Chapter Three
Operation
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approx 4m, requiring each antenna to be elevated at least 5m to achieve “line-of-sight” even
if the path is flat.
A radio path may act reliably in good weather, but poorly in bad weather - this is called a
“marginal” radio path. If the radio path is more than 20% of the maximum reliable distance
(see Specification section for these distances), we recommend that you test the radio path
before installation. Each 105U module has a radio path testing feature - refer to section 6.2
of this manual.
There are several ways of improving a marginal path :-
•
Relocate the antenna to a better position. If there is an obvious obstruction causing the
problem, then locating the antenna to the side or higher will improve the path. If the radio
path has a large distance, then increasing the height of the antenna will improve the path.
•
Use an antenna with a higher gain. Before you do this, make sure that the radiated power
from the new antenna is still within the regulations of your country. If you have a long
length of coaxial cable, you can use a higher gain antenna to cancel the losses in the
coaxial cable.
•
If it is not practical to improve a marginal path, then the last method is to use another
module as a repeater. A repeater does not have to be between the two modules (although
often it is). If possible, use an existing module in the system which has good radio path to
both modules. The repeater module can be to the side of the two modules, or even behind
one of the modules, if the repeater module is installed at a high location (for example, a
tower or mast). Repeater modules can have their own I/O and act as a “normal” 105U
module in the system.
3.2.4
Design for Failures
All well designed systems consider system failure. I/O systems operating on a wire link will
fail eventually, and a radio system is the same. Failures could be short-term (interference on
the radio channel or power supply failure) or long-term (equipment failure).
The 105 modules provide the following features for system failure :-
•
Outputs can reset if they do not receive a message within a configured time. If an output
should receive an update or change message every 10 minutes, and it has not received a
message within this time, then some form of failure is likely. If the output is controlling
some machinery, then it is good design to switch off this equipment until communications
has been re-established.
The 105 modules provide a “drop outputs on comms fail” time. This is a configurable
time value for 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 105 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.
