105 Radio/Serial Telemetry Module
User Manual
Page
74
©
January 2004
update time at the remote module (both
have been left at their default value of
1 minute).
•
Reset times have been selected for the
analogue outputs (21 minutes) but not
the digital outputs. In the event of a
system failure, the digital outputs will
stay at their last correct status, but the
analogue outputs will reset to 0 mA.
System Failure Alarm
After the system had been running for
some time, the operators wanted a
"system failure" output at the control
station, to warn the operators that
there was a fault with the system.
The following configuration was
added:
At #2 (tank station), Inverse DI4
→
DO4 at #96 via 1 ; DI4 Update time =
1 minute
At #96 (control station), DO4 Comms
fail reset time = 3.5 min
At the control station, DO4 was a
"system OK" signal. It was normally
active - if the signal reset, then this
represented a system failure. At the
tank station, there is no signal wired
to DI4. By mapping Inv DI4 to DO4
at the control station, a message is transmitted every minute to this output to activate it. The
message is transmitted via the radio link to #1, and then by the serial link to #96. If anything
happened to either module #2 or module #1, or the radio link, or the serial link, then the
update messages for DO4 will not be received at the control station module. After 3.5
Minutes, DO4 will reset indicating a problem.
The time of 3.5 minutes was selected as this means that 3 successive update messages have to
be missed before a system alarm occurs. Also note, that if module #96 fails, DO4 will reset
and give an alarm signal.
