When reporting your PPM in a thread, please give the conversion factor your meter uses. The more data points that you use, the closer you will be to finding your true conversion factor The answer is your meter’s convertion factor and should be a number between 0.50 and 0.72 To improve accuracy, take ec and ppm readings from your res daily for about ten days. [Note: ms must be converted to us: One millisiemen = 1000 microsiemens (1.0 ms/cm = 1000.0 us/cm) Change to EC on the meter and read EC in ms/cm. Place the probe in the solution and read TDS in ppm. If your meter allows you to switch between EC and TDS units, your conversion factor can be easily determined by dividing one by the other. There are three conversion factors which various manufacturers use for displaying ppm’s.Įuropean 1 ms/cm (EC 1.0 or CF 10) = 640 ppmĪustralian 1 ms/cm (EC 1.0 or CF 10) = 700 ppm Calculating the conversion factor
All ppm (TDS, Total Dissolved Solids) pens actually measure in EC or CF and run a conversion program to display the reading in ppm’s. So again, the problem is that different ppm pen manufacturers use different conversion factors to calculate the ppm they display. * All ppm pens actually measure the value based on EC and then convert the EC value to display the ppm value, having different conversion factors between differing manufacturers is why we have this problem communicating nutrient measurments between one another.ĮC is measured in millisiemens per centimeter (ms/cm) or microsiemens per centimeter (us/cm).ĮC and CF (Conductivity Factor) are easily converted between each other. 72, *depending on the meter manufacturer, which do a good job of approximating a TDS calculation from the meter’s measurement of EC. The meter uses an approximate conversion factor, because the exact composition of the mix is not known. Everyone’s nutrient mix is different, so no factor will be exact. The meter cannot directly measure TDS as described above, and instead uses a linear conversion factor to calculate it. A siemens is also called a mho (ohm backwards).įor convenience, EC measurements often are converted to TDS units (ppm) by the meter. It is the reciprocal of the ohm, the standard unit of electrical resistance. A material has a conductance of one siemens if one ampere of electric current can pass through it per volt of electric potential. The greater the quantity of nutrient ions in a solution, the more electricity that will be conducted by that solution. EC is a measurement of all those charges in the solution that conduct electricity. Nutrient ions have an electrical charge, a whole number, usually a positive or negative 1, 2, or 3. It can be determined with an inexpensive hand held meter. Example: 50 mL of the 700ppm solution would leave 35 mg of salt at the bottom of a crucible after drying.Įlectrical Conductivity (EC) is expressed in siemens per centimeter (s/cm) or milliseimens per centimeter(ms/cm). This type of measurement requires accurate liquid measurement, glassware, a drying oven, and a milligram balance. To accurately calculate total dissolved solids (TDS), one would evaporate a measured filtered sample to dryness, and weigh the residue.
A solution of nutrients dissolved in water at a strength of 700 ppm means that there are 700 milligrams if dissolved solids present for every liter of water. It is a measurement of mass and determined by weighing, called a gravimetric analysis. Total dissolved solids (TDS) is typically expressed in parts per million (ppm). To estimate TDS, one can use a meter that measures the Electric Conductivity (EC) of a solution, and convert the number to TDS in parts per million (ppm). Total Dissolved Solids (TDS) is the best measurement of the nutrient concentration of a hydroponic solution.
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