Water pressure sensor reccomends?
Jonathan
Posts: 1,023
Hi All,
I'm looking for a pressure sensor to measure the level of water in a 2500 gallon tank, aprox. 10 feet of water or about 4.3 PSI of pressure. I've fooled around with DIY capacative sensors in the past and they drift over time. I'm hoping for sub US$50 and will go as high as $100 if need be. I've seen some automotive ones that might work but resolution would be low. 0-5 V output would be nice, but I'm willing to work with any type of output.
Thanks!
Jonathan
I'm looking for a pressure sensor to measure the level of water in a 2500 gallon tank, aprox. 10 feet of water or about 4.3 PSI of pressure. I've fooled around with DIY capacative sensors in the past and they drift over time. I'm hoping for sub US$50 and will go as high as $100 if need be. I've seen some automotive ones that might work but resolution would be low. 0-5 V output would be nice, but I'm willing to work with any type of output.
Thanks!
Jonathan
Comments
However, maybe have a look at the following???
http://www.digikey.com/product-detail/en/40PC006G2A/480-4252-ND/2832020
These sensors listed below, which output 50 mV, etc. could be run into an ADC, for example, or simply have their signal amplified:
http://www.digikey.com/scripts/dksearch/dksus.dll?FV=fff4001e%2Cfff800b3%2Cfffc01e0%2C24001fb&k=pressure+sensor&vendor=0&mnonly=0&newproducts=0&ptm=0&fid=0&quantity=0&PV218=4&stock=1
Thanks a ton, at least it's a possibility.
Jonathan
The data sheet for P1 also goes on to say "media must be compatible with epoxy adhesive." You should definitely check with Honeywell for whatever your application is, but I'm guessing normal water would be okay with that. If you can use a small diameter pressure line leading from the bottom of the tank to your sensor, then perhaps you can leave the line full of air, or at least partially full of air, so the contact at the sensor itself is mostly damp air. If you keep the line full of air, you might need to make some small adjustments for temperature variations and compressibility of the air - much of that depends on your particular set-up.
Also, if you're sure that the tank level changes less than the full 10 feet, then you could use sensors with a smaller range and better resolution. Or, you might find that the differential pressure sensors work better than the gauge pressure types. Hope that helps.
If it's as wide as it is tall, you could use a float on a lever.
I recently started working on my magnetic encoder project again, and I realized one possible use for these encoders would be a sort of water proof poteniometer. The encoder chip and other electronics could be sealed in a water proof enclosure and the magnet would be allowed to pivot above the senor chip on the outside of the enclosure. This would require some means of holding the magnet over the sensor while still allowing the magnet to pivot.
The magnet would be attached to one end of a rod with a float at the other end. The float would cause the magnet to rotate which rotation would be picked up by the sensor. Depending on the thickness of the tank material, the encoder sensor could be mounted on the outside of the tank.
Just thinking out loud (with my fingers), what about some variation of a float with magnet. You could have reed switch or hall-effect sensor in a line down the side of the tank. On the inside of the tank use a magnet attached to a float that travels up and down a tube next to sensors. You might have a hard time getting good resolution this way but I'd think it wouldn't be hard to within six inches of the actual fluid level (assuming you use 20 sensors).
Have you tried an ultrasound sensor? They're pretty easy to use. Just mount it above the liquid pointing down.
There's also all sorts of laser and light sensor set ups that come to mind when I start thinking about ways of measuring liquid. I think I recall PJ Allen having an idea of how to measure a liquid with a laser and light sensors.
If you describe the tank (and liquid) in more detail I'm sure we come up with a lot more harebrained ideas.
I don't think that would be an issue. If the air warms up and expands it will push the water in the tube down a bit and will equalize with the water level in the tank.
Imagine a clear plastic tube 10 feet long, the top of which is sealed with a pressure sensor, and the bottom of which is wide open.
Now imagine submerging almost the entire 10 foot long tube straight down into the water. You take a deep breath and dive into the water and swim down to the open end. Because the water pressure has compressed the air somewhat, you will notice that the water level inside the tube is not at the open tip of the tube but is instead Y inches higher than the tip, at a point we'll call PY.
Question: is your pressure sensor measuring the water pressure at the level of the open tip of the tube or is it measuring the pressure at the same level as PY?
Imagine you are under water holding a piece of tubing that is full of water and sticking 5000 feet straight down toward the depths of the ocean. If you now screw that 5000 foot long tube onto the end of your 10 foot long tube, will the measured pressure jump to a reading equal to 5010 feet of water depth?
As to ultrasonic, I've used plenty of them, but I haven't found a waterproof module. I could work with just a waterproof transducer, I have built ranging systems with my own driver and receiver before. Seems like there ought to be a simple pressure sensor that would work. I have played with pots and floats a long time ago but had the same issue of not finding a sealed pot to resist water damage.
I'll contact Honeywell and see what they say.
Thanks a ton for the input folks! Keep it coming, there has to be a decent solution for a common problem.
Jonathan
As to ultrasonic, I've used plenty of them, but I haven't found a waterproof module. I could work with just a waterproof transducer, I have built ranging systems with my own driver and receiver before. Seems like there ought to be a simple pressure sensor that would work. I have played with pots and floats a long time ago but had the same issue of not finding a sealed pot to resist water damage.
I'll contact Honeywell and see what they say.
Thanks a ton for the input folks! Keep it coming, there has to be a decent solution for a common problem.
Jonathan
How about this: you have a pole made of clean PVC. At each one-foot interval, you've got a float with a sealed magnet on top and a sealed Hall effect switch suspended above it. When the water level rises, it raises the float up a couple inches until it bumps into the Hall switch. The switch then sends a signal to whatever your system might be. When Hall switches 1, 2, 3, 4 are active and switches 5, 6, 7, etc. are not, then you know your water level is somewhere above 4 feet but below 5 feet. Everything is sealed, nothing moves but your floats (each one just a couple of inches), your resolution ain't great, but might that work well enough?
I was thinking of mounting the ultrasound sensor above the water, pointing down. I wouldn't think it would need to be water proof. Just use it to measure the distance to the top of the water.
If you decide to measure air pressure in a tube as suggested by EA, I think one of these pressure sensors would be a better choice for your purposes than the Honeywell sensors. Besides costing less, they measure differential pressure so changing atmospheric pressure shouldn't give you false readings. It only has a 0.3psi range which I believe translates to about 9.6 feet of water (I seem to remember 1 atm is about 32 feet of water). You'd connect the sensor to a tube full of air that reaches down to the bottom (or near bottom) of your tank.
I have a couple of these sensors myself I've been meaning to use them to measure airspeed of my radio controlled aircraft.
Never mind. I was thinking 0.3 atm not 0.3 psi.
I'd go with Duane Degns' recommendation. It's a little more than you want to spend but it's well worth it. Here's a link to the one I use for measuring the water level in our public water reservoir. The serial output is good, works with propeller without a hitch. And you can get a temperature compensation sensor with it as well (I also use it for better accuracy throughout the seasons.)
http://www.maxbotix.com/Ultrasonic_Sensors/MB7386.htm
However, if you like the ideas involving tubes and have a fish tank bubbler, you can route your output of the bubbler through a Tee connection.... one outlet of the Tee connects a tube that goes to the bottom of your tank with an airstone on it. The other connection of the Tee connects to a pressure transducer. The bubbler pumps away and the tube builds up X amount of pressure depending on the water level- Higher water level=higher pressure in the tube... This will let you put your transducer anywhere you want, and you "calibrate" the pressure at the transducer by adjusting the height of the transducer relative to the bottom of your tank. The transducer can be replaced with a pressure switch for on/off signals at X water level. Here's a link to a typical air pressure switch that could be used (Double check the psi limits, etc) http://www.grainger.com/Grainger/CLEVELAND-CONTROLS-Air-Sensing-Switch-6XPX7?Pid=search
Robert
Although I wasn't really thinking about switches, as opposed to a sensor. A low level alarm would work, I don't really need to know tank level, just when I have a problem. Maybe I'll look into that.
But I do wanna play with the cool weatherproof sensor now!
Jonathan
Do you really need a weatherproof sensor?
Maxbotix sells nice stuff but there are lots of inexpensive ultrasound sensors. They're plenty cheap enough that you could try a few to see if they can handle the environment of your tank.
If need be you could replace the normal transducer with a waterproof one (fourth one down the page). I'm not sure if you'd need to modify the circuit to use a waterproof sensor or not.
Yeah, I do think it's going to need to be weatherproof. The working end is hanging in a water tank, a high humidity environment if there ever was one. Then it needs a sealed run back to the pump shed for the wiring. I'm guessing that substituting waterproof transducers will reduce range, because I bet you have to drive the sealed ones harder to make the same strength sonic signal.
I'm leaning towards the US sensor, even though it ain't cheap. It's going to be easy to install and should last for years. I need a rock solid solution that will stay on the job, I'd have to truck in water if I had a well pump failure and didn't know until I ran out of water. . One nice thing about the US sensor as opposed to a switch is that I can verify that if the well pump is running that the tank is actually filling. I'll also be able to double check the flow sensor by calculating fill rate and total gallons from the US sensor.
There, I just talked myself into it. I'm going to go order. Thanks to all!
Jonathan
Please keep us posted on how well this works out for you.
Thanks all!
Jonathan
http://www.goldmine-elec-products.com/prodinfo.asp?number=G15473
Awesome. Now we'll see how long it lasts. Thanks for the help folks, I feel like I got the right sensor for the job.
Jonathan
The reason I ask is because I'm also in a rural area and I have three 5000 gallon water tanks I'd like to add a sensor to measure the water levels.
Jonathan
Jonathan
Glad to hear yours is working out well. Same here. Question for you: How have you attached the leads to the sensor? I went with screw type terminal blocks, so that I could easily disconnect the sensor without needing to remove the control cable, etc.... did you just solder your leads to the sensor board?
Jonathan