YSI 85 - Manual (Page 30)

Principles of Operation Section 10
YSI, Incorporated Model 85 26
Specific Conductance (25°C) = Conductivity
1 + TC * (T - 25)
As noted above, unless the solution being measured consists of pure KCl in water, this temperature
compensated value will be somewhat inaccurate, but the equation with a value of TC = 0.0191 will
provide a close approximation for solutions of many common salts such as NaCl and NH
4
Cl and for
seawater.
Salinity is determined automatically from the Model 85 conductivity readings according to
algorithms found in Standard Methods for the Examination of Water and Wastewater (ed. 1989).
The use of the Practical Salinity Scale 1978 results in values which are unitless, since the
measurements are carried out in reference to the conductivity of standard seawater at 15 C.
However, the unitless salinity values are very close to those determined by the previously-used
method where the mass of dissolved salts in a given mass of water (parts per thousand) was reported.
Hence, the designation "ppt" is reported by the instrument to provide a more conventional output.
For further information on conductivity and the above standard information, refer to the ASTM
document, Standard Methods of Test for Electrical Conductivity of Water and Industrial
Wastewater, ASTM Designation D1125-82, and OIML Recommendation Number 56. ASTM
symbols for conductivity, cell constant, and path length differ from those preferred in the general
literature and also from those used in this manual.