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Siemens TC35T GSM Digital Transceiver
12
Campbell Scientific communications software includes other time-outs which are
used to check for hung communications links. These are set to be quite short for
land-based modems, as the response to any command sent from the PC should be
almost instantaneous. A link to a remote TC35T normally passes through several
nodes of a digital data network, all of which can add delays. Usually these delays
are less than one second and so have no effect on the communications process.
However, on a long distance call or busy network, the built in time-out delay for
the PC software may need to be extended.
Using PC208W, a station-specific delay can be added by increasing the time in the
‘Extra response time’ box shown on the datalogger hardware set-up screen. This
delay is entered in milliseconds. PC208W (version 3 or later) has a default extra-
response delay of 2000 milliseconds, which is adequate for use with the TC35T in
most cases. (Older versions of the support software have a default setting of zero
milliseconds and this value will need to be increased, but it is strongly
recommended that you use PC208W version 3 or later.) On busy networks, or with
poor communication links, a value of 3000 or even 4000 may be required, to allow
the error correction process to function.
Where a TC35T is used as the base station modem, it is advisable to increase these
delays even more by perhaps another 1000-2000 milliseconds, if communications
are proving to be unreliable.
Entering too large a delay can slow down the entire communications
process, and so an optimal value should be determined by trial and
error.
If using Loggernet 2.0 you should be aware that extra response
delays are entered in seconds rather than milliseconds.
6.4 Ending a Call
If the SC932 or SC932C interface is being used, the communications session is
ended when either:
a)
the datalogger is told to finish the communications session by the PC
OR
b)
one of the datalogger time-outs causes the call to finish
One of the two conditions described above will cause the datalogger to lower the
DTR line and force the modem off-line. Some GSM networks are unable to signal
this change of state back to the calling modem, in which case the calling modem
will often stay on-line and sometimes receive what appears to be random data from
the network.
Usually the PC software will detect this as an error and force the calling modem
off-line. Current versions of PC208W will ensure the modem is forced off-line as
quickly as possible in this event; older software may remain on-line for an extra
one or two minutes and so could incur extra phone charges.
NOTE