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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 915U-2 module has a radio path-testing feature -
refer to Section 5.2 "Connectivity" 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" 915U-2 module in the
system.
3.3.3 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 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 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.
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915U-2 Wireless I/O
915U-2 Wireless I/O
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