Is it possible to make my own TDS calibration solution?

[weblance]

I have a HM Digital TDS meter: http://www.tdsmeter.com/products/tds3.html and it needs to be calibrated. Since I live in Denmark the right calibration solution (http://www.tdsmeter.com/products/calibrationsolution.html) is very hard to get.

Is it possible for me to make my own solution? I'm thinking of using this formula:

1 mg NaCl/liter of distilled water = 1 ppm TDS

Am I right or can't this be used? If I'm right - where can I get NaCl, is it just regular table salt or can I get it at a pharmacy?

Thanks in advance!

/Carl

 

[Randy Holmes-Farley]

In general, if you use the TDS meter to monitor RO/DI devices, it isn't normally necessary to calibrate.

Yes, IMO you could use table salt to make a standard. The two ways would be with a good scale and small amount of table salt in DI water, or a larger amount measured by teaspoon that you lowered in TDS by serial dilution. I have not worked out details of the latter however.

What range of TDS does your meter cover?

 

[weblance]

The range is 0 - 9990 ppm (mg/L)

 

[weblance]

I think that it needs to be calibrated. It reads 1 ppm on the RO water, and 1 ppm is pretty low even for a RO unit.

 

[weblance]

Then the calculation should be: 342 ppm TDS = 342 mg of salt + one liter of distilled water

 

[Randy Holmes-Farley]

Yes, if you can measure out that amount, that should be an adequate way to calibrate the meter.

The weight measurement error will be smaller if you use a larger amount, and calibrate at, say 5,000 ppm (= 5 g/L).

 

[weblance]

There is iodine in table salt . . . woun't that affect the reading?

 

[Randy Holmes-Farley]

No, it is not enough to be significant, although you can get table salt without it. The other ingredients also should not be a problem, since we are not expecting or needing to be closer than +/- 10% (or more).

 

[weblance]

OK thanks Randy !
I'll wisit my local pharmacy Monday to get some distilled water.

 

[Randy Holmes-Farley]

You're welcome.

Good luck and let us know how it works out.

 

[Hobster]

<a href=showthread.php?s=&postid=6769589#post6769589 target=_blank>Originally posted</a> by Randy Holmes-Farley
Yes, if you can measure out that amount, that should be an adequate way to calibrate the meter.

The weight measurement error will be smaller if you use a larger amount, and calibrate at, say 5,000 ppm (= 5 g/L).

I am interested in this also. I have the same meter. I wanted to verify mine as I had a defective RO membrane. It is next to impossible to find a calibration soultion that is 342 ppm.

How much is 5 grams of say Morton Salt in teaspons?
Is store bought distilled water actually "0"ppm?

As of today my ro/di is reading 0 ppm so I could use that and how ever much salt in a liter??

 

[Randy Holmes-Farley]

Does it really need to be 342 ppm?

 

[Hobster]

No, I do not think so. That's just what the web site above says their calibration solution is. I last used a packet conductivity solution of 10 micro something
My tap water is about 342ppm.

Now that I think about it, if my meter is reading "0" and calibrated to the 10. Can I just mix a trace amount of salt in a bottle of RO/DI and whatever ppm that comes to, use that as a check or standard? It shouldn't change over time if sealed will it?

If we estimate the amount of Morton of salt to add to a liter of RO/DI to get somewhere close say 300 to 500 ppm that would be
at least be in the ball park.

 

[Randy Holmes-Farley]

As long as your believe it is calibrated, then yes, it is trivial to make your own standard from DI water and some table salt. Good point!