PPM Conversion Factors
Not all TDS meters will give the same PPM reading. The main reason for this is that different meters will use different conversion factors. These conversion factors are based off the EC reading. For example: A meter that uses a conversion factor of 0.5 will display a reading of 0.5 times that of the EC reading. If the EC reading is 1000 µS then the ppm reading will be 500 ppm. It is as simple as multiplying 1000 by the conversion factor of 0.5. If the meter uses a conversion factor of 0.7 (the most common conversion factor used) then 1000 µS would be 700 ppm (1000 x 0.7). When purchasing a TDS meter it is very important to find out what the correct conversion factor is for the meter. It could make a difference of more than 200 ppm! Not only is it important to know what the conversion factor for the meter is, it is also important to know the conversion factor of the calibration solution. Generally speaking, Genesis calibration solutions are for meters that use a 0.7 conversion factor and the Hanna solutions are for meters with a 0.5 conversion factor.