Using a multimeter to calculate TDS

[Chadwick405]

I was doing a little research and found that a TDS meter works by measuring the conductivity of water. I would venture to say that you could use a multimeter to be able to know if you need to change filters in your RO/DI unit. Also from reading another forum that was for gardening a guy did a calculation that said as long as the leads are placed 1cm apart take the measured impedance and take the inverse of it and divide it by 0.000001, this is the electrical conductivity. Take this and multiply it by 500 which is the conversion factor for NaCl, which they usually use as the standard salt for conductivity calibrations.

 

Example @ 1cm

 

400k ohms : (1/400000 ohms) = 0.0000025 siemens, (0.0000025/0.000001) = 2.5*500 = 1250

 

800k ohms : (1/800000 ohms) = 0.00000125 siemens, (0.00000125/0.000001) = 1.25 *500 = 625

 

This would make sense since the impedance would climb as the water was more pure, pure water should not be able to conduct any electricity.

 

I am not sure if this would work, but its just an idea.

[kgross]

I was doing a little research and found that a TDS meter works by measuring the conductivity of water. I would venture to say that you could use a multimeter to be able to know if you need to change filters in your RO/DI unit. Also from reading another forum that was for gardening a guy did a calculation that said as long as the leads are placed 1cm apart take the measured impedance and take the inverse of it and divide it by 0.000001, this is the electrical conductivity. Take this and multiply it by 500 which is the conversion factor for NaCl, which they usually use as the standard salt for conductivity calibrations.

 

Example @ 1cm

 

400k ohms : (1/400000 ohms) = 0.0000025 siemens, (0.0000025/0.000001) = 2.5*500 = 1250

 

800k ohms : (1/800000 ohms) = 0.00000125 siemens, (0.00000125/0.000001) = 1.25 *500 = 625

 

This would make sense since the impedance would climb as the water was more pure, pure water should not be able to conduct any electricity.

 

I am not sure if this would work, but its just an idea.

 

I don't know if your math is correct, but this will work, the problem is though you need to build a jig to hold the probes correctly, and I think by the time you build the jig, $20 for a tds meter is not that bad..

 

Kim

[Gvtv44]

And it would be a good idea to test the idea next to a TDS

 

It could make sense if you had the stuff already.

[Chadwick405]

I just ordered one from from eBay, I will defiantly check it vs. the multimeter.

[Rocket]

*trying this now

[Rocket]

Well I feel I may have messed something up but I got a TDS multimeter reading of 100 for my RO/DI system

 

and 250TDS from my filtered and softened well water.

 

From my quick experiment I tried to repeat the RO/DI water test again and got totally different impedance numbers. And They would not stabilize. I feel I cannot conclude because I believe with such high impedance of RO/DI water that my meter could not read a measurement and was "freaking out."

 

The test on the well water was repeated with same results and a stable reading. So This might in fact work. I just need a better meter. But its a craftsman professional.

 

I'll try again tomorrow.