Go Down

### Topic: Conductivity measuring  (Read 3305 times)previous topic - next topic

#### Dragonsired1

##### Sep 10, 2017, 06:52 pmLast Edit: Sep 10, 2017, 07:51 pm by Dragonsired1
Hello,

I tried to find an easy and reliable way of measuring conductivity of water samples but failed by looking on very complicated schematics. I don't want to use voltage divider as it makes more problems than usefull data. Please can you provide me with more information about this topic?

Thanks.

#### Paul_KD7HB

#1
##### Sep 11, 2017, 04:23 am
Hello,

I tried to find an easy and reliable way of measuring conductivity of water samples but failed by looking on very complicated schematics. I don't want to use voltage divider as it makes more problems than usefull data. Please can you provide me with more information about this topic?

Thanks.
Conductivity is the reciprocal or resistivity.

Out old circuit board washer measured the resistivity of the water and stopped washing at 1 meg ohm. The new board washer stops washing when the wash water measures 1 microSiemen. Same exact measurement, just different values.

What is your problem with voltage dividers? Somewhere you have to have a range of voltages that an Arduino can measure.

Paul

#### Dragonsired1

#2
##### Sep 11, 2017, 10:02 amLast Edit: Sep 11, 2017, 10:39 am by Dragonsired1
Quote
What is your problem with voltage dividers?
The problem is, that there's too much voltage across probe and electrolysis occurs. First two readings are OK but after some time results vary more than 100%. I found somewhat easy solution with 555 here:
555-conductivity-meter
But the problem is that Arduino would have to then measure frequency which is tricky.
I though about using frequency to voltage circuit or try to make steady current source for let say 25uA and use simple ohms law to calculate voltage with given resistance. What's better idea?

#### stowite

#3
##### Sep 12, 2017, 10:27 am
But the problem is that Arduino would have to then measure frequency which is tricky.
To my mind just the opposite of tricky. There are many many examples of using Arduino to measure frequency.

#### Wawa

#4
##### Sep 14, 2017, 04:09 am
There have been TDS (total dissolved solids) threads on this site.
This one (post#40) might start you off.
Leo..

#### Delta_G

#5
##### Sep 14, 2017, 05:45 am
The problem is, that there's too much voltage across probe and electrolysis occurs.
Yeah, don't use DC.
|| | ||| | || | ||  ~Woodstock

Please do not PM with technical questions or comments.  Keep Arduino stuff out on the boards where it belongs.

#### Johan_Ha

#6
##### Sep 17, 2017, 07:37 am
Quote
The problem is, that there's too much voltage across probe and electrolysis occurs.
Even if the voltage is there only for a millisecond?
____________________

If you ask for help and write 'u' instead of 'you' because you think it's convenient, I will write 'no' instead of 'yes'. For same reasons.

#### Dragonsired1

#7
##### Nov 19, 2017, 01:01 am
There have been TDS (total dissolved solids) threads on this site.
This one (post#40) might start you off.
Leo..
That sounds promising! A was doing some research and made that 555timer conductivity circuit. Well it works sort of but DC voltage is still problem. I'm using in my project old PC power supply which has 5+V and 5-V can I make use of it?? I was even thinking about H-bridge and inverters to convert DC to AC. What's the best idea for that?

#### Wawa

#8
##### Nov 19, 2017, 01:37 am
That sounds promising! A was doing some research and made that 555timer conductivity circuit. Well it works sort of but DC voltage is still problem. I'm using in my project old PC power supply which has 5+V and 5-V can I make use of it?? I was even thinking about H-bridge and inverters to convert DC to AC. What's the best idea for that?
If you feed a square wave with DC component (e.g. 0/5volt) through a (DC blocking) capacitor, then you have a pure AC square wave (+2.5volt/-2.5volt) on the other side.
No need to use a dual rail supply.
Leo..

#### jremington

#9
##### Nov 19, 2017, 02:43 amLast Edit: Nov 19, 2017, 02:45 am by jremington
Another DIY TDS meter, with AC probe, but all analog circuitry.

Go Up