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11
Calculating TDS Conversion Factor
You can calibrate your meter using TDS calibration standard solutions.
The calibration standard only needs to give the TDS value at a standard
temperature such as 25°C. To determine the conductivity-to-TDS conversion
factor use the following formula:
Factor = Actual TDS ÷ Actual Conductivity @ 25°C
Actual TDS: Value from the solution bottle label or as a standard
you make using high purity water and precisely weighed salts.
Tip: ppm = milligram of salt(s) per litre of water
Actual Conductivity: Value measured using a properly calibrated
Conductivity/Temperature meter.
Both the Actual TDS and the Actual Conductivity values must be in the same
magnitude of units. For example, if the TDS value is in ppm the conductivity
value must be in µS/cm; if the TDS value is in ppt the conductivity value must
be in mS/cm.
Check your factor by multiplying the conductivity reading by the factor
in the above formula. The result should be in TDS value.
Tip: When the TDS factor is set to 1.0, Conductivity = TDS.
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