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17.3 Polarisation Connector
The polarisation output connector on the rear panel is for Karl Fischer titrations. This titration is a
method for determining minute quantities of water in non-aqueous liquids.
The TPS Double Platinum electrode (part no 122207) has two connectors. The larger BNC
connector fits to any
ONE
of the
Probe 1
,
Probe 2
or
Probe 3
sockets and the smaller 3.5mm
phono plug fits to the
Polarisation
socket.
DO NOT PLUG THE DOUBLE PLATINUM ELECTRODE INTO THE TEMPERATURE
SOCKET.
When performing Karl Fischer titrations, ensure that the selected Channel of the
900-I3
is in
Absolute mV mode.
17.4 Checking the reference junction of a pH electrode
If pH readings are inaccurate or unstable, the reference junction of the electrode may be blocked.
The following test can be performed to determine if the reference junction of a pH electrode is
making adequate contact with the sample solution.
1.
Calibrate the selected Channel of the
900-I3
, as per section 4.3.
2.
Dilute 1 part of pH6.88 buffer with 9 parts of distilled water.
3.
Measure the pH of the diluted buffer. The result should be 7.06 +/-0.02 pH.
4.
If the value obtained is outside of these limits, then clean the reference junction, as per the
instructions supplied with the pH electrode.
5.
Re-calibrate the
900-I3
and repeat the test.
6.
If the value obtained is still outside 7.06 +/-0.02 pH, then the electrode should be replaced.
17.5 Determining if an instrument or pH electrode is faulty
The following test can be performed to help determine if the
900-I3
or the pH electrode is faulty.
1.
Plug the pH electrode into a different Channel, and attempt to calibrate it. If this also fails, then
continue to step 2, below.
2.
Initialise the 900-I3 (see section 14).
3.
Disconnect the pH electrode from the selected Channel.
4.
Connect the centre pin of the
Probe 1
,
Probe 2
or
Probe 3
connector with the outside frame
of the connector, using a short piece of wire or a paper clip etc.
5.
The meter should display approximately pH7.00, depending on the current calibration settings.
6.
If the
900-I3
is operating correctly, the reading should be totally stable with the wire firmly in
place. If not, the meter requires servicing.
7.
Now carefully disconnect the wire from the centre pin only (make sure the other end of the
wire remains connected to the outside frame of the connector).
8.
The reading should steadily drift away from 7.00 (either up or down) at a rate of approximately
1 pH or less every 3 seconds. If the drift rate is faster than this, then input circuitry of the
selected Channel of the
900-I3
is faulty and requires servicing.