YSI 85 - Manual (Page 34)

Discussion of Measurement Errors Section 11
YSI, Incorporated Model 85 30
solution. Errors will be most serious when low conductivity solutions are contaminated by carry-
over from high conductivity solutions, and can then be of an order of magnitude or more.
Follow the cleaning instructions carefully before attempting low conductivity measurements with a
cell of unknown history or one that has been previously used in higher value solutions.
An entirely different form of contamination sometimes occurs due to a buildup of foreign material
directly on cell electrodes. While rare, such deposits have, on occasion, markedly reduced the
effectiveness of the electrodes. The result is an erroneously low conductance reading.
Electrical-Noise Errors
Electrical noise can be a problem in any measurement range, but will contribute the most error and
be the most difficult to eliminate when operating in the lowest ranges. The noise may be either line-
conducted or radiated or both, and may require, grounding, shielding, or both.
Galvanic and Miscellaneous Effects
In addition to the error sources described above, there is another class of contributors that can be
ignored for all but the most meticulous of laboratory measurements. These errors are always small
and are generally completely masked by the error budget for cell-constant calibration, instrument
accuracy, etc. Examples range from parasitic reactance associated with the solution container and its
proximity to external objects to the minor galvanic effects resulting from oxide formation or
deposition on electrodes. Only trial and error in the actual measurement environment can be
suggested as an approach to reduce such errors. If the reading does not change as the setup is
adjusted, errors due to such factors can be considered too small to see.