WattMaster WM-WCC3-TGD-01B - Manual (Page 765)

WCC III Technical Guide 20-7
20. GLOBAL BRIDGE BOARD INSTALLATION
Step 3:
SAT II controller Manchester boards’ impedance
mismatching problem:
a. When installing a new SAT II controller to your system,
the new SAT II controller appears to not work and/or other
previous working SAT II controllers now stop communicating.
This is a classic Manchester board impedance mismatching
problem. It is a diffi cult problem to fi x. The fi x involves
updating all of your SAT II controllers’ Manchester boards to
the current impedance.
b. Newer SAT II controllers Manchester boards have a
different RT to C resistance impedance than the much older
Manchester boards (more than 15 years old). The “New” RT
to C resistance should read about 120 ohms (+/-15 ohms).
c. Older Manchester boards have RT to C resistance
impedance’s of 18 (+/- 5) ohms or some even have
impedances of over 200 ohms. To guarantee the proper
operation of the WCC II communications loop, all SAT II
controllers Manchester boards should have the same RT to C
resistances. It has been WattMaster’s experience that when
the SAT II controllers’ Manchester boards’ impedances match,
the WCC II communications loop will work. Also, it is
recommended that the whole SAT II controller as a complete
assembly will need to be rebuilt and have all of the latest
upgrades preformed.
Step 4:
Have you run the LOOPTEST diagnostics on the WCC
II computer?
a. The Looptest program must be run with 1000 passes
per SAT II controller in order to determine if a WCC II
communication problem exists with a particular SAT II
controller.
b. Make note of any failures of all of your SAT II controllers
on the loop as this will be useful in determining if a WCC II
communications problem exists.
c. If a SAT is failing a lot of passes (20 %), then disconnect
it from the communications loop. It could be causing an
intermittent communications problem with other SAT II
controllers that are on the WCC II communications loop.
d. It would be also helpful if you know how the
communications loop was ran - if it was split into multiple
loops converging into one at some point - because one of these
WCC II communications loops may be cut or disconnected,
and this may be the source of your problem.
NOTE: Before testing the Z-80 board for loop test diagnostics,
the clock chip on the WCC II front-end computer’s Z-80
board must be initialized. This is best done by setting the time
and date from within the WCC II program via the System
Parameters Screen. If the time and date are not initialized, this
could cause 3 or 4 failed passes per 1000 passes.
Troubleshooting Communication Loops