sorry but that's not correct from what i've found
So, what is the difference between conductivity and TDS meters?
In pure scientific terms, conductivity tells you how well electricity is passing through a substance. On the other hand, TDS indicates the amount of dissolved solids within a liquid, accounting for both conductible and non-conductible particles.
In practice, when measuring conductivity and TDS both conductivity meters and TDS meters pass electricity through a liquid. In fact, conductivity meters are used to estimate the TDS in a substance.
How is this done? Simply, TDS meters measure conductivity, then apply a conversion factor. Even if your meter is a TDS-only meter and does not display conductivity it still uses electrical conductivity with a conversion factor to calculate the TDS results.
Why? Well, for a true TDS measurement you have to evaporate all the moisture from your sample, then weigh the solid residue. While this is the most accurate method, in practice it is often impractical.
In summary, there is a correlation between conductivity and TDS. They are not the same. TDS meters that use conductivity to generate measurements only estimate TDS
if they measure in 2 different units (siemens and parts per million) , they can't be the same thing. one is an estimation of the other.