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Dissolved Oxygen Sensor
Dissolved Oxygen is measured using an active type membrane covered sensor. The sensor itself consists of silver
and lead electrodes and a 25um PTFE membrane and is filled with a 1.0M potassium hydroxide. A constant flow
of water passes the sensor, maintained by a stirrer located on the bottom section of the probe.
When the silver and lead electrodes are connected through the external circuit, electrons pass from the lead
electrode to the silver electrode. When oxygen is present at the surface of the silver electrode, it reacts with
electrons to produce hydroxyl ions.
At the lead electrode the loss of electrons produces lead ions. The lead's electrons combine with hydroxyl to
precipitate lead hydroxide on the lead electrode.
The rate of transference of electrons via the external circuit from the lead to silver electrode ie that is the
current flowing in the external circuit, is the measure of the rate of cell reaction and thus the rate at which
oxygen reaches the silver electrode. The current flowing in the external circuit is directly related to the oxygen
concentration in the sample being measured by the electrodes.
The Dissolved Oxygen sensor may periodically require a new membrane and electrolyte. A unique knurled nut is
used to hold the sensor membrane in position without overstressing the membrane. This gives long term
stability and allows easy replacement. The sensor can be removed from the probe for servicing. A replacement
probe is ready for use immediately after installation and calibration.
Conductivity Sensor
The conductivity is measured using a 4 electrode bridge. The four electrode system uses automatic
compensation to overcome any build up of contamination on the electrodes. The electrodes are made from fine
platinum and are coated with platinum black to enhance the long term stability and sensitivity of the sensor.
The coating should last for a long period of time if it is not mechanically removed, however, the coating can be
replaced using the optional platiniser or by returning the sensor to YEO-KAL Electronics Pty Ltd.
Turbidity Sensor
The turbidity sensor is located in the hole which runs through the bottom section of the probe and is lined with
a glass tube. Turbidity is measured by the nephelometric method which uses a light source and a detector
measuring the light scattered at 90 degrees to the incident light beam. A pulsed infra-red light source is used.
PH/ORP Sensor
The pH and oxidation reduction potential (ORP) are measured using
separate pH sensor and bare metal platinum electrode for ORP.
They both share an internal reference electrode in the pH sensor.
This sensors has a refillable secondary junction for sensor
maintenance. This sensor with maintenance helps combat
accumulation of internal contamination.