User guide

A-1

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 metrological 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 124Kb.

If the station’s data were downloaded monthly, the time (T) for the data transfer

could be calculated as shown below:

(Download)

= File size (Kb) / Transfer Rate (10 Kb/min)

With a file size of 124 Kb and a transfer rate of 10 Kbytes per minute, the

download time is approximately 13 minutes.

If the data were downloaded daily, the file would be much smaller, approximately

5KB. 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 4 below shows the transfer time depending on whether data is collected

daily, weekly or monthly.

Collection Interval

File size (Kbytes)

Transfer time

Monthly

124

13 minutes

Weekly

3.5 minutes

Daily

30 seconds

Table 4. Data Transfer Time Estimates

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