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Using with Campbell Scientific Dataloggers
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will increase significantly – the transmitter using an extra 100-400 mA
depending on where the installation is and the speed of communication.
To achieve even lower power states when using the Loggers IP stack, you
can close the PPP connection at times when you can afford to lose
connectivity. This is done by calling the PPPClose command in your
program to close the link at chosen times and PPPOpen to reopen the link.
Closing the PPP connection will put the modem into a lower power state
(10-15 mA). and also allow the logger to go into its lowest power modem
too (< 1 mA for low activity programs). Once in this state the modem can
still accept incoming GSM dial-up calls providing the modem is set to run in
2G mode either permanently or during this period (see below).
The absolutely lowest power use is achieved by cutting power to the modem
by switching the 12V supply to the modem. When doing this it is important
to deregister the modem from the network before turning off the power.
This is usually done by sending the PPPClose command and sending a
command AT+CFUN=0 to the modem and waiting at least 2 seconds before
turning off the power. Failure to do this may result in subsequent
connections to the network being refused for prolonged periods or the
modem even being barred from the network if this is done frequently. When
powering up the modem again and then using PPPOpen to restart the IP
connection, it is advisable to add delays (of 20s or so) in the program for the
modem to register on the network and the PPP session to start before starting
to send out any data. Please see Appendix A for an example of the CRBasic
code required.
By implication the logger defaults to the PPPOpen state as
soon as a port is activated for PPP. This is not dependent on a
program running. To stop a PPP connection being made when
a program is recompiled, include a PPPClose instruction after
the BEGIN instruction. Do this with consideration because if
you load a program that incorrectly calls PPPClose you could
block further communications.
If using the Modem IP stack, there are less options for shutting down the IP
link. It is not normally practical to reconfigure the modem by sending it
commands from the logger, especially with older loggers. The data logger
will sometimes go into a lower power state if there are periods of no
communications but the modem will remain powered. Normally the only
option beyond this is to switch the power to the modem. If this is done,
avoid doing this too frequently as it is not possible to cleanly log off from
the network, which can lead to delays in registering the modem when power
is restored.
In either mode of operation you can optimise power use by writing code to
only turn the modem on for limited periods and use the “call-back” function
to Loggernet (see above) where the logger calls back and using the
Sendvariables command which in turn triggers Loggernet to do a normal
data collection from the logger. The power can be controlled to enable the
modem only during the call-back
4.5 Sending configuration commands to the modem
It is often advisable to reset the modem at regular intervals or send other
configuration commands to the modem, for instance to enable very low
power states between calls. When using the loggers IP Stack, this can be
done within the data logger program by opening the serial port to which the
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