Owner's manual

4948
13. Appendix 2: Calculating TDS Conversion Factors
You can calibrate your meter using TDS calibration standard solutions. The calibra-
tion standard only needs to give the TDS value at a standard temperature such as
25°C. To determine to 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 a standard you make using
high purity water and precisely weighed salts.
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; if the TDS value is in ppt the conductivity value must be in mS.
Check your factor by multiplying the conductivity reading by the factor in the above
formula. The result should be the TDS value.
12. Appendix 1: Conductivity to TDS Conversion Factors
1. Factor—the conductivity to ppm TDS conversion factor. Multiply conductivity by this factor to get ppm TDS for the type of TDS
reading needed.
2. 442—a formulation that most closely represents the conductivity to ppm relationship, on average, for naturally occurring fresh
water.
3. TDS Your Material—These columns are for you to write in your application-specific conductivity-to-ppm values and conversion
factors for future reference.
Factor = actual TDS ÷ Actual Conductivity @ 25°C
C
onductivity
TDS KCl TDS NaCl TDS 442
2
TDS Your Material
3
at 25°C
ppm Factor
1
ppm Factor
1
ppm Factor
1
ppm Factor
Value Value Value Value
84 µS 40.38 0.5048 38.04 0.4755 50.50 0.6563
447 µS 225.6 0.5047 215.5 0.4822 300.0 0.6712 1413 µS 744.7 0.5270 702.1 0.4969 1000 0.7078 1500 µS 757.1 0.5047 737.1 0.4914 1050 0.7000
8974 µS 5101 0.5685 4487 0.5000 7608 0.8478
12880 µS 7447 0.5782 7230 0.5613 11,367 0.8825 15000 µS 8759 0.5839 8532 0.5688 13,455 0.8970 80 mS 52,168 0.6521 48,384 0.6048 79,688 0.9961
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