Using with Campbell Scientific Dataloggers
More commonly if you have a dynamic IP SIM you will not be able to call out to
the logger as it is on a private network behind a router/firewall. Instead you have
to get the datalogger or modem to open a connection back to the Loggernet PC
which itself must have a public IP address (see firewall issues below) and have
Loggernet hold the connection open.
There are two ways of doing this.
1)
Using the Datalogger TCP/IP stack you can configure the logger to
automatically establish a socket connection to a remote system, e.g. your
Loggernet server. It will do this as soon as it is powered up and a PPP
connection is established. It will try to open the socket once per second, until
successful. This is done by entering the IP address and socket in the Net
Services tab, as a Pakbus/TCP Server settings (the Mobile Data Assistant will
set this for you if you choose the Logger Call-back option). This method is
easy to setup and does not rely on the datalogger program.
If you are using the Modem IP/Stack the Mobile Data Assistant package
enables a similar function in the modem, which tries to keep open a
permanent connection to the socket on a server (normally running Loggernet).
2)
Alternatively you can call the TCPOpen/TCPClose command in your
program at regular intervals (the speed determines how quickly the logger
will re-establish a broken link). In the TCPOpen command you need to give
the public address of the Loggernet server and the port you are going to
connect on. This method is only normally used where the logger needs to
conserve power so the modem is not on all of the time or more than four
connections to different servers are required.
When using the Modem IP/Stack for a program controlled call-back the modem
will only make the IP connection when it receives data from the attached logger to
transmit. Normally you would trigger the connection by using the standard call-
back commands in the logger program, which would trigger data exchange with
Loggernet on a direct connection, e.g. P97 for older loggers, or SendGetVariables
for newer Pakbus loggers.
For either method the port (socket) number must match the call-back port number
entered in the setup screen of Loggernet (see below). You should also enable call-
back for the datalogger on the datalogger hardware tab.
The method of managing Loggers which call back over IP varies with the
Loggernet version. Loggernet 4.1 or later is recommended. A description of how
to setup Loggernet for call-back is given in Section 9.2 below.
5.4 GPRS - Minimising call costs and power use
If the modem is used in an “always-on” configuration, to allow instant access, the
modem will stay in a higher power state for most of the time. It is critical to take
this into consideration when considering suitable power supplies and battery sizes.
The always on-configuration also requires some network traffic to flow to keep
the connection open, which will use up some of your GPRS data allowance.
The average power consumption of the COM110 when there is an open
PPP/GPRS connection will typically be 30 mA. With only low level traffic
flowing through the connection the datalogger itself will often be able to drop into
a lower power state, i.e. not consume extra current. However, during
communications activity both the datalogger and modem power use will increase
significantly – the transmitter using an extra 100-400 mA depending on the
installation and speed of communication.
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