105 Radio/Serial Telemetry Module
User Manual
Page
32
©
January 2004
3.2.5
Indicating a Communications Problem
There are two ways to provide an indication of communications problems.
Fail to transmit alarm.
The first is to map the internal CF status to a local output, to
generate a “fail-to-transmit” alarm. The configured output will activate when a comms fail
occurs - that is, when the module attempts to transmit a message five times without an
acknowledgement. This method provides an indication immediately an attempt to transmit a
message fails. If you want the radio path to be “tested” regularly, then you need to configure
the update times such that transmissions occur regularly (however do not overload the radio
channel).
Notes regarding this method:
1.
Each CF mapping corresponds to only one remote address - you need to make separate
mappings for each remote address. You can map the CF for each remote module to a
separate output, or to the same output.
2.
You need to reset the comms fail output using the “reset output” parameter. Select a reset
time which is greater than the effective update time period. For example, if there are four
inputs mapped from module #1 to module #2, each with a 10 minute update, then you
would expect at least four transmissions in each 10 minute period. At module #1, a
comms fail for #2 is mapped to DO1. If you set the “reset time” for DO1 to 10 minutes,
then there will be at least four transmissions made during the reset period - that is, the
output will only reset when the communications has been successful four times.
3.
This method will not work for radio links with repeaters. If a repeater is used, you will
need to use the second method described below.
Fail to receive alarm.
The second method is to set up a “comms OK” output using the
“Reset Outputs” function. The output is normally on, indicating “comms OK”, and will reset
if the module does not receive a message from the remote module within the configured reset
time.
Consider a link between module #1 and #2, and assume that you want a “comms OK” output
at #1. At #2, map an unused input to an output at #1 such that the output is normally active
(‘on”). If there is no spare inputs at #2, you can use an internal input such as “low voltage
status”. You will need to invert the mappings such that the output is normally on (because
the input is normally off).
At #1, configure a reset time for the output. The reset time should be greater than the update
time for the mapping at #2. If #1 fails to receive update messages from #2, then the output
will reset, indicating a communications failure. Notes regarding this method:
1.
This method will work with repeaters in the link.
2.
The “comms OK” output is fail-safe - if module #1 fails, then the output will reset
indicating a problem.
3.
You should use separate outputs to indicate “comms OK” of different remote modules.
4.
It is recommended that you set the reset time at #1 to more than twice the update time of
the mapping at #2. This means that the comms OK output will only reset if #1 misses two
consecutive updates from #2.