EC/TDS/PPM What are the differences?
- Thread starter Paola
- Start date
mogie
Well-Known Member
Does this help?
Total Dissolved Solids (TDS) is the best measurement of the nutrient concentration of a hydroponic solution. To estimate TDS, one can use a meter that measures the Electric Conductivity (EC) of a solution, and convert the number to TDS in parts per million (ppm). Many meters will do this conversion.
Total dissolved solids (TDS) is typically expressed in parts per million (ppm). It is a measurement of mass and determined by weighing, called a gravimetric analysis. A solution of nutrients dissolved in water at a strength of 700 ppm means that there are 700 milligrams if dissolved solids present for every liter of water. To accurately calculate total dissolved solids (TDS), one would evaporate a measured filtered sample to dryness, and weigh the residue. This type of measurement requires accurate liquid measurement, glassware, a drying oven, and a milligram balance. Example: 50 mL of the 700ppm solution would leave 35 mg of salt at the bottom of a crucible after drying.
Electrical Conductivity (EC) is expressed in siemens per centimeter (s/cm) or milliseimens per centimeter(ms/cm). It can be determined with an inexpensive hand held meter. Nutrient ions have an electrical charge, a whole number, usually a positive or negative 1, 2, or 3. EC is a measurement of all those charges in the solution that conduct electricity. The greater the quantity of nutrient ions in a solution, the more electricity that will be conducted by that solution. A material has a conductance of one siemens if one ampere of electric current can pass through it per volt of electric potential. It is the reciprocal of the ohm, the standard unit of electrical resistance. A siemens is also called a mho (ohm backwards).
For convenience, EC measurements often are converted to TDS units (ppm) by the meter.
The meter cannot directly measure TDS as described above, and instead uses a linear conversion factor to calculate it. Everyone’s nutrient mix is different, so no factor will be exact. The meter uses an approximate conversion factor, because the exact composition of the mix is not known. Conversion factors range from .50 to .72, *depending on the meter manufacturer, which do a good job of approximating a TDS calculation from the meter’s measurement of EC.
* All ppm pens actually measure the value based on EC and then convert the EC value to display the ppm value, having different conversion factors between differing manufacturers is why we have this problem communicating nutrient measurments between one another.
EC is measured in millisiemens per centimeter (ms/cm) or microsiemens per centimeter (us/cm).
One millisiemen = 1000 microsiemens.
EC and CF (Conductivity Factor) are easily converted between each other.
1 ms/cm = 10 CF
"The communication problem"...
So again, the problem is that different ppm pen manufacturers use different conversion factors to calculate the ppm they display. All ppm (TDS, Total Dissolved Solids) pens actually measure in EC or CF and run a conversion program to display the reading in ppm's.
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
For example,
Hanna, Milwaukee 1 ms/cm (EC 1.0 or CF 10) = 500 ppm
Eutech 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
Truncheon 1 ms/cm (EC 1.0 or CF 10) = 700 ppm
Calculating the conversion factor
If your meter allows you to switch between EC and TDS units, your conversion factor can be easily determined by dividing one by the other.
Place the probe in the solution and read TDS in ppm. Change to EC on the meter and read EC in ms/cm.
Conversion factor = ppm / ec.
[Note: ms must be converted to us: One millisiemen = 1000 microsiemens (1.0 ms/cm = 1000.0 us/cm)
According to the chart below:
1.0 ms/cm = 500 ppm (USA Hanna)
1000 us/cm = 500 ppm
Conversion factor = ppm / (ms/cm * 1000)
.50 = 500ppm / (1000us/cm) ]
The answer is your meter's convertion factor and should be a number between 0.50 and 0.72 To improve accuracy, take ec and ppm readings from your res daily for about ten days. Average the conversion factors. The more data points that you use, the closer you will be to finding your true conversion factor.
When reporting your PPM in a thread, please give the conversion factor your meter uses. For example: 550 PPM @0.7 or give the reading in EC, which should be the same meter to meter.
It may also be advisable to give the starting value of your water; there is a huge difference between RO and distilled water with a PPM of approximately 0 and hard tap water of PPM 300 @.5 (notice the conversion factor so others can work out the EC) or well water with a conductance of 2.1 ms/cm.
A note to Organic Growers:
An EC meter has fewer applications for a soil grower because many organic nutrients are not electrically charged or are inert. Things like Superthrive or Fish Emulsion, blood meal, rock phosphate or green sand cannot be measured with a meter reliably when they are applied or in runoff. Meters can only measure electrically charged salts in solution.
Total Dissolved Solids (TDS) is the best measurement of the nutrient concentration of a hydroponic solution. To estimate TDS, one can use a meter that measures the Electric Conductivity (EC) of a solution, and convert the number to TDS in parts per million (ppm). Many meters will do this conversion.
Total dissolved solids (TDS) is typically expressed in parts per million (ppm). It is a measurement of mass and determined by weighing, called a gravimetric analysis. A solution of nutrients dissolved in water at a strength of 700 ppm means that there are 700 milligrams if dissolved solids present for every liter of water. To accurately calculate total dissolved solids (TDS), one would evaporate a measured filtered sample to dryness, and weigh the residue. This type of measurement requires accurate liquid measurement, glassware, a drying oven, and a milligram balance. Example: 50 mL of the 700ppm solution would leave 35 mg of salt at the bottom of a crucible after drying.
Electrical Conductivity (EC) is expressed in siemens per centimeter (s/cm) or milliseimens per centimeter(ms/cm). It can be determined with an inexpensive hand held meter. Nutrient ions have an electrical charge, a whole number, usually a positive or negative 1, 2, or 3. EC is a measurement of all those charges in the solution that conduct electricity. The greater the quantity of nutrient ions in a solution, the more electricity that will be conducted by that solution. A material has a conductance of one siemens if one ampere of electric current can pass through it per volt of electric potential. It is the reciprocal of the ohm, the standard unit of electrical resistance. A siemens is also called a mho (ohm backwards).
For convenience, EC measurements often are converted to TDS units (ppm) by the meter.
The meter cannot directly measure TDS as described above, and instead uses a linear conversion factor to calculate it. Everyone’s nutrient mix is different, so no factor will be exact. The meter uses an approximate conversion factor, because the exact composition of the mix is not known. Conversion factors range from .50 to .72, *depending on the meter manufacturer, which do a good job of approximating a TDS calculation from the meter’s measurement of EC.
* All ppm pens actually measure the value based on EC and then convert the EC value to display the ppm value, having different conversion factors between differing manufacturers is why we have this problem communicating nutrient measurments between one another.
EC is measured in millisiemens per centimeter (ms/cm) or microsiemens per centimeter (us/cm).
One millisiemen = 1000 microsiemens.
EC and CF (Conductivity Factor) are easily converted between each other.
1 ms/cm = 10 CF
"The communication problem"...
So again, the problem is that different ppm pen manufacturers use different conversion factors to calculate the ppm they display. All ppm (TDS, Total Dissolved Solids) pens actually measure in EC or CF and run a conversion program to display the reading in ppm's.
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
For example,
Hanna, Milwaukee 1 ms/cm (EC 1.0 or CF 10) = 500 ppm
Eutech 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
Truncheon 1 ms/cm (EC 1.0 or CF 10) = 700 ppm
Calculating the conversion factor
If your meter allows you to switch between EC and TDS units, your conversion factor can be easily determined by dividing one by the other.
Place the probe in the solution and read TDS in ppm. Change to EC on the meter and read EC in ms/cm.
Conversion factor = ppm / ec.
[Note: ms must be converted to us: One millisiemen = 1000 microsiemens (1.0 ms/cm = 1000.0 us/cm)
According to the chart below:
1.0 ms/cm = 500 ppm (USA Hanna)
1000 us/cm = 500 ppm
Conversion factor = ppm / (ms/cm * 1000)
.50 = 500ppm / (1000us/cm) ]
The answer is your meter's convertion factor and should be a number between 0.50 and 0.72 To improve accuracy, take ec and ppm readings from your res daily for about ten days. Average the conversion factors. The more data points that you use, the closer you will be to finding your true conversion factor.
When reporting your PPM in a thread, please give the conversion factor your meter uses. For example: 550 PPM @0.7 or give the reading in EC, which should be the same meter to meter.
It may also be advisable to give the starting value of your water; there is a huge difference between RO and distilled water with a PPM of approximately 0 and hard tap water of PPM 300 @.5 (notice the conversion factor so others can work out the EC) or well water with a conductance of 2.1 ms/cm.
A note to Organic Growers:
An EC meter has fewer applications for a soil grower because many organic nutrients are not electrically charged or are inert. Things like Superthrive or Fish Emulsion, blood meal, rock phosphate or green sand cannot be measured with a meter reliably when they are applied or in runoff. Meters can only measure electrically charged salts in solution.
VictorVIcious
Well-Known Member
BY jove I think hes got it. What did you decide to do about your electricity? VV
I'm going to stick with the 120v and split everything evenly over 2 different circuits. Going to pick up some hospital grade plugs and wall outlets as well.
jackinthebox
Well-Known Member
Mogie is so nice, she took the time to type all of that out for you : )
*wink wink)
*wink wink)
Haha.
flabbyone
Well-Known Member
Oh great and a friend just bought a TDS and of course it does not measure in EC, well, he is going to use it, once he figures out what it all means. He does not have a computer so I have to do all the typing. Sometimes I wonder if he really can type, but then I have seen him try, so....
I am going to start a new thread, I had asked his questions on your thread, sorry, I just edited to move my question instead of jumping on your thread.
Thanks and sorry for the Highjacking!
I am going to start a new thread, I had asked his questions on your thread, sorry, I just edited to move my question instead of jumping on your thread.
Thanks and sorry for the Highjacking!
charlesweedmore
Well-Known Member
great post ,thanks
Mr.Bob Saget
Active Member
I know this thread is old, but this should be a sticky. This really explains the the conversion differences...I found this thread searching Google. I needed this because the Hana (HI 993301) came stock set a .50 and the Fox Farm feeding schedule, although it also list the EC, uses a .70 conversion.
Now I need to find out if the temperature compensation coefficient needs to be adjusted.
http://www.hannainst.com/images/imgHI_993301_lg.jpg
This might also be helpful.
(EC)——(PPM.5)———(PPM.7)——-(CF)
.4———200————-280———–4
.6———300————-420———–6
.8———400————-560———–8
1.0——–500————-700———-10
1.2——–600————-840———-12
1.4——–700————-980———-14
1.6——–800————-1120———16
1.8——–900————-1260———18
2.0——–1000————1400———20
2.2——–1100————1540———22
2.4——–1200————1680———24
Now I need to find out if the temperature compensation coefficient needs to be adjusted.
http://www.hannainst.com/images/imgHI_993301_lg.jpg
This might also be helpful.
(EC)——(PPM.5)———(PPM.7)——-(CF)
.4———200————-280———–4
.6———300————-420———–6
.8———400————-560———–8
1.0——–500————-700———-10
1.2——–600————-840———-12
1.4——–700————-980———-14
1.6——–800————-1120———16
1.8——–900————-1260———18
2.0——–1000————1400———20
2.2——–1100————1540———22
2.4——–1200————1680———24
RetiredMatthebrute
Well-Known Member
this thread should be a sticky in the hydroponics section. it cleared alot of information up for me as im trying to buy my first all in one meter and thought PPM, TDS and EC were all different measurments but in reality they are all the same measurment.
thanks
thanks
Doer
Well-Known Member
Well, I'm switching to EC thinking, now. The TDS depends on a conversion factor that varies by 20%? I didn't know that, but I see that my software let's me set the conversion in increments of 25 points. What good is that, when we try to communicate?
So, when I see someone saying 0.6 EC, I know what that means. 500 TDS could just as easily be 700 ppm, based on conversion. Weird.
So, when I see someone saying 0.6 EC, I know what that means. 500 TDS could just as easily be 700 ppm, based on conversion. Weird.