Thermo Electron CorporationIX-2 Orion Star Series Meter
Conductivity Technique
• Conductivity TDS Factor: Total Dissolved Solids (TDS) refers to the dissolved
inorganics in a solution. These dissolved inorganics will carry a current and
will be reflected as a conductivity reading. Since a relationship can be shown
between conductivity and TDS, a conductivity reading can be used as an
estimation of the presence of inorganics.
• The standard method of determining TDS (Total Dissolved Solids) is by
evaporating the sample to dryness at 180 ˚C and weighing the residue. After
evaporating the sample, one would have to calculate a specific “factor” for
the solution by taking the TDS value obtained in weighing and dividing it by
the conductivity of the sample. This factor would then be multiplied by the
subsequent conductivity readings to obtain the TDS value of the sample as
referenced in Standard Methods for Water and Wastewater.
• This Meter allows the operators to enter their own TDS factor for the
calculation of the TDS value in mg/L, with a selectable range from 0.01 to
10.00 and a default value of 0.49. The default value for TDS factor on the
meter is 0.49, which is a reasonable estimate of a TDS factor for natural
water applications.
• Auto-Calibration for conductivity uses a default cell constant to determine the
value of the conductivity standard. In order for the instrument to Auto-recognize
a conductivity standard it must know the cell constant within a factor of 3. So
the meter needs a nominal cell constant for the probe being used. If the real
cell constant was 1.0 then having an estimate of any value between 0.3 and 3.0
would be sufficient to determine which standard was being used and therefore
determine the standards temperature corrected value for calibration.
• The instrument Auto-recognizes Orion conductivity standards
1413 μS/cm,100 μS/cm, and 12.9 mS/cm only.
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