Diy tds meter calibration

Cory · Nov 11, 2015

I think i need to calibrate my hm tds meter for my ro/di. New pack of dion resin is reading 005ppm, so it must be out.

Can someone tell me how many g of salt in how much water? Here is what they say:

http://www.tdsmeter.com/calibration_maintenance.html

JimWelsh · Nov 11, 2015

Assuming that by "PPM" they mean w/v, the units are mg/L, so the "342 ppm NaCl" calibration standard would be 342 mg of NaCl per 1 liter of water. In other words, 0.342 g NaCl in 1 L H2O.

Cory · Nov 11, 2015

What about a smaller amount instead of 1 liter? Id like to use my scale .001x 500g

Randy Holmes-Farley · Nov 11, 2015

I'd be surprised if 0 ppm TDS water could read 5 ppm TDS no matter the calibration, because the 0 ppm point is fixed and only the slope is changed by calibration.

Does it read 0 ppm in air but 5 ppm in the RO/DI water?

You can use a smaller amount and make less, but you'll introduce more error. As it is, to make a liter you only use 0.342 g of salt. What's wrong with that?

If you want to divide it by ten to 0.034 g and make 100 mL, that's OK, but again, I expect your scale can read more accurately on 0.34 g than on 0.034 grams.

TheEngineer · Nov 11, 2015

You can buy the solution from your LFS for like $2.

Cory · Nov 11, 2015

My lfs doesnt sell it.

I can weigh it for 1 liter. But my scale is only 500g. Does 1 liter of pure water weigh 1000g? I could weigh it 3 times i guess.

I have the hm dual tds reader for ro/di. One of them reads 001. And the other reads 005. Both read 000 when out of water. Im wondering if i broken it by dropping it a few times lol.

JimWelsh · Nov 11, 2015

Get yourself a Class A 1000 mL volumetric flask. Together with it and your scale, you'll be able to make up some very accurate solutions of lots of things!

Cory · Nov 11, 2015

Im happy to have lab stuff in the house for the tank! Well see this pay if i can spare some cash for the flask, nist thermometer and hydrometer.

Randy Holmes-Farley · Nov 11, 2015

Weight out 400 grams twice for the water

Then weigh out 274 mg of salt to get to the 342 ppm solution.

however, you can really make any solution you want for such a calibration.

Cory · Nov 11, 2015

So would i adjust the meter to read 342 or 003?

And iodized table salt is fine?

Randy Holmes-Farley · Nov 11, 2015

Iodized won't make a noticeable difference. Adjust it to 342 ppm TDS.

Cory · Nov 13, 2015

Randy Holmes-Farley said:
Weight out 400 grams twice for the water

Then weigh out 274 mg of salt to get to the 342 ppm solution.

however, you can really make any solution you want for such a calibration.

So i did this and placed it back in the water i made with the ro/di and it was 003 instead of 005. However i made it with the same ro/di and put in 274 mg of salt but i turned the calibration dial to read 274ppm... So i messed up and got to do it again.

You think its broken? Should i buy some distilled water for it?

Randy Holmes-Farley · Nov 13, 2015

274 mg of salt in what? The 800 g of water?

Does it read 0 ppm TDS in air?

Why are you certain your RO/DI is 0 ppm TDS?

Cory · Nov 13, 2015

Randy Holmes-Farley said:
274 mg of salt in what? The 800 g of water?

Does it read 0 ppm TDS in air?

Why are you certain your RO/DI is 0 ppm TDS?

Yes in the 800g of water. Im actually not certain, but how would you know? The membrane is about 2 years old. Never back flushed. But it was reading 160 for tap, 360 for discharge and 005 for after ro membrane, after deion 005 (new bag).

Randy Holmes-Farley · Nov 13, 2015

You sure the DI is hooked up right?

And, does the meter read zero in air?

Cory · Nov 13, 2015

Im pretty sure the deion is hooked up right, as its just the ro water that enters a separate canister. When i put the new media in i tapped it hard to pack it in.

It does read zero in air.

The wife made some today, and now the ro only water was reading 000. Strange?

Randy Holmes-Farley · Nov 14, 2015

Cory said:
Im pretty sure the deion is hooked up right, as its just the ro water that enters a separate canister. When i put the new media in i tapped it hard to pack it in.

It does read zero in air.

The wife made some today, and now the ro only water was reading 000. Strange?

Seems clear to me: she does a better job with it.

Cory · Nov 14, 2015

Lol she just needs to be better at cooking.

But really ro water should never read zero right? After deion it should read zero. Do You think soemthing is wrong with the tds meter?

Randy Holmes-Farley · Nov 14, 2015

Cory said:
Lol she just needs to be better at cooking.

But really ro water should never read zero right? After deion it should read zero. Do You think soemthing is wrong with the tds meter?

Right, although RO only water might read zero if the input to it is low enough (say, less than 50 ppm)

I would not assume that there is anything wrong with the meter.