with the top and bottom units functioning only as‘ dummies’.
Measurement begins with Watson wrapping the metal cap of the disc with tape to prevent its deposited contamination from impacting the reading on the actual insulation surface. The glass is then washed thoroughly in a tub of de-mineralized water of constant one-liter volume before a meter reads conductivity of the resulting solution. Temperature of the water is also recorded to correct conductance values to a standard 20 ° C.
Knowing the area of the glass disc( in this case 583.9 cm 2 at the top and 704 cm 2 at the bottom), associated ESDD values can be calculated for each. Readings are then averaged out and charted over time for every disc sampled from the string, along with information on rainfall to allow a more complete picture of the real pollution scenario.
Watson reports that ESDD readings for each disc typically vary by location in the string, with discs in certain positions more likely to accumulate pollution due to aerodynamic effects. Data is then sent to Eskom’ s planning department
Photos: INMR ©
I Conductivity measurements made after fixed volume of de-mineralized water added to contents of DDG containers.
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