MAINTENANCE
Regularly check the module temperature, dark current,
basic current, noise, sensitivity as well as contamination
of quartz disk and reflector.
If the test values deviate significantly from the standard
values specified in the application documents, the error
must be found and eliminated.
How can I measure the dark current?
Shut off combustion air
Close oven
Switch off compensation.
If the dark current is greater than 10
-11
A, check
whether light is entering somewhere on the FPD (see
Replacement of filter).
NOTE:
The recorder deflections corresponding to these detector cur-
rents can be found in Register 5:
Attentuation
.
Check the basic current!
If you use an unconditioned column, you must wait
until a stable basic current has been achieved. This
should be approx. 10
-10
A. If the basic current deviates
by more than 50 % from the value in the application
data, the detector is faulty or the operating parameters
have changed.
IMPORTANT
Components on the Ex-FPD must only be
removed or replaced by a trained Siemens
maintenance engineer or by the user’s
maintenance personnel with subsequent
evaluation by an approved expert according
to §15 Elex V.
Shutting down the FPD
Do not switch off the FPD! First permit the oven to
cool down.
Shut off the detector gases
Allow the detector to cool down
Close the exhaust gas nozzles if the detector is to be
shut down for a longer period.
Ex version: replacing the
interference filter or photomultiplier
The correct filter must be installed for either sulphur or
phosphorus. The filter for sulphur (395 nm) is blue
when viewed in daylight, the filter for phosphorus
(525 nm) is yellow.
IMPORTANT
The photomultiplier in the FPD is very
sensitive to light. Avoid any unnecessary
influence of light on the multiplier, even in
the voltage-free condition. Close the light
entry window when changing the filter or
removing the photomultiplier. Never subject
the light entry window to a bright light
source.
Shut down the FPD
Switch off chromatograph
Remove metal bracket which secures the top part of
the FPD to the housing
Unscrew the heat sink
Loosen the 4 screws on the rear metal plate with
the cable inlets
Loosen two cable clamps
Loosen the two long cylinder head screws with
which the top and bottom parts are connected
Remove the top part from the bottom part. Position
the top part horizontally in the chromatograph
Close the bottom opening of the top part so that no
light can enter
Remove the cover from the top part (four screws)
Loosen the two screws of the socket and pull off
the socket from the tube (11)
Remove tube from top part
Push filter out of its seat from below (using a soft
rod) and shake out of the top part
Refit the new photomultiplier tube or the new filter
in the reverse order. The reflecting side of the filter
must point downwards!
Check that the detector is light-proof: measure the
basic current. The basic current must not become
smaller when you cover the FPD with a dark cloth
Check the measuring sensitivity and selectivity
using a test mixture.
NOTE
The basic current and sensitivity of the new photomulti-
plier may deviate significantly from the values of the old
multiplier. A factor of 2 is normal. The detection limit
(signal/noise ratio) must only differ slightly, however.
FPD - flame photometric detector
4 - 28 EXFPD.CHP Stand September 14, 1999
To Next Page
Loading...
