pH meter

[George L.]

Hey guys,

Would it be possible to make a electronic pH meter that would have 14 LEDs to indicate the pH of a solution it is placed into.

This would be hard because voltage would change with salinity as well as pH.
Salt in water would have a pH reading, but it is neutral.

Is it possible to make a simple pH meter? Any thoughts?

thanks.

George L.

 

[Papabravo]

I'm assuming here that you cannot directly measure the concentration of H+ ions in solution. Therefore you need to measure some proxy for the actual pH. I'm not sure that there is one, but maybe you can give us a bit of insight here on what we are actually measuring.

Have you considered the corrosive effect of 18M H2SO4 on your probe?

 

[George L.]

The corrosive effect with any acid or base will be noticeable on the probe so it would have to be cleaned. How do the "professional pH sensors" avoid this?

Although I think that a carbon rods (from batteries) will be fairly immune since they don't react with much.

I posted the question because I am expecting it to be more complicated than measuring voltage, I don't know how to go about making something like this.
Basically the more ions, the lower the resistance. That would be the principle.

(No info on the web)

George L.

 

[Hayato]

The corrosive effect with any acid or base will be noticeable on the probe so it would have to be cleaned. How do the "professional pH sensors" avoid this?

Although I think that a carbon rods (from batteries) will be fairly immune since they don't react with much.

I posted the question because I am expecting it to be more complicated than measuring voltage, I don't know how to go about making something like this.
Basically the more ions, the lower the resistance. That would be the principle.

(No info on the web)

George L.

You need to use some precious metal, like platinum.

 

[Roff]

Have you searched for "ph meter theory"? I think you're trying to reinvent the wheel. If there was a simpler solution than the **broken link removed** currently in use, someone would probably have discovered it by now. However, I don't want to discourage you from trying your ideas. Who knows? You might be the one.

 

[mudassir_semiconductor]

yes it is done by efy go for electronics for you mag search u will be getting the data regarding ph .

 

[George L.]

Looking at the "glass cell", it doesn't look like anything a home experimentor could make, I guess I will just have to buy one. Thanks for the link Ron H.

George L.

 

[Roff]

Looking at the "glass cell", it doesn't look like anything a home experimentor could make, I guess I will just have to buy one. Thanks for the link Ron H.

George L.

I think they are available from many sources, but they aren't cheap.

 

[BeeBop]

Would it be possible to make a electronic pH meter that would have 14 LEDs to indicate the pH of a solution it is placed into.

Why not use a single rgb LED which you could drive with PWM? This way it can glow the color related to testing pH with a propanol indicator. (orange= low pH, blue= high pH)

I think they are available from many sources, but they aren't cheap.

Most of the probe makers have a lot of information on measuring pH on their sites. The probes I have bought have all been around $75, and you could spend a lot more. They output a + or - voltage with very high impedance, linear in relation to pH, so you will need to scale it with an op amp.
Some manufactures have come out with probes which need a lot less attention (care and cleaning) but I think the price is quite a bit higher, although I'm not sure about this.

This would be hard because voltage would change with salinity as well as pH.
Salt in water would have a pH reading, but it is neutral.

Yes, the conductivity of the solution will change with the amount of dissolved salts, however you can not measure this by passing a DC current through the solution. It is possible using 1-10 kHz sine wave, and a gold or platinum probe which is in the feedback loop of an op amp.
Salts can exist with varying pH, and the conductivity is also dependent on which salt you are looking at. In other words, you can have a high salt content, and your solution can still be low pH, or high pH.

 

[Hero999]

I've done a quick Google and this place don't seem to be too expensive, a complete mter cost £50, which is no more than a high quality multimeter.

https://www.coleparmer.co.uk/catalog/product_view.asp?sku=5900165
https://www.coleparmer.co.uk/catalog/product_view.asp?sku=3563410&pfx=&lstBool=true

 

[BeeBop]

Yes, the probe is a pretty good deal, with one very good feature:

Applications General purpose; prolonged pH readings

I think this would give long service life without having to do a lot of maintenance.
The problem with the meter is that it only displays a reading on an LCD. If you do it yourself, you have access to the reading which you may log, or use to turn on or off a metering pump. (To control the pH.)

Hanna also makes a pH pen, for even less dollars, but it doesn't look as good as the one in your link.

Something else, is that pH, and conductivity are also temperature dependent. You also need to measure the temperature, and make an adjustment to do it 'right.'

Cole Palmer, is one of those suppliers with a lot of info on their site.

 

[Hero999]

The problem with the meter is that it only displays a reading on an LCD. If you do it yourself, you have access to the reading which you may log, or use to turn on or off a metering pump. (To control the pH.)

You might be able to buy a pH sensor module with in-built drive electronics speciffically designed for industiral control purposes that outputs a voltage (say 0 to 10V) proportional to the pH. I know you can get ultrasonic proximity sensors, temperature sensors and pressure sensors like this so I don't see why you couldn't get a pH sensor.

Something else, is that pH, and conductivity are also temperature dependent. You also need to measure the temperature, and make an adjustment to do it 'right.'

I haven't checked but I'd assume that the commercial pH meters have built-in temperature compensation.

 

[Hero999]

I've done a quick Google for you

**broken link removed**
https://glo.mt.com/mt/filters/produ..._family_browsw_0x000249740002871b0003f47b.jsp

No prices are shown but they do look expensive.

 

[BeeBop]

Yes, of course, Hero. Your first link, I think it was, was to a 'sensor,' or probe. I thought it was a pretty good deal, too.

You might be able to buy a pH sensor module with in-built drive electronics speciffically designed for industiral control purposes that outputs a voltage (say 0 to 10V) proportional to the pH.

Yes, and they tend to be quite expensive, which is why it is so much more fun to build yourself!

Also, building your own circuit is some good time working with op amps, which can be as intriguing as microcontrollers are. As well as using an op amp to scale your pH, it is also an opportunity to get some experience with an NTC thermistor, and how to linearize, and scale that.

I haven't checked but I'd assume that the commercial pH meters have built-in temperature compensation.

Yes, I think you are right on this one. But like I say, it is a great project, really worth doing.

He, he, this always scares me:

No prices are shown but they do look expensive.

I think the ones I got were pretty good, but then I'm no expert. One of them was made in Canada, and they are both on the way to Canada, along with most of my toys. I'll sure miss being here, where one can go shopping in 'electronics dreamland,' and find many exciting things. (Not to mention the fun of dealing on them, in a language I'm not good at.)