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7835
Hydrazine Monitor
9.4.3 Cleaning The Platinum Anode and Sensor Ceramic
1. Switch off sample flow to the monitor.
2. Loosen the rubber bung on the top of the sensor and
carefully withdraw the platinum anode from the centre of
the ceramic tube.
3. Insert the brush, supplied in the sensor kit, down the bore
of the ceramic tube (ensuring it still contains some sample)
rotate gently and withdraw.
Warning. Avoid any spillage of acid and take care not
to allow any acid to touch the rubber bung.
4. Clean the platinum anode by immersing it in a test tube
containing 50 % nitric acid for a few minutes.
5. Rinse the electrode in high purity water and return it to the
sensor.
Blue
Temperature
Sensor
Sensor Outer
Jacket Filled
with Gel/Silver
Oxide Mixture
O-ring
Sample Inlet
Nipple
Fig. 9.2 Hydrazine Sensor
9.4.4 Sensor Check
Before checking the sensor, ensure that the fault condition is not
due to incorrect sample and calibration flow rates caused by an
air bubble in the sensor or flow line. To remove air, lift the
platinum electrode slightly by the rubber bung and allow some
liquid to escape, carrying any bubbles with it. Alternatively,
connect a syringe to the sensor outlet and apply slight suction.
IM/7835–EN Rev. P
9.4.5 Refurbishing The Sensor
A good indication of whether the sensor needs refurbishing is
the state of the gel in the outer jacket. If the gel appears to have
dried out, separated or become liquid, the sensor requires
refurbishing.
Sensor disassembly
Referring to Fig. 9.2, page 25:
Red
Rubber Bung
Plug and Platinum
Wire Anode
Assembly
Sample Outlet
O-ring
Vent Hole
Silver Wire
Cathode
Ceramic Tube
Filling Hole
1. Close the sample isolator valve and allow the constant
head unit to empty.
2. Turn the sensor plugs, located on the side of the liquid
handling panel, half turn anticlockwise and disconnect
them by pulling them from the sockets.
3. Carefully pull the hydrazine sensor out of its mounting clips
on the sub-panel.
Warning. The gel in the hydrazine sensor contains
silver oxide and sodium hydroxide. It is caustic and
stains skin and clothing.
4. Holding the sensor over the drain tundish, pull off the
sample inlet tube and let the tube and sensor drain. Leave
the end of the inlet tube dipping into the tundish.
5. Carefully dismantle the sensor as detailed below and wash
the components thoroughly to remove all traces of gel.
6. Clean the ceramic and the platinum anode as shown in
Section 9.4.3, page 25.
Warning. Avoid any spillage of acid, and take care to
keep all electrical connectors free of acid.
7. If still in place, remove the outer jacket of the sensor.
8. If the silver cathode is tarnished or blackened, dip a cotton
wool bud in 50 % nitric acid and clean the wire to restore it
to its original matt silver color. Rinse thoroughly with high
purity water.
9. Rinse the cotton wool bud and safely dispose of it.
10. Loosen the rubber bung on the top of the sensor and
carefully withdraw the platinum anode from the centre of
the ceramic tube.
Warning. Clean up any spillage of the caustic
solution.
11. Soak the ceramic tube for 1 hour in 2 % sodium hydroxide
solution, rinse with high purity water and reassemble the
sensor.
9 Maintenance
25
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