Troubleshooting - Emerson NGA2000 Reference Manual

NGA2000 Reference
the analyzer basic controls "ZERO" and
"SPAN" buttons will make this happen - it
won't, you have to control them from the
auxiliary module controls as described
above. A future version (post V2.2) of soft-
ware will rectify this automatically. See the
Autocal module manuals for details on how
to set them up.
Network variables: CALTIME, CALTIME-
OUT, ZERO, SPAN, AMFN, CALCHKLIM-
ITS, ZERORNGS, CALRANGES,
CALFAIL, CALFPC
c.

Troubleshooting

Analyzer will not zero...
Verify you have a real zero gas; verify that
the zero gas in the Calibration gas list is set
to whatever the zero gas really is.
See the Result.. menu in the Expert con-
trols section under Zero/span calibration.
The line marked Result of last zero: should
give you a hint as to what happened.
If the analyzer has been changed in some
way, so that its zero reading is quite differ-
ent from what it should be, verify that the
limits checking is turned off in the Calibra-
tion parameters menu. Zero it, then turn the
limits checking back on.
Verify the limits checked for are reasonable
in the Calibration parameters menu.
If all else fails, get into the Factors menu.
Find this under Expert controls and setup,
Expert analyzer controls..., "CAL" softkey,
"FACTORS" softkey, and then select factors
for the range you are using. You can read
the raw signal for the zero gas at the bottom
of this screen. If you edit the Zero factor:
number to be the same as the raw signal,
you will effectively zero the analyzer.
You can see what the stored zero and span
factors were by pressing the softkey marked
"HISTORY". If desired, you can load the
stored or the manufacturing values into the
current values by pressing one or other of
the two RSTR ... softkeys. This will at least
Rosemount Analytical Inc. A Division of Emerson Process Management
Reference Manual
bring the analyzer back to the calibration
factors it used to have. When you are satis-
fied that you do have a good calibration,
you can store the values into the Stored
values variables by pressing the "STORE"
button on the factors screen.
If you have made a large span change, the
zero may be offset excessively. In this case
simply redo the zero and span again.
Analyzer will not span correctly...
See the Analyzer will not zero paragraph
above. In addition, there are a few addi-
tional details.
The values of the span gases must be en-
tered correctly. See the discussion else-
where about errors in span gas bottle
naming. It is easy to replace a span gas
bottle, but to forget to enter the new span
gas values, and therefore to get an inaccu-
rate span. You can guard against this to
some degree by enabling the calibration er-
ror checking, and setting the failure margin
to a low enough value to avoid the worst
mistakes. However this may mean that the
analyzer will not be able to calibrate itself
due to normal drifts, temperature excursions
etc.
If the analyzer has excessive noise, it may
not span to the correct number. In this case
it is necessary to troubleshoot the analyzer
itself.
The fullscale range value must be within
90% to 110% of the linearization range
value, or the linearizer will not be allowed to
apply. In this case, the span may be wrong.
Also the linearizer curve must be monotonic
between -5% and +110% of the fullscale
range.
The analyzer will not span at all...
The span gas value must be within 20% to
110% of the fullscale range value. If it is
outside these limits, the analyzer will simply
not span. Change the fullscale range value,
or the span gas value if that is wrong, so
that you are within these limits.
748384-C
September 2003
Introduction 1-11