EC to salinity ppm

[ramarro123]

Hello,

i am building and playing with an arduino to do some DIY monitor stuff

with a EC probe, i am able to measure mS/cm conductivity, but i am having trouble converting it to salinity in ppm.

i have checked this article
http://www.reefkeeping.com/issues/2004-06/rhf/

that have this nice table

34->51.7
35->53.0
36->54.4


with the relation of ppm -> conductivity
wonder if there is a formula to convert the conductivity to ppm


with lagrange regression polynomial formula i found that one
y = 5.000000008·10-2 x2 - 2.149999998 x + 66.99999976
or this one (for a cubic regression)
y = -3.333339188·10-2 x3 + 3.550006032 x2 - 124.6168861 x + 1495.002808

they are very close, and i will probably use one of this one, but in case you
have the correct one, i will really appreciate to know it


sorry for my bad english

 

[bertoni]

For our hobbyist purposes, the scales can be treated as linear over the relevant range. Multiplying the conductivity by 0.66 should be close enough. If you want to be able to read a wide range, you might have more work to do.