer Calculations
Power Calculation
When configuring a power supply (that is, solar panel and battery)
for a remote station, it is essential to design with the worst case
scenario in mind. This will help to ensure that the station will
perform as expected.
The power calculation for data transfer can be carried out now that the transfer
time is known. The modem has the following power consumption
characteristics:
- 0 mA when powered off
- 300 mA stand-by
- 800 mA transmit (2500 mA max)
The time slot for powering the modem must be long enough to allow for the
complete downloading of the datalogger’s data and connection times. Refer to
TABLE A-1 or make your own calculation based on the collection interval you
intend to use.
It is advisable to make the time slot longer than the minimum download time
required to allow for initial connection times and possible retries. It is also
advisable to arrange the time slot during a time of day when the power supply
is most robust. For a solar powered station, this would be the early afternoon.
The periods of power consumption in a day can be divided up as follows:
Period A: the modem is powered off – 0 mA
Period B: the modem powered up in stand-by mode – 300 mA
Period C: the modem is transmitting the data – 2500 mA
Now consider a 35 kB data file size and a datalogger programmed power time
slot of 1/2 hour; the periods above become:
Period A = 24 hours - Period B – Period C
Period B = 30 minutes – Period C
Period C = 3.5 minutes (from TABLE A-1)
We can substitute in the Period B and C values to obtain all Periods:
Period A = 23.5 hours = 0.0 (A hr)/Day
Period B = 26.5 minutes @ 300 mA = 0.1325 (A hr)/Day
Period C = 3.5 minutes @ 2500 mA = 0.1458 (A hr)/Day
The total draw for the data transfer is the sum of the periods, 0.2783 (A hr)/Day,
one day per week.
The (A hr)/Day calculation for each period is as follows:
= Current Draw in mA • (Interval in minutes / 60 min) / 1000
NOTE
NOTE
A-2