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APPENDIX 2: CALCULATING The TDS CONVERSION FACTOR
The meter can be calibrated using TDS calibration standard solutions. The
TDS value of the solution at a standard temperature, such as 25 °C, is required.
To determine the conductivity-to-TDS conversion factor use the following
formula:
Factor = Actual TDS ÷ Actual Conductivity @ 25 °C
Definitions:
•Actual TDS: Value from the solution bottle label or as calculated when
prepared with high purity water and precisely weighed salts.
•Actual Conductivity: Value measured using a properly calibrated
Conductivity/Temperature meter.
Both the Actual TDS value 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; if the TDS value is in ppt the conductivity
value must be in mS.
The calculated factor can be checked by multiplying the conductivity reading
by the factor. The result should be the TDS value.
APPENDIX 3: CALCULATING TEMPERATURE COEFFICIENTS
To determine the temperature coefficient of the sample solution:
Where:
tc = Temperature coefficient
C
= Conductivity at Temp 1
T1
T
= Temp 1
1
NOTE: A controlled temperature water bath is ideal for this procedure.
1. Immerse the probe in the solution and adjust the temperature coefficient to
0% (that is, no compensation) by following instructions as described in
Temperature Coefficient.
25 = 25 °C
C
= Conductivity at Temp 2
T2
T
= Temp 2
2
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