pH electrodes

[bromion]

I am considering a DIY temp/pH/other monitoring computer. I was wondering if folks have experience with such things.

Say I want a simple system that will monitor the pH of my tank and store it on a computer. I know commercial devices exist that do that, most requiring proprietary software. Could I do the same thing by:
a) buying a pH sensing electrode (such as the <a href=http://glo.mt.com/mt/products/products-applications_analytical-instruments_lab-electrodes_ph-electrodes_ph-peek-electrodes/InLab413_Combination_pH_Electrode_0x000248ff00025c000002e156.jsp>InLab 413</a>)
b) connecting this to a data acquisition (DAQ) module (USB or PCI, etc)
c) write custom software for the DAQ to interpret the results and store the data.

Does anyone have experience with these probe electrodes? Would they interface simply to a DAQ, or do they require fancy proprietary interfaces sold in the monitors that come with these probes, typically?

Thanks for any info!

 

[slug]

Yes but you need a middle piece. PH electrodes are too low impedence to be read by a dac system, or a cheap voltmeter, so you need to amplify the signal. The device used to do this is usually called a transmitter. Watch ebay for "ph transmitter" for a month or so and you can probably find something under $25.

So you'd have pH probe -> transmitter -> DAC -> computer

 

[perpetual98]

Would a 4-20mV PLC work, or do you still need the transmitter?

 

[ronc98]

Actually PH electrodes are super high impedance. Low output voltage but very high impedance. You can not use common op-amps for this, you need a Jfet or another type of high impedance circuit. You can build one yourself for about 10 dollars in parts.

 

[FuzzyLogic]

<a href=showthread.php?s=&postid=7551431#post7551431 target=_blank>Originally posted</a> by perpetual98
Would a 4-20mV PLC work, or do you still need the transmitter?

You need both if you are doing the PLC thing. You need a PLC that has an analog input and a compatible transmitter. I use a Momentum TSX PLC with 4 analog inputs(4-20mA) and a Rosemount PH analyzer. I found both on eBay for less than $75

 

[slug]

Opps yeah high impedance. I've gotten 3 nice transmiters from ebay, 1 for $10 and 2 for $25 each.

 

[bromion]

Thanks for the info. How long do these probes typically last? Any probe model/manufacturer recommendations?

 

[BeanAnimal]

If you check the national website there is an app note for just such a project.

Bur Brown also makes some nice instrumentation amps that could be easily used with a few external components.... I am sure RONC could add some more details.

 

[slug]

This post has a DIY pH circuit

 

[Gordonious]

Why in the world is this stuff so complicated? I've read a ton of threads about temp and pH probes, why does every single person search for many parts, end up building some of there own, and all end up learning how to program and writing there own program?

Has any one tried using something like:
For pH
http://www.vernier.com/probes/ph-bta.html
For temp
http://www.vernier.com/go/gotemp.html

and using the program logger pro?

This seems as if it would work fine, though later on I would like to have my PC upload or stream the data to my website and I fear there I might have to write my own app unless I can find someone nice enough to share there data.

Does anyone know of some websites where you can see pH and temp of someone's tank online? I have seen one before that had it up the top right of their website, but I forget the exact URL.

Why figure out how to make an airplane fly when it's done by so many people so many times before???

Jon

 

[bromion]

Those look pretty cool. They require you to buy the interface, an extra $220. So if you want to do Ph, Sal, and temp, the total cost is about $450. Cheaper than commercial products for the aquarium.

For complete DIY you need a cheap Ph probe (<a href=http://www.aquabuys.com/page/aqb/PROD/j2/mi_ph_probe>for example</a>) for $40, conductivity probe for salinity ~$50, temp very cheap (or built-in to other probes), plus an inexpensive USB DAQ for $100-150 equals about half the cost. If you have a desktop computer to devote, you could even get away cheaper on the DAQ by buying an old ISA or PCI card. This application doesn't need much in the way of fancy analog I/O. Of course, you need software, which may exist out there for free, or you have to program it yourself. Luckily I know how to program these things already.

It is somewhat annoying this info isn't easily found. I don't mind writing my own programs, but I don't want to buy equipment and find out it doesn't work together!

 

[bromion]

Actually, before I jump into a full DAQ system, I am going to try making a simple temperature monitor/controller with the Go!Temp. Worth a try for $50 and no additional costs, as it's stand-alone.

 

[BeanAnimal]

And you can build an amp and DAC that will hook to the serial or parallel port (or usb even) for $15 or $20 bucks...

The code is rather trivial in most cases....

thats why.

 

[ronc98]

Yes code is always trivial until you spend a year or two on it. I started something like this a few years back and in the end I would have been cheaper to just buy something. If you are doing this for fun that is one thing, if you are doing this to make something cheaper good luck. It will not happen.

 

[BeanAnimal]

Not taling about a whole controller... I was refering to a DIY ph amp DAC and logging program

 

[ronc98]

Sorry BeanAnimal I was not refering to your post. Just some of the upper posts.

These things are fun to do if you have the time, but you certainly will not save money if you are trying to make a whole controller.

It is sometimes worth it though since you can control things the way YOU want to control them.

 

[BeanAnimal]

I do agree My controller is not even up and running... and I have a small fortune in it. We will not even talk about the time and the code

 

[bromion]

A full controller is a tall order. I'm hoping a simple monitoring system will be straightforward and inexpensive to do myself. Maybe I'm foolish, but it'll be fun either way.

 

[Gordonious]

please let me know how things go if you order one of those. I don't want to take any pride in attempting to do something for a year, learning a lot and getting half way there. I wanted to know my ph was horrible and killing my animals three weeks ago. There are a million different ways to buy or build all 8 parts to a DIYS. Why can it not be a simple as one USB probe with a simple app that does nothing but read and store data? I'm hoping this temp prob and pH probe off that site are the answer. The pH probe is about 75, so I guess I'm looking at spending 150. I think I can just use the free software and if not I believe I can get the full program through my school, legally, free.

Jon

 

[Gordonious]

I don't understand why you would buy a probe that you attach to this to attach to that to attach to this to plug into USB for $40 when you can by a probe that plugs into USB for $39. I do get the DIYS part, learning, satisfaction of having done it yourself, but in the end I believe you trust in yourself to not mess up adjust, and tune it all properly and repair any of the many parts when stuff goes wrong. I can't afford even the $39 at this point I'm not spending extra if I do not have to.

I also don't want to leave a computer or any electronic component to adjust the chemistry of my tank, just something to let me know when something needs to be done. I have a FOWLR system with four 20 gallon tanks and 4 fish that could survive living in your beer can, I shouldn't have dramatic changes that need to be adjusted all the time. I can handle once every 4 months having my computer text me and tell me my temp has dropped to a concerning level.