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20.5 Determining if an instrument or pH sensor is faulty
The following test can be performed to help determine if the
WP-81T
or the pH
sensor is faulty.
1.
Initialize the
WP-81T
(see section16).
2.
Disconnect the pH electrode.
3.
Connect the centre pin of the
pH
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. If you press the
key, the
WP-81T
will calibrate to around 6.88 pH, depending upon the temperature
readout.
5.
If the
WP-81T
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 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-81T
is faulty and requires servicing.