YSI 3200 - Manual (Page 55)

Principles of Operation Section 8
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 using the lowest conductance settings. The noise may
be either line-conducted or radiated or both, and may require revised lead dress, grounding,
shielding, or all three. Often, all that is necessary is to make sure that parallel leads are of equal
length and twisted together.
CONTACT RESISTANCE
YSI 3200 series cells utilize a 4-wire connection virtually eliminating errors due to contact
resistance.
When using the YSI 3232 cell adapter to connect a 2-wire cell (such as the YSI 3400 series cells),
contact resistance can be a source of error when measuring high conductivity. Lugs should be
clean and free of mechanical distortion. They should fit squarely on terminal posts that are
properly tightened. Leads should also be inspected to verify that no physical damage has occurred
that might degrade electrical contact.
CABLE SERIES RESISTANCE AND SHUNT CAPACITANCE
YSI 3200 series cells utilize a 4-wire connection virtually eliminating errors due to cable
resistance.
The short cables provided as a part of regular cell assemblies will introduce negligible error in
most measurements. However, if longer cables are required or if extraordinary accuracy is
necessary, special precautions may be prudent.
When using the YSI 3232 cell adapter and a 2-wire cell (such as the YSI 3400 series cells) with
solutions having very high conductivity values, a high cable resistance will become a major
source of error unless accounted for. When working with solutions having very low conductivity
values and long cables with large capacitance, such as might be used with a flow-through cells at
remote locations, the large cable capacitance will become a major source of error.
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.
YSI Incorporated Model 3200 51