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Instruction Manual
748214-V
June 2009
Rosemount Analytical Inc. A Division of Emerson Process Management Troubleshooting 5-1
Model 951C
SECTION 5
ROUTINE SERVICING
WARNING
ELECTRICAL SHOCK HAZARD
Servicing requires access to live parts
which can cause death or serious injury.
Refer servicing to qualified personnel.
WARNING
INTERNAL ULTRAVIOLET LIGHT HAZARD
Ultraviolet light from the ozone generator
can cause permanent eye damage. Do not
look directly at the ultraviolet source in
ozone generator. Use of ultraviolet
filtering glasses is recommended.
NOTE
The photomultiplier tube must not be exposed to
ambient light. If the photomultiplier tube is ex-
posed to light while the power is on, either
through a loose fitting on the reaction chamber
or any other leak, it will be destroyed. If exposed
to ambient light with the power off, the tube will
be noisy for some period of time. Unless appro-
priate precautions are observed, light can strike
the tube upon removal of fittings from the reac-
tion chamber.
5-1 SYSTEM CHECKS AND ADJUSTMENTS
The following procedures may be used to de-
termine the cause of unsatisfactory instrument
performance, or to make adjustments follow-
ing replacement of components. If a recorder
is available, use it for convenience and maxi-
mum accuracy in the various tests.
a. Display Fullscale Span Adjustment
If a recorder is used, and has been prop-
erly zeroed, it should agree with the dis-
play reading. If not, obtain agreement by
adjustment of R25 on the Signal Board
(see Figure 3-1 (page 3-1) and Figure 3-2
(page 3-2). If agreement cannot be
reached, check the recorder. If the re-
corder is functioning properly, replace the
Signal Conditioning Board.
b. Overall Sensitivity
Principal factors that determine overall
sensitivity of the analyzer are the follow-
ing: (a) sample flow rate to the reaction
chamber, (b) sensitivity of the photomulti-
plier tube (PMT), and (c) PMT high volt-
age. If specified fullscale readings are
unobtainable by adjustment of the SPAN
Control, sensitivity is subnormal. The
cause of reduced sensitivity may be in ei-
ther the flow system (See Section 5-2,
page 5-3) or the electronic circuitry (See
Section 5-6, page 5-10).
If either the High Voltage Board or the
Phototube/Reaction Chamber Assembly
has been replaced, a readjustment of the
high voltage will probably be required to
obtain the correct overall sensitivity. Ad-
just R30 on the Power Supply Board (see
Figure 3-1 page 3-1 and Figure 3-9 page
3-5) clockwise to increase (negative) the
photomultiplier high voltage and sensitiv-
ity, or counterclockwise to decrease
(negative) the voltage and sensitivity.
The adjustment range is about -650 V to
-2100 V for the regulated DC voltage ap-
plied to the photomultiplier tube. Nominal
setting is -1100 volts. However, the volt-
age should be adjusted as required for
overall system sensitivity.