User manual

905U Wireless I/O Module User Manual
105S Serial I/O Module
Page 32 © October 2001
each output. If a message has not been received for this output within this time, then the output will
reset (off, in-active, “0”). We suggest that this reset time be a little more than twice the update time
of the input. It is possible to miss one update message because of short-term radio interference,
however if two successive update messages are missed, then long term failure is likely and the
output should be reset. For example, if the input update time is 3 minutes, set the output reset time
to 7 minutes.
• A module can provide an output which activates on communication failure to another module. This
can be used to provide an external alarm that there is a system fault.
3.2.5 Indicating a Communications Problem
There are two ways to provide an indication of communications problems. The first is to map the
internal CF status to a local output. The output will then activate when a comms fail occurs. 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.
The second method is to set up a “comms OK” output using the “Reset Outputs” function. 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