TDS conversion factor question

Hello,

I have a question thats been frustrating me to find an answer so i thought I'd ask it on here. I have a oakton waterproof tds meter. What is the diference between the tds factor and the ppm. If during calibration i calibrate it to the correct ppm does it matter what the tds factor is?

You'll want to use the same conversion factor as the source you are comparing to in order to be accurate. Or you can just go by EC if that's an option on your meter and not worry about conversion factors.

But in any case, conversion factor does matter when comparing ppm readings. In hydroponics, two different conversion factors being used can differ by as little as 50'ish ppm to 500+ ppm.

theres no ec setting on my tds meter

TDS us a reading if PPM which is a conversion of EC.

The three conversion factors are .5 .64 and .7



As you can see an EC of 1.0 @ .5 conversion factor is 500ppm,and an EC of 1.0 @ .64 conversion factor is 640ppm,and an EC of 1.0 @ .7 conversion is 700ppm.

I believe Oaktons work on a .5 conversion factor.

thanks for the answer, my next question is what is NaCl, KCI, and 442?

Sodium Chloride - table salt
Potassium Chloride
442 Oldsmobile? Lol got me there.

442 standards are formulated from sodium sulfate, sodium bicarbonate and sodium chloride in the ratio of 4:4:2 respectively.

Click to expand...

The 442 is probably the closest you'll get to a nutrient solution used in hydroponics.

The different standards (NaCl, KCI, and 442) are how they come up with the conversion factor to use on the EC reading your meter takes. The only way to truly get a TDS reading is to take a solution, evaporate off the water, and weigh the remaining solids that are left behind... So they did that with NaCl, KCI, and 442 solutions, as well as take EC readings, find the true TDS by weight, and then extrapolate how the EC reading compared to the true TDS in ppm for use in any type of solution. It's not super accurate because we don't grow in NaCl, KCI, or 442 solutions but it's close enough.

so NaCl is .5
and KCl is .53
and "442" is .725 right?

kngblnk said:

so NaCl is .5
and KCl is .53
and "442" is .725 right?

Click to expand...

Yeah that looks generally right @ around 1 EC (there's some variance for temperature, called temperature compensation applied with most meters). Stole this from Eutech's site (sorry can't fix the formatting of the table but the "ppm Value" and "Factor" column headers should be shifted over to the right by one colum):

[TABLE="width: 100%"]
[TR]
[TD="width: 15%"]Conductivity
at 25 [SUP]o[/SUP]C[/TD]
[TD="colspan: 2, align: center"]TDS KCl[/TD]
[TD="colspan: 2, align: center"]TDS NaCl[/TD]
[TD="colspan: 2, align: center"]TDS 442[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]ppm Value[/TD]
[TD="width: 12%, align: center"]Factor[/TD]
[TD="width: 15%, align: center"]ppm Value[/TD]
[TD="width: 12%, align: center"]Factor[/TD]
[TD="width: 16%, align: center"]ppm Value[/TD]
[TD="width: 17%, align: center"]Factor[/TD]
[/TR]
[TR]
[TD="width: 15%"]84 µS[/TD]
[TD="width: 13%, align: center"]40.38[/TD]
[TD="width: 12%, align: center"]0.5048[/TD]
[TD="width: 15%, align: center"]38.04[/TD]
[TD="width: 12%, align: center"]0.4755[/TD]
[TD="width: 16%, align: center"]50.50[/TD]
[TD="width: 17%, align: center"]0.6563[/TD]
[/TR]
[TR]
[TD="width: 15%"]447 µS[/TD]
[TD="width: 13%, align: center"]225.6[/TD]
[TD="width: 12%, align: center"]0.5047[/TD]
[TD="width: 15%, align: center"]215.5[/TD]
[TD="width: 12%, align: center"]0.4822[/TD]
[TD="width: 16%, align: center"]300.0[/TD]
[TD="width: 17%, align: center"]0.6712[/TD]
[/TR]
[TR]
[TD="width: 15%"]1413 µS[/TD]
[TD="width: 13%, align: center"]744.7[/TD]
[TD="width: 12%, align: center"]0.5270[/TD]
[TD="width: 15%, align: center"]702.1[/TD]
[TD="width: 12%, align: center"]0.4969[/TD]
[TD="width: 16%, align: center"]1000[/TD]
[TD="width: 17%, align: center"]0.7078[/TD]
[/TR]
[TR]
[TD="width: 15%"]1500 µS[/TD]
[TD="width: 13%, align: center"]757.1[/TD]
[TD="width: 12%, align: center"]0.5047[/TD]
[TD="width: 15%, align: center"]737.1[/TD]
[TD="width: 12%, align: center"]0.4914[/TD]
[TD="width: 16%, align: center"]1050[/TD]
[TD="width: 17%, align: center"]0.7000[/TD]
[/TR]
[TR]
[TD="width: 15%"]8974 µS[/TD]
[TD="width: 13%, align: center"]5101[/TD]
[TD="width: 12%, align: center"]0.5685[/TD]
[TD="width: 15%, align: center"]4487[/TD]
[TD="width: 12%, align: center"]0.5000[/TD]
[TD="width: 16%, align: center"]7608[/TD]
[TD="width: 17%, align: center"]0.8478[/TD]
[/TR]
[TR]
[TD="width: 15%"]12,880 µS[/TD]
[TD="width: 13%, align: center"]7447[/TD]
[TD="width: 12%, align: center"]0.5782[/TD]
[TD="width: 15%, align: center"]7230[/TD]
[TD="width: 12%, align: center"]0.5613[/TD]
[TD="width: 16%, align: center"]11,367[/TD]
[TD="width: 17%, align: center"]0.8825[/TD]
[/TR]
[TR]
[TD="width: 15%"]15,000 µS[/TD]
[TD="width: 13%, align: center"]8759[/TD]
[TD="width: 12%, align: center"]0.5839[/TD]
[TD="width: 15%, align: center"]8532[/TD]
[TD="width: 12%, align: center"]0.5688[/TD]
[TD="width: 16%, align: center"]13,455[/TD]
[TD="width: 17%, align: center"]0.8970[/TD]
[/TR]
[TR]
[TD="width: 15%"]80 mS[/TD]
[TD="width: 13%, align: center"]52,168[/TD]
[TD="width: 12%, align: center"]0.6521[/TD]
[TD="width: 15%, align: center"]48,384[/TD]
[TD="width: 12%, align: center"]0.6048[/TD]
[TD="width: 16%, align: center"]79,688[/TD]
[TD="width: 17%, align: center"]0.9961[/TD]
[/TR]
[/TABLE]