DIY Conductivity Probe/Meter

[porlock]

Of course it is, dooh i'm dump sorry it is late and i drink a couple of beers

 

[tims1000]

the range can be easily adjusted by changing the values of the resistors R16 to R19 but i won't go into that now (unless anyone needs me to)

Hello!

Can u please explain how to adjust range for Your EC meter? Im trying to build it for hydroponic use, so i need range from 0 to some 3000 ppm max, 1500 uS/cm max. Mine probe has constant K=1. Smallest error i could get were around 100 - 200 ppm.

And i couldnt get sine generator to work like in your schematic, without shorting gate with drain.

Thx in advance.

 

[porlock]

tims1000: Bogdan already expanded everything in this topic, please read it all.

 

[bogdanaioane]

Hey Tims1000,

it would be a good idea to go through all that was discussed in this thread as you might find that its best to combine the two designs discussed to achieve best results. this of course depends on what the requirements of your application are.

Just as cliff notes:
if you intend to use this as low conductivity detector (less than 3000ppm) it is best to use the oscillator from my design and the signal amplification from the design that porlock was working on.

I have built this oscillator more than once and without problems (there could still be an error somewhere in the schematic. ill check)
Porlock!..
did you get a chance to build the oscillator from my design? did it work ok for you?

if you read the entire thread and decide to go the route of the Wheatstone Bridge and still need some help understanding the R16-R19 relationship to EC than get back to me and ill be happy to help

Hope this helps

 

[porlock]

Porlock!..
did you get a chance to build the oscillator from my design? did it work ok for you?

Not yet, Christmas time is very busy for me.

 

[porlock]

What trasistor i can use to replace BFT46 ?

 

[xtal]

So if I want to measure 3000 ppm Nacl for my center range .
[ie] 2000 ppm - 4000 ppm which is 4000Us - 8000Us => .004S - .008S
Then @2k with K=1 = 1/(.oo4 *K) = 250 ohm
@3k 1/(.006 *K) = 166.66+ ohm
@4k 1/(.008 *K) = 125 ohm
so what values would I want for R17,R18,R10 , and gain R16

I thinking 150 -180 for R17,18,19 , But ? for R16

 

[martin475]

I worked with the one located here, http://www.octiva.net/projects/ppm/ but it was hard to understand. I tried to reach out to the person, but never heard back from them. I also wanted to include the - 12 VAC conversion in the board so I only needed to suppy 12 VAC instead of + and - 12 VAC.

Unfortunately I do not have a scope.

The probes I purchased from China. The range should work for saltwater, but I will not know until I get a working prototype.

PM me on the PCB if you are interested. I think I have 6 or so extra ones.

 

[martin475]

Just started to read this thread as I am new. its 12vdc into +-12vdc so that the circuit can produce 12vac