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8 SIMPLE FAULT FINDING
8.1 Maintenance
No routine maintenance is required for this instrument other
than periodic calibration – see Section 6.2.2. However, if
following a calibration the sensor output shows two flashing
bars, the sensor capsule has therefore become exhausted
and needs replacing immediately.
If the output shows three bars, replace the sensor capsule in
the near future.
A dirty membrane may also be the cause of the low sensor
output. To clean the sensor procede with the following.
8.1.1 Cleaning/Changing the Sensor
Caution.
• Only install the oxygen sensor immediately prior to
use, otherwise leave it stored in its protective
container.
• Take special care to line up the two pins in the oxygen
sensor with their respective sockets before making the
connection and tightening.
• Take care not to damage the delicate membrane on
the end of the oxygen sensor.
• Ensure that the mating surfaces (carrying the
electrical connection) of the oxygen sensor and
connector body are clean and completely dry.
1) Isolate and drain the flowcell.
2) Unscrew the clamping screw and remove the sensor
assembly from the flowcell.
3) Inspect the sensor. If the membrane is clean, replace the
sensor – proceed to 4) below.
If deposits are visible on the membrane, remove them by
gently wiping the membrane with a moist paper tissue; for
oily or greasy deposits, the tissue may be moistened with a
mild detergent or, if necessary, with iso-propyl alcohol
(propan - 2 - ol). After cleaning, dry the interior of the
flowcell with a paper tissue or soft cloth, ensure that the
O-ring is correctly positioned against the shoulder near the
end of the cavity – proceed to 11) below to test the sensor.
4) Unscrew the connector nut; remove the sensor capsule
and discard both capsule and sealing washer.
5) Take out the O-ring from the flowcell; dry the interior of the
flowcell with a tissue or soft cloth and insert the new O-ring
supplied with the replacement capsule. Ensure that the
O-ring is correctly located on the shoulder near the end of
the cavity.
6) Remove the top from the container of the new sensor.
7) Unscrew the protective cap from the rear of the sensor
8) Place a new sealing washer (supplied) as shown in Fig. 4.1
and locate the connector body on the sensor.
9) Slip the connector nut over the connector body and screw
onto the sensor firmly.
10)Slide the thrust washer over the connector body.
24
11) Insert the complete assembly into the flowcell.
12)Use the clamping screw to secure the assembly. Screw in
firmly using finger pressure only.
Caution. Do not overtighten the clamping screw.
13)Reinstate sample flow through the flowcell.
14)Carry out a calibration – see Section 6.2.2.
8.2 Error Messages
If erroneous or unexpected results are obtained the fault may
be indicated by an error message – see Table 8.1.
Table 8.1 Error Messages
E
r r
r o
M
e
s
s
a
g
e
F
A
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L
T
Y
P
T
1
0
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N
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M
E
M
O
R
Y
m
e
E
R
R
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c
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*
This message applies the last D.O. calibration carried out
prior to power-down and is not an indication of incorrect
electrical calibration.
** To rectify the fault, switch off, wait 10 seconds and switch
on again. If the fault persists contact the Company.
8.3 Low Sensor Output or no Response to D.O. Changes
Replace the sensor (see Section 8.1.1) as an initial check. It is
also important that all program parameters have been set
correctly and have not been altered inadvertently – see
Section 7.
If the fault persists:
a) Carry out an electrical calibration as detailed in Section 7
and check that the instrument responds correctly to the
current input.
Failure to respond to the input usually indicates a fault with
the transmitter, which must be returned to the Company for
repair.
b) If the response in a) is correct, select the Operating Page
and set the current source to a value which gives an on-
scale D.O. reading on the transmitter. Make a note of the
current source setting and the D.O. reading. Reconnect
P
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