Found this topic from a Google search and thought I'd revive the thread as I'm in the process of building a similar automated system. I'm wondering about the status of this project, and about the probes. I also thought I would add for comment that I've seen elsewhere the use of titanium for the probes. Any thoughts on that?
DIY Conductivity Probe/Meter
- Thread starter cyrusthevirus
- Start date
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We're working on a portable water purifier with a built in tester and one of the parameter that our tester should be able to measure is the salinity of water... can you share to us the current status of your circuit? if you could share to us sir... we're also trying to build a ORP tester if there is anything you could share to us we would be very thankful.... poviclang@yahoo.com
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We're working on a portable water purifier with a built in tester and one of the parameter that our tester should be able to measure is the salinity of water... can you share to us the current status of your circuit? if you could share to us sir... we're also trying to build a ORP tester if there is anything you could share to us we would be very thankful.... poviclang@yahoo.com
Last edited:
cyrusthevirus
New member
Every couple of years I get some interest in this circuit so I wanted to provide the current status. Unfortunately the status has not changed. I have EC probes but I am not sure if they will work for the range required. If anyone wants to try to take this project on, PM me. I can send over the prototypes I created. I just don't have the equipment or the time.
Hi
I am designing a conductivity probe which consists of coaxial cylindrical electrodes in order to measure the electrical conductivity of electrolyte solutions. I can't seem to find any literature on how to go about the design and how these type of sensors work. Do you guys recommend any textbooks or literature that explains this really well as I don't have an electrical background.
Many Thanks
I am designing a conductivity probe which consists of coaxial cylindrical electrodes in order to measure the electrical conductivity of electrolyte solutions. I can't seem to find any literature on how to go about the design and how these type of sensors work. Do you guys recommend any textbooks or literature that explains this really well as I don't have an electrical background.
Many Thanks
surajpadhy
New member
TDS Schematic
TDS Schematic
I used the schematic available at octiva.com but it didn't worked for me. there was no change at output when the water or a connected resistance value was changed.
Please suggest any corrections in that schematic or any other working circuit.
Thanks..
TDS Schematic
I used the schematic available at octiva.com but it didn't worked for me. there was no change at output when the water or a connected resistance value was changed.
Please suggest any corrections in that schematic or any other working circuit.
Thanks..
fustilarian
New member
Just skimmed this thread and saw no mention of this company so i figured i'd chime in with it. www.atlas-scientific.com sells all sorts of useful diy probes and circuit boards to read the probes and output i2c or UART. Not exactly cyrusthevirus level DIY but for all the wannabe EE's out there (like me) it should suffice. HTH
Sorry for the delay, I was out of town. Here is the diagram for my circuit. It should work. I have had it reviewed by a lot of people. PM me if you are interested, I have some extra PCBs of it.
On another note I received all of my probes. I need to setup my standardized solutions so I can begin testing.
Could you share the pcb layout ?
pringlescan
New member
Off the shelf circuit available & Potential Pitfalls
Off the shelf circuit available & Potential Pitfalls
Hello All,
I was wondering on how you were making out with your DIY circuit. I was unable to find a completely implemented and tested EC probe and circuit in the Arduino community so I opted to go with this:
The Atlas Scientific stuff is expensive but easy to interface with and accurate. It expects you to know your probes cell constant (K) value. This is apparently related to the distance between conductors and the surface area exposed. I have yet to see a cheap probe specify this value. I have reached out to several vendors and am awaiting a response.
I have both 111800us/cm and 12880us/cm conductivity solution to perform a two-point (high/low) calibration. After calibration, I get the correct EC values for both solutions despite them being well outside the specifications of my probe.
The problem I ran into however was that the specific gravity does not match my refractometer even when the EC value is accurate.
This is my refractometer, I have calibrated it using distilled water according to the manufacturers instructions:
http://www.amazon.com/Refractometer...&qid=1420305030&sr=8-1&keywords=refractometer
I was under the assumption that using the EC value you could derive the specific gravity, salinity, and TDS.
Apparently, it may not be that simple. As even with the correct EC value, you can still have an incorrect specific gravity/salinity with this commercial/scientific/well-tested circuit.
I'm posting here because I'm interested in not using a $50 circuit in my open source aquarium project... and also because I have yet to get this to work correctly.
I also want to caution interested parties that this in theory is trivial, but in practice can be complicated. Lights and pumps are notorious for leaking electrical noise (and with faulty equipment current!). Sharing a common ground between your aquarium equipment and your microcontroller can skew results.
It's also worth noting that you'll need to have your EC probe off for a second or two before your PH probe (and possibly other probes) take measurements.
Off the shelf circuit available & Potential Pitfalls
Hello All,
I was wondering on how you were making out with your DIY circuit. I was unable to find a completely implemented and tested EC probe and circuit in the Arduino community so I opted to go with this:
- http://www.atlas-scientific.com/product_pages/circuits/ezo_ec.html
- http://www.aliexpress.com/snapshot/6366159184.html?orderId=64777608620548
The Atlas Scientific stuff is expensive but easy to interface with and accurate. It expects you to know your probes cell constant (K) value. This is apparently related to the distance between conductors and the surface area exposed. I have yet to see a cheap probe specify this value. I have reached out to several vendors and am awaiting a response.
I have both 111800us/cm and 12880us/cm conductivity solution to perform a two-point (high/low) calibration. After calibration, I get the correct EC values for both solutions despite them being well outside the specifications of my probe.
The problem I ran into however was that the specific gravity does not match my refractometer even when the EC value is accurate.
This is my refractometer, I have calibrated it using distilled water according to the manufacturers instructions:
http://www.amazon.com/Refractometer...&qid=1420305030&sr=8-1&keywords=refractometer
I was under the assumption that using the EC value you could derive the specific gravity, salinity, and TDS.
Apparently, it may not be that simple. As even with the correct EC value, you can still have an incorrect specific gravity/salinity with this commercial/scientific/well-tested circuit.
I'm posting here because I'm interested in not using a $50 circuit in my open source aquarium project... and also because I have yet to get this to work correctly.
I also want to caution interested parties that this in theory is trivial, but in practice can be complicated. Lights and pumps are notorious for leaking electrical noise (and with faulty equipment current!). Sharing a common ground between your aquarium equipment and your microcontroller can skew results.
It's also worth noting that you'll need to have your EC probe off for a second or two before your PH probe (and possibly other probes) take measurements.
BeanAnimal
Premium Member
I am not quite sure I would agree regarding the quality if the Atlas Scientific stuff...
At one point they claimed that their PH circuit did not need calibration... uhh yeah, sure if you use their PH probe and assume that they are all pre-tested to fit the hard coded slope, sensitivity and offset in the circuit... nonsense. I purchased one for giggles and find it to be useless.
Anyway...
At one point they claimed that their PH circuit did not need calibration... uhh yeah, sure if you use their PH probe and assume that they are all pre-tested to fit the hard coded slope, sensitivity and offset in the circuit... nonsense. I purchased one for giggles and find it to be useless.
Anyway...
Ugh, I just order the Atlas EC kit a few days ago. It is certainly not cheap, I just hope it works as expected.
I already have their ORP and Oxygen. The Oxygen has worked fine, buy the ORP has been very sensitive to other electrical interference. I attribute it to the EMI thrown off by my PWM lines driving my Meanwell boards. The readings would become crazy as soon as my LEDs would kick on for the day. To help counter this I changed my PWM lines to using shielded CAT-5 for the longish run to the lights. This helped somewhat. My Oxygen probe became useable, the ORP not so much. So for this order I added one of their carrier boards so that I can try to isolate the probe circuits into a remote shielded box near the tank.
The Atlas Scientific stuff appears to be very sensitive. Hopefully the ground plane on the carrier is able to alleviate some of the tendency to be unstable.
Dennis
I already have their ORP and Oxygen. The Oxygen has worked fine, buy the ORP has been very sensitive to other electrical interference. I attribute it to the EMI thrown off by my PWM lines driving my Meanwell boards. The readings would become crazy as soon as my LEDs would kick on for the day. To help counter this I changed my PWM lines to using shielded CAT-5 for the longish run to the lights. This helped somewhat. My Oxygen probe became useable, the ORP not so much. So for this order I added one of their carrier boards so that I can try to isolate the probe circuits into a remote shielded box near the tank.
The Atlas Scientific stuff appears to be very sensitive. Hopefully the ground plane on the carrier is able to alleviate some of the tendency to be unstable.
Dennis
Has anybody considered the pulse count method, I've seen a couple of 555 timer chips with probe attached, the count represents the salinity level..
I'm wanting to measure my pool water, salt ppm[4000-6000uS/cm] , and ph,Temp and transmit over 1-wire
Did find that somebody recommended titanium wire [ available from McMaster] for probe
also found 3 conversion factors
EC * 500 [USA] = ppm
EC * 640 [EU] = ppm
EC * 700 [AU] = ppm
my biggest problem is creating satisfactory calibration solution 2000 ppm, 3000 ppm
did breadboard a 555 seemed to work but was temperature sensitive.
I'm wanting to measure my pool water, salt ppm[4000-6000uS/cm] , and ph,Temp and transmit over 1-wire
Did find that somebody recommended titanium wire [ available from McMaster] for probe
also found 3 conversion factors
EC * 500 [USA] = ppm
EC * 640 [EU] = ppm
EC * 700 [AU] = ppm
my biggest problem is creating satisfactory calibration solution 2000 ppm, 3000 ppm
did breadboard a 555 seemed to work but was temperature sensitive.
pringlescan
New member
Why does it differ by country?
I ordered a jewelers scale and some lab implements I plan to make my own solutions. I haven't figured out how I want to do it yet, but that seemed like the bare minimum I'd need for precise measurements. EC test solutions are expensive and way outside the range most are testing for. I think 50,000 us/cm is equivalent to seawater. I was unable to find any solutions close to that.
I ordered a jewelers scale and some lab implements I plan to make my own solutions. I haven't figured out how I want to do it yet, but that seemed like the bare minimum I'd need for precise measurements. EC test solutions are expensive and way outside the range most are testing for. I think 50,000 us/cm is equivalent to seawater. I was unable to find any solutions close to that.
I would suspect the reason for the difference in the conversions would be they're different chemicals for their standard [just guessing]...
If my thinking is correct 6000 us = 6 mS/cm * 500 =3000 ppm
also 6mS/cm = .006 S/cm => mho Therefore
R = 166 ohms
R@.004 =250 ohm
R@.005 =200 ohm
R@.007 = 142 ohm
So I would want a probe to be reliable from 4000us-7000us, 142-250 ohms.
I think a K =1 , but not sure mechanical demensions
I did see a description of 2 1cmx1cm plates separated by 1cm , but not sure if I under stood this correctly...
If my thinking is correct 6000 us = 6 mS/cm * 500 =3000 ppm
also 6mS/cm = .006 S/cm => mho Therefore
R = 166 ohms
R@.004 =250 ohm
R@.005 =200 ohm
R@.007 = 142 ohm
So I would want a probe to be reliable from 4000us-7000us, 142-250 ohms.
I think a K =1 , but not sure mechanical demensions
I did see a description of 2 1cmx1cm plates separated by 1cm , but not sure if I under stood this correctly...
TDS meter etc
TDS meter etc
Have completed a pulse counting TDS meter, my problem now is I need several good calibration solutions, and a good k 1.0 probe..
The pulse circuit is LM555 timer timer chip [ similiar to atlas scientific] which feeds a 16f1825 pic running 32mhz... The 555 circuit itself appears to be temperature sensitive. And requires more investigation. I have attached the source code -in proton basic and a hex file..
In case anyone is interested...
It captures pulses for 32000 us into T1 ctr, I have captured 64000 counts reliably. I take 8 samples of the pulses and also of the temperature [DS18b20]
I have 5 Probe tables that will hold 10 calibration ppm/count values each
you have to manually add the values with a command [ RS232 ] other command are available - see source code
I have some test code using port c to derive Bipolar signal from op amp
-was trying to play with pulse TDS measurement
My current timer is using a .022uf cap and with 150 ohm {probe-resistor}
I get approx 44000 pulses, If I place my finger on the 555 chip the pulse rate slowly drops to 43000+ [ ie temp sensitive]
If I can come up with a good probe and embed the DS18b20 I think it will be a viable design:wavehand:
TDS meter etc
Have completed a pulse counting TDS meter, my problem now is I need several good calibration solutions, and a good k 1.0 probe..
The pulse circuit is LM555 timer timer chip [ similiar to atlas scientific] which feeds a 16f1825 pic running 32mhz... The 555 circuit itself appears to be temperature sensitive. And requires more investigation. I have attached the source code -in proton basic and a hex file..
In case anyone is interested...
It captures pulses for 32000 us into T1 ctr, I have captured 64000 counts reliably. I take 8 samples of the pulses and also of the temperature [DS18b20]
I have 5 Probe tables that will hold 10 calibration ppm/count values each
you have to manually add the values with a command [ RS232 ] other command are available - see source code
I have some test code using port c to derive Bipolar signal from op amp
-was trying to play with pulse TDS measurement
My current timer is using a .022uf cap and with 150 ohm {probe-resistor}
I get approx 44000 pulses, If I place my finger on the 555 chip the pulse rate slowly drops to 43000+ [ ie temp sensitive]
If I can come up with a good probe and embed the DS18b20 I think it will be a viable design:wavehand:
Just to follow up on my post above about the Atlas Scientific EC probe. Another failure, I was not able to get it to be reliable. It would drift out of calibration over a matter of days. I never figured out what the issue was. At first I thought my grounding probe may have been the cause, but that was short lived.
Of the 3 kits I ordered (ORP,EC, DO), I was only ever able to get the Dissolved Oxygen one working reliably. Some people report good results with their stuff, but that has not been my experience.
Dennis
Tds
Tds
I miss quoted about the atlas-scientific I not sure what method they use...
It is the OWL2C by EME Systems thats using lmc555 mounted on about 1" x 1"
pca ....The main problem I'm seeing with my setup is the temperature drift of the circuit ...
I was thinking about investing in the Atlas Scientific, but no so sure now,
did you also get their probe @ what K value...
I'm thinking I could compute K by measuring the EC in a calibration solution
Then use a resistor to obtain the same EC then
compute conductance * K = conductivity
K / R = conductivity
K = conductivity * R
If my math and thinking is correct
Tds
I miss quoted about the atlas-scientific I not sure what method they use...
It is the OWL2C by EME Systems thats using lmc555 mounted on about 1" x 1"
pca ....The main problem I'm seeing with my setup is the temperature drift of the circuit ...
I was thinking about investing in the Atlas Scientific, but no so sure now,
did you also get their probe @ what K value...
I'm thinking I could compute K by measuring the EC in a calibration solution
Then use a resistor to obtain the same EC then
compute conductance * K = conductivity
K / R = conductivity
K = conductivity * R
If my math and thinking is correct
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bogdanaioane
New member
EC Meter
EC Meter
Hello All
This is my first time posting on one of these forums so please forgive me if I go wrong.
I have been reading this post and I feel I should contribute with some of my knowledge and understanding on this. I started developing an aquarium control system two years ago and am still in the said process. However I have finished the design and initial tests on the EC Module and am quite happy with the results.
If people are still interested in developing their own EC controller please write in this post and ill be sure to post schematics and more detail instructions on how to build one.
This thing that I'm making will be a commercial system but will most importantly be open source for people to make their own if they want to or feel it would be cheaper that way. So I figure what better place to start to release these plans and instructions freely than on forums such as these with people that are eager to make something out of nothing.
So... EC Meter
In this post I will cover the concepts involved in measuring EC of salt water.
1. Probe
An EC probe doesn't really have a range in the normal sense (like say a PH probe would have a range) it has a cell constant K which is the distance between the two electrodes divided by the contact area of the electrodes (so two plates of 1cm square each placed at 1cm from one another would give you a constant K=1) Its what circuitry you design and build that together with a probe of a certain constant would enable you to measure a specific range. So to answer one user that wasn't sure if a K=10 probe would be ok for 53000us, yes it would provided you take into account what I am mentioning above.
2.Signal
The voltage applied tot the electrodes HAS to be AC. And this doesn't mean that it has to be a sinewave really it could be square wave or any other shape of wave as long as its balanced equally with respect to GND. The frequency of this "pulse" has to be higher than 3Khz (some literature suggests even higher) The reason for the AC condition is that you need to prevent the positive charged ions from migrating and attaching to the negative electrode and the negative charged ions .... to the positive electrode (we don't want electrolysis). A good solution for generating a stable sinewave for this purpose is a oscillator with automatic gain control using an op amp (I will add schematic in my next post)
this signal has to be stable and unaffected by supply voltage fluctuations.
3.Amplification
Once you generate the signal you then pass this through an op amp to get an amplified signal at the other end. In this amplification stage, you replace the resistor that sets the gain with your probe. And that's about it really. In the circuit I designed I used an instrumentation amplifier that improves linearity. And the probe is actually part of something called a Wheatstone Bridge.(schematic to follow)
4. Signal Rectification
Once we amplified the signal, we still need to rectify it to be able to supply it into a measuring MCU or arduino or similar and since we have only used one of the two stages of a typical op amp in signal generation, we will use the other one together with two diodes to rectify the signal. THE END
One important aspect that I haven't seen discussed on this or any other forum for that matter is galvanic insulation (this thing or better yet the lack of, can make for pretty erroneous readings due to stray voltages and ground loops, especially in measurements like EC where your electrodes are in direct contact with the water) Just a thought.
I hope this hasn't been too much words and not enough substance and please feel free to correct me if I'm wrong and post your comments and if interested let me know and I will add some pictures and schematics to this for you.
EC Meter
Hello All
This is my first time posting on one of these forums so please forgive me if I go wrong.
I have been reading this post and I feel I should contribute with some of my knowledge and understanding on this. I started developing an aquarium control system two years ago and am still in the said process. However I have finished the design and initial tests on the EC Module and am quite happy with the results.
If people are still interested in developing their own EC controller please write in this post and ill be sure to post schematics and more detail instructions on how to build one.
This thing that I'm making will be a commercial system but will most importantly be open source for people to make their own if they want to or feel it would be cheaper that way. So I figure what better place to start to release these plans and instructions freely than on forums such as these with people that are eager to make something out of nothing.
So... EC Meter
In this post I will cover the concepts involved in measuring EC of salt water.
1. Probe
An EC probe doesn't really have a range in the normal sense (like say a PH probe would have a range) it has a cell constant K which is the distance between the two electrodes divided by the contact area of the electrodes (so two plates of 1cm square each placed at 1cm from one another would give you a constant K=1) Its what circuitry you design and build that together with a probe of a certain constant would enable you to measure a specific range. So to answer one user that wasn't sure if a K=10 probe would be ok for 53000us, yes it would provided you take into account what I am mentioning above.
2.Signal
The voltage applied tot the electrodes HAS to be AC. And this doesn't mean that it has to be a sinewave really it could be square wave or any other shape of wave as long as its balanced equally with respect to GND. The frequency of this "pulse" has to be higher than 3Khz (some literature suggests even higher) The reason for the AC condition is that you need to prevent the positive charged ions from migrating and attaching to the negative electrode and the negative charged ions .... to the positive electrode (we don't want electrolysis). A good solution for generating a stable sinewave for this purpose is a oscillator with automatic gain control using an op amp (I will add schematic in my next post)
this signal has to be stable and unaffected by supply voltage fluctuations.
3.Amplification
Once you generate the signal you then pass this through an op amp to get an amplified signal at the other end. In this amplification stage, you replace the resistor that sets the gain with your probe. And that's about it really. In the circuit I designed I used an instrumentation amplifier that improves linearity. And the probe is actually part of something called a Wheatstone Bridge.(schematic to follow)
4. Signal Rectification
Once we amplified the signal, we still need to rectify it to be able to supply it into a measuring MCU or arduino or similar and since we have only used one of the two stages of a typical op amp in signal generation, we will use the other one together with two diodes to rectify the signal. THE END
One important aspect that I haven't seen discussed on this or any other forum for that matter is galvanic insulation (this thing or better yet the lack of, can make for pretty erroneous readings due to stray voltages and ground loops, especially in measurements like EC where your electrodes are in direct contact with the water) Just a thought.
I hope this hasn't been too much words and not enough substance and please feel free to correct me if I'm wrong and post your comments and if interested let me know and I will add some pictures and schematics to this for you.
geekengineer
Member
So what is the point of measuring EC for saltwater? is there some assumption it would correlate with specific gravity? I didn't think that totally worked? I think in order to measure EC automagically for a fluid you need something mechanical in nature or a load cell device.
bogdanaioane
New member
yes something like that
refractive index, specific gravity, and electrical conductivity are all indirect methods of determining the salinity of water which is what we actually need to control. in alot of cases there is no direct relation between these 3 indirect measurement methods and salinity but in the case of sea water there is. out of the 3 methods EC has the potential of being the most accurate and stable followed by refractive index and then specific gravity. I once tried using a load cell from a precission jewlery scale to make a specific gravity sensor and i can say that it works but is nowhere near the stability and accuracy of a well designed and built EC meter.
Hope this helps
refractive index, specific gravity, and electrical conductivity are all indirect methods of determining the salinity of water which is what we actually need to control. in alot of cases there is no direct relation between these 3 indirect measurement methods and salinity but in the case of sea water there is. out of the 3 methods EC has the potential of being the most accurate and stable followed by refractive index and then specific gravity. I once tried using a load cell from a precission jewlery scale to make a specific gravity sensor and i can say that it works but is nowhere near the stability and accuracy of a well designed and built EC meter.
Hope this helps
geekengineer
Member
ah ok.. I did mean to say "I think in order to measure SG automagically for a fluid" not EC.. looks like you got it.
So you can use it just not direct correlation but more stable measurement ok. I think I understand. If you make a probe yourself I believe you will need some platinum wire for the electrodes so they don't corrode out.
So you can use it just not direct correlation but more stable measurement ok. I think I understand. If you make a probe yourself I believe you will need some platinum wire for the electrodes so they don't corrode out.
