Ensure there is some pH probe keeper in the protector cap before replacing on the ph sensor.
Turbidity Sensor Maintenance
The turbidity sensor requires little maintenance except ensuring that the turbidity screen (a black
acetyl optical screen) be kept free of accumulated grit and mud and every so often it should be
removed and cleaned. The glass tube should also be cleaned with a damp paper towel or a small
bottle brush. Recalibration of this sensor after cleaning is required.
Removing the screen is achieved by unscrewing the two retaining screws at the bottom of the
probe, situated on the flange. Pull the black screen out and wash it and also clean the glass tube.
Reinsert the screen and do up the two retaining screws – an orientation mark exists which should
face the centre of the probe.
Conductivity Sensor Maintenance
To maintain the performance and accuracy of the conductivity / salinity sensor, the electrodes need
to be periodically cleaned and if the platinum black coating is damaged, the electrodes will need to
be re‐platinised.
Inspect the sensor on a regular basis. If there is any evidence of a build up of contamination on the
electrodes, then the sensor should be removed and cleaned using the platiniser unit as described
below. If the platinum black coating is damaged, the electrodes should be cleaned and then re‐
platinised. To perform these operations, proceed as follows:
1.
To remove the sensor, lift the sensor guard and rotate the bottom section of the probe to
expose the sensors. Ensure that the probe and sensors are completely dry. Use a cotton
bud to dry the area between the sensors. Pull the conductivity sensor down out of the
probe by hand. Do not twist the sensor. Ensure that the vacant sensor socket is kept
completely dry.
2.
To clean the electrodes, plug the sensor into the platiniser unit. Connect the unit to a 6V
power supply (such as a lantern battery). Fill the platiniser with 0.1M HCl and switch on the
platiniser for 5 minutes. Switch off the platiniser and rinse with distilled water. Now inspect
the electrodes. If the platinum black coating is intact, replace the sensor in the probe
assembly as described in step 5 below. If the electrodes need to be re‐platinised, proceed
as follows.
3.
To strip the old platinum black coating from the electrodes, plug the sensor into the
platiniser unit fill with 5M HCl. Connect the unit to a 6V power supply and switch the unit
on. The old platinum black will be stripped off the electrodes. Once completed, switch the
platiniser off and rinse with distilled water.
4.
To replace the electrode coating, plug the sensor into the platiniser unit and connect to a
6V power supply. To make the platinising solution, mix 3g of chloroplatinic acid with 0.3g of
lead acetate and top up to 100ml with distilled water. Fill the platiniser with platinising
solution and switch the unit on for 10 minutes. The electrodes will be plated with a sooty
black coating. When complete, rinse the unit and electrodes with distilled water then fill
the unit with 0.1M HCl and switch on for 2 minutes to remove any occluded platinum black
solution remaining on the electrodes. Rinse the sensor and platiniser with distilled water
and install the sensor in the probe assembly.
5.
Before installing the conductivity sensor into the probe assembly, make sure that both the
sensor and probe assembly are dry. Apply a smear of vacuum grease to the sensor body to