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Select ESC-Exit and press enter to exit erase mode without erasing any
data.
Select Erase Data Set and press enter to erase the data set that was
displayed before entering erase mode. For example, if data set 12 was
displayed before entering erase mode, and Erase Data Set is selected,
Data Set 12 will be erased from memory and the sets AFTER that
number will move up to keep them sequential. So, if there were 15
records and number 12 is erased then 13 becomes 12, 14 becomes
13, and 15 becomes 14. The instrument will return to data mode after
erasing one data set.
Select Erase All Data Sets and press enter to clear the Pro20/Pro20i
memory and return to data mode.
Exiting Data Mode
While in Data mode, press enter to access the bottom functions. Next,
highlight the ESC-Exit box and press enter to return to the Run screen.
P R I N C I P L E S O F O P E R A T I O N
The polarographic sensor consists of a silver body as the anode and
a circular gold cathode embedded in the end. The galvanic sensor
consists of a zinc anode and silver cathode. The polarographic sensor
requires an applied voltage for operation while the galvanic sensor
electrode potentials are dissimilar enough to reduce oxygen with
applied voltage.
Both sensors have a thin semi-permeable membrane, stretched over
the sensor, which isolates the electrodes from the environment, while
allowing gases to enter. In operation, this end of the sensor is filled
with a solution of electrolyte containing a small amount of surfactant
to improve wetting action.
When a polarizing voltage is applied to the polarographic sensor
electrodes, oxygen that has passed through the membrane reacts at
the cathode causing a current to flow. This same reaction takes place
with the galvanic sensor without the applied voltage.
For both polarographic and galvanic DO sensors, oxygen diffuses
through the membrane at a rate proportional to the oxygen pressure
difference across it. Since oxygen is rapidly consumed at the cathode,
it can be assumed that the oxygen pressure inside the membrane is
