Multimeter as a tds meter... perhaps

I think that it would be feasible that if one had a good multimeter, it would be possible to tell the ppm and EC of a nutrient solution or even tap water after receiving the impedance (resistance) readings and using a little math. Starting with the electrodes exactly (or as exact as one might get the electrodes) one cm apart we stick the electrodes into solution very quickly and wait until we have a semi stable measurement (you can see a pattern in how the numbers increase) and then pull them out as to cause as little degradation of the electrodes as possible and to make an attempt at keeping net ion movement to a minimum (hopefully +/- 1 ohm accuracy). now we have an number in K ohm or ohm. Conductivity = 1 / R so divide one by the resistance. This will give us a measurement in Siemens/meter so... hopefully the number will be similar to the EC reading if you divide by 0.000001. Multiplying by 500 (conversion factor for NaCl calibration) should give a TDS type reading (hopefully). The deviation caused by the temp can maybe be figured out by replacing R with R(T)--- > R(T) = R1 [1+alpha(T-Tr)] where R1 is the resistance (ohm) at T or the temperature of the reservoir and Tr is a reference temp. which should be specified by alpha (oh yeah... everything has to be done in Celsius) I'm not sure yet. Unfortunately one should not yet do these calculations as we are missing the alpha. If this interests you please help me with this part. Alpha here is used to denote resistance change per deg c also it is said to be linear. So if you wanted to try to help this is kinda hard to do, but Measure the temp as exactly as you can and the measure the resistance as fast as you can and do it as many times as it entertains you. Generally 4-10 data points would be nice to have (one of which is at room temp). Alpha will be different for everyone. Unfortunately my Multimeter is crap and I haven't gotten around to getting a better one yet, so if someone finds this interesting again, please try it just keep in mind that this is very theoretical.
also just if anyone might wonder conversion to ohm from k ohm is k ohm*1000.

ok so this is a cool bit of math, i would surgest if some one wanted to find alfa, that they make a simple holder for the electrodes eg an eraser with a couple holes drill one centermeter apart and that they use a comon and readly avalible substance eg flat coke, so ppl can cross reference there test reults... this could ave a fortune for many good stuff hope its a winner

n4alpaca said:

I think that it would be feasible that if one had a good multimeter, it would be possible to tell the ppm of a nutrient solution after receiving the resistance readings and using a little math of course. Starting with the electrodes exactly (or as exact as one might get the electrodes) one cm apart we stick the electrodes into solution very quickly and wait until we have a measurement and then pull them out as to cause as little degradation of the electrodes as possible and to make an attempt at keeping net ion movement to a minimum (hopefully +/- 1 ohm accuracy). now we have an number in ohm. Conductivity = 1 / R so divide one by the resistance. This will give us a measurement in Siemens/meter so... hopefully the number will be similar to the EC reading if you divide by 0.000001 and then multiply by 500 (conversion factor for NaCl calibration). The deviation caused by the temp can maybe be figured out by replacing R with R(T)--- > R(T) = R1 [1+alpha(T-Tr)] where R1 is the resistance (ohm) at T or the temperature of the reservoir and Tr is a reference temp. which should be specified by alpha (oh yeah... everything has to be done in Celsius) I'm not sure yet. Unfortunately one should not yet do these calculations as we are missing the alpha. If this interests you please help me with this part. Alpha here is used to denote resistance change per deg c also it is said to be linear. So if you wanted to try to help this is kinda hard to do, but Measure the temp as exactly as you can and the measure the resistance as fast as you can and do it as many times as it entertains you. Generally 4-10 data points would be nice to have (one of which is at room temp). Alpha will be different for everyone. Unfortunately my Multimeter is crap and I haven't gotten around to getting a better one yet, so if someone finds this interesting again, please try it just keep in mind that this is very theoretical.
also just if anyone might wonder conversion to ohm from k ohm is k ohm*1000.

Click to expand...

This is way out of my league, but props...

Bumpbumpbump

I'm surprised only 2 people are as syked as I am about this.

No one with an EC meter, tds meter and semi decent multimeter wants to help?

im still waiting on gear for my first hydro grow but i think ill test it but keeping running records of both way of mesureing

so do you think it would be posible to mesure ph with a multimeter? im not sure how eletronic ph meter work so....

read, this made me very happy, it may make you happy as well

http://en.wikipedia.org/wiki/PH_meter

I'm ordering a decent multimeter as we speak. unfortunately I don't have any means of measuring tds ill make a guess at what the ppm and EC should be for my town. Back the the pH meter thing... that would be really cool and now that I think about it definitely possible (they have a temp reader too its called a thermocouple).

this would be remarkable if a multimeter could do everything... which it probably could... mainly because all of the readings from pH and ec meters are based on certain properties of electrical current so small adjustments and you can most likely do everything.

also this is cool


http://www.66pacific.com/ph/simplest_ph.aspx (you have to copy paste the link)
someone did the work for us, so looks like a multimeter is the most efficient tool available.

ill be gone for a week, so ill post again in a week.