Metrohm 781 pH/Ion Meter - Manual (Page 137)

8 Troubleshooting – Messages – Maintenance
780/781 pH/Ion Meter, Manual
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With a 801 Magnetic Stirrer the test is fully automated. You just have to
change the buffers. Set the stirring rate at
PARAMETER pH/measuring parameters/stirrer:
stirring rate
The stirring rate should be set so that the stirring action is powerful but
without the formation of air bubbles (avoidance of absorbing CO
2
).
Metrohm stirrers which are connected to the pH/Ion Meter are switched
on and off automatically when the measuring parameter stirrer (see
above) is set to 'ON' . If an unconnected stirrer is used then you will
have to switch it on and off manually during the test. A request will be
made at the appropriate places during the test. The measuring parame-
ter stirrer must thereby be set to 'OFF' .
Printer
If you want to print out either a full or short test report then a printer
must be connected (see Section 2.3) and its configuration set properly
(see Section 5.6 and 5.7).
Parameter settings
Before the start of the electrode test it may be necessary to adapt the
electrode test parameters. These parameters are described in Sec-
tion 6.2.7.
Temperature
Please ensure that the whole electrode test is carried out at a constant
temperature. As the temperature has a great influence on the response
time you should work at room temperature if possible. The preset toler-
ances are set for 25 °C.
In the following section the exact electrode test procedure is described.
It is assumed that a temperature sensor is connected: if not, you must
determine the measuring temperature manually and enter it at the start
of the electrode test when the request for it appears on the display.
8.6.2 Procedure
The whole pH electrode test is dialog guided; this means that you will
be requested to carry out any activity which is required. The sequence
is as follows: the pH electrode is first immersed in the pH 9 buffer and
its potential is measuring for three minutes under stirring followed by
one minute without stirring. The same measurements are then repeated
at pH 4 and pH 7. If no controllable stirrer is connected you will be re-
quested to switch the stirrer on and off at the required times.
In order to obtain realistic response times the electrode should be im-
mersed in each buffer at about the same time as the measurement is
started and it should be positioned directly above the stirrer which has
already been switched on.
The pH/Ion Meter in the pH mode should be in the normal working
condition (measured value display). Otherwise switch to this mode with
.