Instruction Manual
760000-C
November 2002
4-4 Maintenance and Service
Rosemount Analytical Inc. A Division of Emerson Process Management
Model NGA2000 CLD
c. Photodiode
Removal
Remove the Detector Assembly as described
above. Invert the housing to access the
mounting bracket. Remove the (3) screws
and shoulder washers from the bracket. Re-
move the bracket, insulating disk and bottom
plate as a unit to minimize the spread of the
heatsink compound.
Remove the (2) screws holding the lower
section of the Detector Housing, then slide
the section along the cable and remove.
Remove the (2) screws holding the socket,
thermistor and photodiode in place, being
careful not to lose the washers that are used
as shims.
Grasp the socket and photodiode base while
slowly rotating to separate the photodiode
from the housing. Some friction will be felt as
an O-ring is used around the photodiode as a
seal.
d. Photodiode
Installation
To replace the photodiode, carefully remove
the diode from the green socket, and replace
with a new one. Before mounting the new di-
ode, the top cap of the enclosure should
be temporarily removed and the (2)
screws holding the Reaction Chamber
loosened about two turns. This allows air
which is trapped between the O-ring seals
to escape when the diode is inserted. It
also maintains the position of the O-ring
and window in the upper compartment.
The new photodiode should be slowly in-
serted into the housing while gradually ro-
tating the body. This allows the O-ring to
properly seat. Continue replacing screws,
washers, thermistors, etc., with the thicker
shim (washer) on the opposite side of the
socket from the thermistor.
Replace the lower section of the housing,
then the bottom cover, insulator and
bracket with the shoulder washers and
screws.
Re-tighten the screws in the Reaction
Chamber (upper section). Replace the top
cap and its screws.
To reinstall in the Analyzer Module, re-
verse the procedure for removal as indi-
cated above.
