YSI 3100 - Manual (Page 31)

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7.4 Temperature
The Model 3100 system utilizes a thermistor of sintered metallic oxide which changes
predictably in resistance with temperature variation. The algorithm for conversion of resistance
to temperature is built-in to the Model 3100 software, and accurate temperature readings in
degrees Celsius or Fahrenheit are provided automatically. No calibration or maintenance of the
temperature sensor is required.
7.5 Sources of Errors
Cell Contamination
This error is usually due to contamination of the cell by some previous solution. Normally this is
in the form of an organic film which reduces the solution-electrode interface conductance.
Follow the cleaning instructions carefully.
An entirely different form of contamination sometimes occurs when cells are stored for long
periods of time wet; alga and other life forms grow on the electrodes. While rare, such deposits
have, on occasion, markedly reduced the effectiveness of the cell by reducing the solution-
electrode interface conductance.
Cell Platinizing
Errors can be introduced by cells that have begun to lose their electrode coating of platinum
black when measuring solutions having high conductivity values. The effect of poor platinization
is a loss of linearity and a noticeably large change in conductance from range to range on the
instrument.
When you suspect a problem with the cell platinization, follow the instructions for electrode
inspection and replatinization carefully before attempting any critical measurements.
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.