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#1
11/15/2007, 09:59 PM
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Need help with DIY Controller Probes
I am building a controller for a senior design project. I have been looking for probes but none of them have data sheets about their specs. For anyone who has build a controller before, how did you figure out the probes. I mean about amplification, output, impedance) Did you do trial and error? I need some help please.
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#2
11/16/2007, 08:04 PM
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There are many probes for industrial use with 4-20ma output.
We don't know what the heart of the controller is? A Pic, PLC, raw logic gates, etc..??? More explanation may help us, help you.
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"Sharks are naturally peaceful." "How'd you get that nasty cut anyway?" "A shark bit me." Jack of all trades, and master of none. ~Steve~ Last edited by funman1; 11/16/2007 at 08:17 PM. |
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#3
11/16/2007, 08:12 PM
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Please post the details of your project and we can help you get a probe interfaced.
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#4
11/18/2007, 07:03 PM
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The controller will basically read pH, ORP, Conductivity and Temperature and control various electrical outputs. The controller will be based around either a Atmel ATmega microcontroller or a Cypress PSoC microcontroller. I need help getting probes that can be interfaced to the microcontrollers ADC after the proper signal conditioning. The problem is I dont know how the probes will operate or their specs or where to get them. I spoke to a professor who told me they can work linear or non linear. Their output based on the water can vary by either voltage, current, impedance, etc. After I figure out how they work, I can choose the proper conditioning. I also have no idea where to buy the probes. Thanks for the help guys.
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#6
11/18/2007, 08:16 PM
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Most probes have a standard output. A quick google search will provide you with a few large manufacturers.
Probes are high impedence, so they act like voltage sources. The probe will output a voltage dependent on the PH. The ORP and Conductivity probes will do the same. You can change this into a current reading if you like. In most cases your instrument amp is used to convert the output to a 4-21ma range (as funman indicated). That is a standard for most commercial and lab equipment. http://www.sensorex.com/support/educ...education.html Here are some aimed at hobby and education: http://www.vernier.com/probes/ They come with an amp. Cole Parmer http://www.coleparmer.com/catalog/pr...x.asp?cls=3527 Omega http://www.omega.com/products.html Milwaukee Instruments Cypress http://www.cypresssystems.com/Electr...Electrode.html Hanna Instruments Fisher Extech Mettler Toledo |
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#7
11/19/2007, 12:10 PM
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Chances are good that you're going to need an amplifier to get the signal readable by the controller. The amplifier will also allow you to monitor smaller variances in sensor output. You'll also need to implement analog to digital conversion on most signals coming into the microcontroller. Most of the time you'll be reading voltage differences, not current differences.
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A wise lumberjack always has a sharp saw. |
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Linear Mode
