Hanna TDS meter calibration questions

[slimm]

dude, ppm is a numerical count of the total dissolved solids, period. its not about different scales or anything else. its about correctly calibrating your meter to give an accurate reading of the tds count. period.

I really think you should reconsider Hogdady.

Total dissolved solids (which are expressed in ppm) is not measured by these TDS meters. In fact they cannot measure TDS; all the meters can measure is Electrical Conductivity (EC) and use that to derive an approximated TDS ppm value. As manufacturers created these gadgets they failed to compare notes, and the methods they use to do this calculation do not all agree. Today, with meters like mine, you can simulate any one of the other meter standards by making an adjustment to the conversion factor. There are three conversion factors which various manufacturers use for displaying ppm's...

USA 1 ms/cm (EC 1.0 or CF 10) = 500 ppm
European 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
Australian 1 ms/cm (EC 1.0 or CF 10) = 700 ppm

When I went to buy my meter I had no idea that the measurement industry was so fragmented or I would have researched it more before I selected a meter. Not that I necessarily would have chosen a different one. Mine has a programmable conversion factor so I think I'm ok. I started this thread because I read a lot of on-line growing information and everyone is talking about the ppm of their solution. I would like to know - which scale should I use and how do I express / interpret TDS values when discussing with others?

[slimm]

Hogdady. From what I understand there is a true dissolved solids measurement that is absolute like you say, but taking that the measurement is more difficult than measuring EC and approximating TDS. If you want to know the true TDS value of a solution you can use the Gravimetric methods which involve evaporating and weighing the remaining solids. There are some problems with this method too since some of the dissolved solids may be volatile enough to evaporate with the water.

[Hogdady]

I really think you should reconsider Hogdady.

Total dissolved solids (which are expressed in ppm) is not measured by these TDS meters. In fact they cannot measure TDS; all the meters can measure is Electrical Conductivity (EC) and use that to derive an approximated TDS ppm value. As manufacturers created these gadgets they failed to compare notes, and the methods they use to do this calculation do not all agree. Today, with meters like mine, you can simulate anyone of the other meter standards by making an adjustment to the conversion factor. There are three conversion factors which various manufacturers use for displaying ppm's...

USA 1 ms/cm (EC 1.0 or CF 10) = 500 ppm
European 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
Australian 1 ms/cm (EC 1.0 or CF 10) = 700 ppm

When I went to buy my meter I had no idea that the measurement industry was so fragmented or I would have researched it more before I selected a meter. Not that I necessarily would have chosen a different one. Mine has a programmable conversion factor so I think I'm ok. I started this thread because I read a lot of on-line growing information and everyone is talking about the ppm of their solution. I would like to know - which scale should I use and how do I express / interpret TDS values when discussing with others?

I entirely understand what you are saying, but you are missing my point entirely. Isn't the function of your meter to give you a reasonably accurate reading of the parts per million of total dissolved solids in whatever you are measuring? YES! That's the only reason we have the damn thing. If there are different conversion factors, blah, blah, blah, and the end result is an accurate representation of the ppm, then it's only how we get there thats up for discussion.

[slimm]

I just came across a thread on this subject at another site and the recommendation there when reporting your PPM in a thread to give the conversion factor your meter uses for example 550 PPM @.7 or give the reading in EC which is the same meter to meter.

[slimm]

I entirely understand what you are saying, but you are missing my point entirely. Isn't the function of your meter to give you a reasonably accurate reading of the parts per million of total dissolved solids in whatever you are measuring? YES! That's the only reason we have the damn thing. If there are different conversion factors, blah, blah, blah, and the end result is an accurate representation of the ppm, then it's only how we get there thats up for discussion.

Exactly, so if you are running a meter on the Hanna scale and my meter was designed to use the Truncheon scale we have to find a way to normalize our values so we are talking apples to apples. We can do that by always reporting values in EC or by somehow communicating the conversion factor of our respective meters.

[Hogdady]

Exactly, so if you are running a meter on the Hanna scale and my meter was designed to use the Truncheon scale we have to find a way to normalize our values so we are talking apples to apples. We can do that by always reporting values in EC or by somehow communicating the conversion factor of our respective meters.

I guess I don't follow. I thought that if my meter told me that my solution had 1000 ppm, then it had 1000 ppm (within accuracy tolerances). If I used my micrometer to measure the thickness of a item and if I told you the thickness in millionths of an inch, than if you measured it with your micrometer, it should be the same. I shouldn't have to tell you that my micrometer is a Starett, only that the measurement is whatever.

[slimm]

I understand, it is confusing. I had this discussion at the hydro shop and everyone, including the customers in the store and the staff had different pictures about how this works. It is a mess, although at least we have conversion factors to help us normalize the values. So I would not need to know your meter manufacturer, just your conversion factor as illustrated in post #19 above.

[Hogdady]

I'm not saying that I'm confused with ec/tds/ppm conversion, I'm saying that I'm confused with your rationale. If I am using the conversion factor appropriate for my meter, then when I see a ppm value on the meter, that is the approximate ppm of the solution! If I tell you what my ppm is, you don't need to know a conversion factor or anything else. The meter does all of the work!

[slimm]

I'm sorry hogdady but you are still missing something. This is just like temperature. If we both go outside, in the same location, on a day where the temperature has just dipped to freezing and we measure the temperature we will get vastly different results, even though both of our thermometers were just calibrated. You will get a reading of 32 degrees and I will get a reading of 0 degrees. This is possible because just like the TDS meters there are different ways to calculate temperature - different linear scales: centigrade and fahrenheit. So you must report 32 degrees fahrenheit for the value to be meaningful.

Likewise when measuring TDS we have the same problem. When someone reports a ppm value one has to know whether they are talking about Hanna, Eutech or Truncheon scales.

Personally I think we should all switch over to reporting TDS values in EC. That way there is no ambiguity. I hope this helps. If not you can go here to learn more. I wish I had known about this link before I opened this thread =)

[Hogdady]

Slimm, I gotta take my hat off to ya. Not many people would have the patience nor intellect that you have shown in discussing this topic with me. I see exactly what you are saying, and that is essentually that ppm values are bogus. If there are different conversion factors then the same ec could be converted to different ppm values, based on the meter manufactures choice. Thanks Slimm, you have opened my eyes!

[slimm]

Thanks - I'm glad we both understand it now!

[Tulip]

I applaud, respect and honor both of you. + REP to both you!

I'm too stoned to get that technical! LOL

[lookoutfarms]

okay, correct me if i am wrong but when you calibrate the meter, either by the factory setting which has the conversion factor encoded on a chip then they have to find a STANDARDIZED SOLUTION...that is where it becomes apples to apples...you cannot use say a bottle of Hanna 1413 microsiemens/cm NACl to calibrate an Oakton Ultra basic which uses a different standard of calibration solution...which is a 1400 ppm solution, in other words, what they program into the damn things does not make a diff, it is when it is calibrated and what it is calibrated to that brings everyones ppm's to where you can consistently look at a nute program and take for instance Technafloras Recipe for success....the bloom mix comes up to ~1400...not 1400 on a hanna but 1200 on a bluelab or whatever....okay? correct me if i am wrong and i will send back my degree.

[Hogdady]

I had a problem with this concept as well. EC is the constant. All TDS meters convert EC to PPM's by their own conversion factor.



So the PPM values are only comparable if you know the conversion factors of the meters in use. This is why it is important to discuss TDS values in EC rather than PPM. The thread below is an excellent read...


What is the difference between ppm and EC?

[Maer]

The other thing to note about meters is they only measure ionic solids (salts) something like an alcohol or oil will not register because it does not increase EC.