Commissioning the System
111 of 132
Publication S177E V2.0 Issue 12/04
13.4 Diagnostic Information
The master station can provide information via its own display that can help in commissioning and
fault finding.
13.4.1 Loop Configuration
The loop should configure with no loopbacks. If loopbacks are in use (as indicated by the master
station status display), the loop diagnostic screen will indicate which field units have loopbacks
asserted. The line fault will be at or between these units.
A code indicates the reason why loop configuration was last done. This can be useful if the system
repeatedly carries out loop configuration, or fails to configure correctly.
The Port A and Port B LED's may help in indicating what is happening. At start-up or after a "Reset
Loop" command the master station waits until it is sure that all the field units are in loopback. This time
is about 10 seconds at 1200 baud. The Port A LED will come on when there is a complete current
circuit. If it does not come on, there is a break near the Port A end.
The Port A LED then flickers as field units are found and their loopbacks removed. If the loop circuit is
complete, normal scanning will then start as indicated by both LED's flickering together. The master
station status will be reported as ‘Loopbacks Off’.
If the loop continuity is incomplete, the master station switches to Port B after it has found all the field
units connected to Port A. The Port B LED then flickers as field units are found there. Having found all
the field units, the loop has to be left with loopbacks on the last-on-circuit field units only. This involves
waiting for loopbacks to come on again, and then removing all of the loopbacks up to the field unit
Master Station Request
Field Unit Reply
0V
V
Videal
Vmax
Vmax
Adjustable by the potentiometers at the master station
The ideal voltage is 3 volts above V
Videal
(Note that the actual waveform may be rounded due to the charging and discharging of line capacitance.)
Fig 40: Idealised Loop Waveform, monitored at the master station
