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ph meter

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neelam29

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hi all,
m designing a ph meter using ca3140 for the first stage where we in m directly connecting the probe of the ph electrode to pin 3 of the opamp and thru pin 2 feedback is attached... and also tried attaching 100k & 10M resistance in between pin 3 and electrode... but since the impedance of the probe is high m not getting proper results...what should i do? please help me out
 
You may already know this, but I was told for glass pH probes that leakage current is an issue in the circuit itself and the pcb's generally must be made. Look into "guard conductors" for information on how leakage current is controlled. Here is a link to a op-amp datasheet that covers some of this information and also has a pH probe circuit as one of its typical applications.

**broken link removed**

I'm not sure this is your problem, but I hope it helps.

James
 
3140s run about 10^10th at the input. A more modern op amp with a higher input resistance would be better. Ypu might like an OPA127 - 10^13th and only 5 pa leakage.
 
Icl7621

Hi,

I am also building a pH-circuit and I use the ICL7621 chip. It works fine for me....:)

Kind regards,
Jack
 

Attachments

  • pH-ICL7621.jpg
    pH-ICL7621.jpg
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JackE said:
Hi,

I am also building a pH-circuit and I use the ICL7621 chip. It works fine for me....:)

Kind regards,
Jack

Too bad your schematic is too small to see it clearly!
 
chemelec said:
Too bad your schematic is too small to see it clearly!
It is too bad the schematic has those awful grid lines and was saved as a fuzzy JPG file type instead of a very clear GIF or PNG file type.
 
pH amplifier

chemelec said:
Too bad your schematic is too small to see it clearly!

Hi,

Hope it's better......;)
Although not very sharp, one can see the application of the ICL7621.....
This is a combined pH/ORP amplifier.


Kind regards,
Jack.
 

Attachments

  • ph_amp.gif
    ph_amp.gif
    65.2 KB · Views: 2,789
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JackE said:
Hi,

Hope it's better......;)
Although not very sharp, one can see the application of the ICL7621.....
This is a combined pH/ORP amplifier.


Kind regards,
Jack.

Much Better.

Curious, do you have a link for the origional article?

Also What is "ORP"?
 
Someday I would like to build networked pH meters for my ponds. It does not have to be bang on just good enough to tell when things are changing. When ponds go bad they move from 7 or 8 to pH 6 or less.

What sort of probe are you using?
Does anyone know where to get or how to build inexpensive ones?

So far all the ones I have seen on the net are out of my price range.
 
low cost pH meter amplifier

3v0 said:
Someday I would like to build networked pH meters for my ponds. It does not have to be bang on just good enough to tell when things are changing. When ponds go bad they move from 7 or 8 to pH 6 or less.

What sort of probe are you using?
Does anyone know where to get or how to build inexpensive ones?

So far all the ones I have seen on the net are out of my price range.

Hi,

I am building a low-cost pH / ORP (oxidation-reduction potential = redox) system. Multiple sensors will be connected, each sensor having its own potential seperated amplifier using a DC-DC convertor to drive the circuit. The analogue value will then be translated into a digital value by a low cost PIC processor (PIC12F675). On command of a host (PC or any intelligent controller) a master controller will read out all the values from the sensor-circuits and transport them to the host. Reading out the sensor-circuit will occur with opto-couplers to assure galvanic seperation of all the circuits. This way I will be able to read multiple sensors used in my reef tank without interfering each other.

I am still looking for a pH probe but think of using a HANNA probe: HI-1332/B.....Hanna also have ORP probes which are very usable.....Also Milwaukee has some usable pH probes (e.g. MA911)

The PIC controller in the circuit will also be used for software calibration purposes. This gives me the most design flexibility....:)

Overall, the circuit is low cost as the main components just cost a few euros (1 euro = 1.30 US$ at this time). The PCB will be the most expensive part though.....:rolleyes:

Kind regards,
Jack.
 
chemelec said:
Much Better.

Curious, do you have a link for the origional article?

Also What is "ORP"?


Hi,

The design is still a draft.....
(ORP = oxidation-reduction potential = redox)

Kind regards,
Jack.
 

Attachments

  • pH_Amplifier.pdf
    32.4 KB · Views: 1,449
Keep us posted regarding probes esp if you can find ones at a reasonable price. I would need several and at about $40 a pop it would add up. I seen some less expenisve ones using a cloth junction for $18 but I have doubts about that.

Look for a PM from me regarding boards.
 
"Real men write machine code by hand and load it in with toggle switches"- For a better experience, sit on a tall stool and punch the code into the register with the indicator/switches, and manually toggle it into core memory.
 
j.p.bill said:
"Real men write machine code by hand and load it in with toggle switches"- For a better experience, sit on a tall stool and punch the code into the register with the indicator/switches, and manually toggle it into core memory.

Perhaps
"Real men write machine code by hand and manually toggle it into core memory with the front panel"
 
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