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20.5 Determining if a pH meter or a sensor is faulty
The following test can be performed to help determine if the
WP-90
or the pH
sensor is faulty.
1.
Initialise the
WP-90
(see section 17).
2.
Disconnect the pH sensor.
3.
Connect the centre pin of the
SENSOR
connector with the outside frame of
the connector, using a short piece of wire or a paper clip etc.
4.
The meter should read approximately 7.00. The
WP-90
will now pH
calibrate to around 6.88 or 7.00 pH, depending upon the temperature readout
and the primary buffer selection (section 16).
5.
If the
WP-90
is operating correctly, the reading should be totally stable with
the wire firmly in place. If not, the meter requires servicing.
6.
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).
7.
The reading should steadily drift away from 6.88 or 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
WP-90
is faulty and requires
servicing.