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Taking automatic readings using computers and sensors
http://byap.backyardmagazines.com/forum/viewtopic.php?f=1&t=838		 Page 1 of 2
Author:  MCPHRO [ Nov 22nd, '06, 16:51 ]
Post subject:  Taking automatic readings using computers and sensors
We were thinking as part of a discussion today of using a computer to take automatic readings of the different elements of an aquaponic system. It was seen on New Inventors show on a laptop as they conducted the interview.

1. Has anyone tried this?
2. Does anyone know much about doing this.
3. Does anyone know of any software around that does this, freeware or otherwise.

We are going to a reef guardian environment day next week, ill be asking the questions there and ill report back here what i find out
Author:  b2barker [ Nov 23rd, '06, 08:02 ]
Post subject:  Re: Taking automatic readings using computers and sensors
Myself, Royale and Steve have some experience in the process control industry. There are some threads on using PLCs/smart relays for automation. It is the hardware more than the software that will cost to do this. A PLC with 6-8 inputs (a couple configurable for analogs) and 6 outputs is about $200, but the instruments to measure a level, ph, temp, or whatever will also cost.
For pure data acquisition I think the Labjack is pretty cost effective. This and others like it are available from Ocean Controls or Turnkey Solutions.
Hope that helps
Author:  steve [ Nov 23rd, '06, 17:55 ]
Post subject: 
I'm getting lazy, i was hoping one of you teckies would post the long answer :) Thanks!

Just bear in mind that the data aq. card will probably want a 0 to 10V (or simmilar) input, most hand held PH, and DO meters at best have an rs232 output. I don't think is possible to D aq. those two CHEAPLY.
Author:  bundaberg kid [ Nov 23rd, '06, 18:21 ]
Post subject: 
I used to work at a poo farm that was 95% automated....sending the data to the pc/ control system is easy and relativley cheap via rs232 or a 4-20mA current loop....BUT your instrumentation wont be cheap. For a small system I reckon it would be a waste of time..unless you got lots of dough, then play away.

The benefits of using instrumentation for analysis of your system would be educational but would is more beneficial on a much larger scale, by this I mean time saving....cost saving( less employee's for system monitoring/control) and partial/full system automation.

The fun at an educational level would be a more hands on approach..... using the test kits and making a chart to record your findings, drawing graphs and comparing stock levels to the water test results etc.....but thats just me ramblin...or is it the rum lol
Author:  MCPHRO [ Nov 24th, '06, 05:14 ]
Post subject:  Re: Taking automatic readings using computers and sensors
nah, wed prefer to take the data by hand. But It would be great to have it also animated so the kids could compair their data, with the real one. Also, the kids would only get to take the data every few days, it depends when they have class. You could then discuss why the need for regular and sampling often is mroe acurate simply because you are sampling more often. Also, a computer sampled system would save money on test kits in the long run...


But we want instead to do it by hand...
Author:  James Newton [ Nov 24th, '06, 13:50 ]
Post subject:  Re: Taking automatic readings using computers and sensors
Ph and temp are pretty cheap to log, e.g. that LabJack system, and I have seen low cost systems for measuring desolved CO2, but dissolved O2 seems to be the really expensive one. $199 is the best price I've seen for a DO sensor. That was from http://www.vernier.com. Anyone seen a cheaper DO probe? Or know a way of inferring it from other measurements?
Author:  bundaberg kid [ Nov 24th, '06, 19:27 ]
Post subject:  Re: Taking automatic readings using computers and sensors
MCPHRO wrote:
nah, wed prefer to take the data by hand. But It would be great to have it also animated so the kids could compair their data, with the real one. Also, the kids would only get to take the data every few days, it depends when they have class. You could then discuss why the need for regular and sampling often is mroe acurate simply because you are sampling more often. Also, a computer sampled system would save money on test kits in the long run...


But we want instead to do it by hand...



It might save you money in the long run, but I would look into the ongoing expenses for the test gear/instrumentation you might want to use.

This might include replacement sensors due to their possible limited life spans and calibration standards for your ongoing routine maintenance...you might find that the ongoing costs of the upkeep of your sampling gear outweighing the cost of a basic test kit...but this all depends on what your going to be sampling/recording on the pc.

Just something else to keep in mind :D
Author:  steve [ Nov 24th, '06, 19:31 ]
Post subject: 
Also be away that only the high end process control Ph and DO probes are rated at continuous (line mount) usage.
Author:  Doug_Basberg [ Dec 2nd, '06, 10:14 ]
Post subject: 
Steve has pointed out the worst problem with DO probes.

I would pay $200 for a probe that can stay in the tank. But the $200 probe is for a quick dip reading and then a wipe down.

If you want to take hourly DO readings on the computer, you need a tank mounted probe. What is the cheapest full time DO probe?

I have seen a $500 probe. Anyone seen one cheaper?
Author:  dthawk [ Dec 2nd, '06, 12:31 ]
Post subject: 
nope....
Author:  steve [ Dec 2nd, '06, 13:32 ]
Post subject: 
sorry.
Author:  njh [ Dec 22nd, '06, 12:19 ]
Post subject: 
You can buy oxygen permeable membranes fairly easily, I wonder if you could make a gauge using an evacuated tube with a pressure sensor inside. The dissolved O2 will find an equilibrium with the vacuum and that produce a pressure. You would need to compensate for atmospheric pressure (though it doesn't change much anyway) and temperature (as dissolved gases become less soluble at higher temperatures). But we can calibrate against a commercial system then make as many as we want.

The other possibility that occurs to me is to use an iron electrode, which corrodes via a sequence of steps to Fe3O4 (rust). With a suitable cathode the current available would depend on the dissolved O2. Yes, you would have to replace the rusty nail every now and then, but the added iron might be useful biologically.

Don't use your wedding ring as the cathode though :)
Author:  GotFish? [ Dec 22nd, '06, 20:50 ]
Post subject: 
I have a little plc I purchased a few yerars ago, thru DLC direct I think. Wish I had it set up just to monitor temps each day. Its a pain to do it on paper and I haven't been very good at keeping a continous record. Would be great to have a data logger store the data. As far as DO, PH etc just that would be secondary for me if ever. Too may things on the plate.
Author:  njh [ Dec 23rd, '06, 06:33 ]
Post subject: 
I'm using 1-wire to a computer without trauma. It's cost me <$100 all up. You can have as many temp sensors as you like and they all string together. The DS18S20 temp sensor is $4 from arrow electronics. We're working on a 1-wire replacement for my digital water level meter (http://njhurst.com/electronics/watersensor/) so I can measure tank levels over 1-wire too. I talk to the 1-wire bus using OWFS (http://owfs.sourceforge.net/). It is all very low power stuff, and well within reach of anyone not scared of cat5 and a soldering iron.

c.v. http://www.aagelectronica.com/aag/index.html (bit more expensive, but you get a nice case and there are some other interesting sensors there too)
Author:  steve [ Dec 23rd, '06, 10:13 ]
Post subject: 
Ahhh, dallas semiconductor I-buttons ?

I brough in quite a few from the US years ago. Their one wire net is quite good huh? and the RANGE of devices! :shock:
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