trying to select materials for a liquid probe

Taylortronic

hello, parallax stamps in class forum readers. i am trying to build a circuit inspired by Chapter 5 in the Applied Sensors text. my design involves control of a 5 gallon bucket, but i am concentrating on the measurement aspects specifically right now and i want to be able to gauge water level, temperature, EEC and ph.

so here i am trying to concentrate on one at a time and i'm working on water level. if the sensor is going to include low levels the probe is going to have to be almost a foot and a half, so i'm hanging two steel threaded rods. should i stick with stainless steel? and what gauge wires should i use to connect the probes to the circuit? is it possible to get all these measurements using different circuits connected to the same probes?

Chris Savage

Hello,

·· You are wise to explore each individual sensor method individually.· This also answers your question though about using one sensor for everything.· That's not going to happen.· The proper probes/sensors for your needs will be somewhat dependant on the contents of the container as well as the environment.· After all, if you're outdoors you'd want sealed sensors.· Is the tank going to be sealed, will the contents slosh, is there pressure, etc?· I would concentrate on one sensor at a time, combining aspects when needed.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Taylortronic

okay. this project involves mixing nutrients for my garden. i figure that's a pretty standard application. my design involves a couple five gallon pickle buckets and i have to know some things about the mix before it goes to my plants. i have to know the liquid level in the buckets first of all and that's where i'm at right now. the liquid would be probably 98% water and a mix of nitrogen, potassium and phosphorous.

as elements are added to the mix bucket (through automation) i'm planning to program compensation to keep the levels steady. some mix goes to the garden (this is not a scheduled event but based on input) and the level goes down to a trigger point where the program adds the right mix to get the level back up.

the bucket won't be pressurized and (except for a few vents that will allow for air displacement in the bucket) the bucket will be sealed. the level will be changing but it will be upright at all times, so no sloshing. i'm pretty sold on the probe example in the applied sensors text and i'm specifically interested in how i can apply it to a five gallon mix container (standard bucket, you know the type).

thanks for the help,
taylor

Tracy Allen

The probe in the text measures a combination of the water conductivity and level, and in a fertilizer mix those will, it appears from your description, be changing simultaneously. You may want to use one probe as a point contact for the high level, and another for the low level. Making it a point contact takes the conductivity out of consideration. If you want a measure of conductivity (to keep tabs on the sum total of fertilizer added), then make a separate probe that is always immersed near the bottom of the well stirred bucket, along with a temperature probe.

With regards to these specific questions:
<<should i stick with stainless steel? and what gauge wires should i use to connect the probes to the circuit? is it possible to get all these measurements using different circuits connected to the same probes?>>

Yes, use stainless steel for the probes. The fertilizer mix will be pretty caustic!
The currents in the wires are small, and the wires should not have to run far (?!), so the gage is not too important. Say, 22 gage. I don't know exactly what you mean by the 3rd question. One probe will not be able to make all of the measurements, and I certainly agree with Chris that it is best to try out one probe at a time and get it working before tackling the whole system. It should be possible to mount all of the probes on one support such as the SS threaded ground rod.

Does that help? Maybe there is more about your planned automation that needs a complete analog level sensor?

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Tracy Allen
www.emesystems.com

Taylortronic

thanks again. yes, i'm gonna have to get realistic about the probes. what i really want to do is add mix based on levels and so i am going to have to find a dynamic level probe instead of just setting up two triggers eventually. but i've taken the time to actually set up a trigger system and i've got it working so that is a help - progress is the best motive for more work.

thanks again and big up to all the parallax forum readers and moderators!

taylortronic