Campbell Scientific 9522B Iridium Satellite Modem and COM9522B Interface Modem - Manual (Page 31)

Appendix A. Sample Data Transfer
Calculations
The calculations below are based upon maximum theoretical
throughputs. Real world transmission times for the Iridium
Satellite Network have proven to be as much as twice as slow.
When transmitting the data back from the station, the power consumption of
the modem must be taken into account in order to avoid excessive discharge of
the battery power supply. To get an idea of what the transmission time and
associated power drain might be for a typical meteorological station, consider
the following example:
A station measures wind speed and direction, precipitation, temperature and
relative humidity, solar radiation, and barometric pressure. The datalogger is a
CR1000. The monthly data file contains 2 data tables; a small maintenance
table and a 30 parameter meteorological data table. The size of a monthly
ASCII data file is 124 kB.
If the station’s data were downloaded monthly, the time (T) for the data
transfer could be calculated as shown below:
T
(Download)
= File size (kB) / Transfer Rate (10 kB/min)
With a file size of 124 kB and a transfer rate of 10 kB per minute, the
download time is approximately 13 minutes.
If the data were downloaded daily, the file would be much smaller,
approximately 5 kB. A daily data transfer time would be approximately 30
seconds. Please note that a 15 second connection time should be added to the
above times to account for the initial connection time.
TABLE A-1 below shows the transfer time depending on whether data is
collected daily, weekly, or monthly.
TABLE A-1. Data Transfer Time Estimates
Collection Interval File size (kB) Transfer time
Monthly
124 13 minutes
Weekly 35 3.5 minutes
Daily 5 30 seconds
The CR10X datalogger generates data arrays which are very similar in size to
the table-based dataloggers. For example, the station mentioned above
generates a 124 kB meteorological data table and a 2 kB maintenance table
each month. If a CR10X is employed to measure the same parameters, the data
arrays would be the same size.
NOTE
A-1