Appendix B Terminal Layouts
man_905-105_2.16 Page 81
• PO 3 has been configured as a PO. Its pulse
output update time is the same as the PI update
time at the remote module (both have been left
at their default value of 1 minute).
• Reset times have been selected for the analog
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 analog 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.
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