Help Needed- Conductivity and Flow detection of water
B-EZ
Posts: 5
Greetings-
I am an independent designer who is trying to create a device that I can use in my cities sewer system. The goal of my design would be to lower this device into the storm sewer and have some sort of circuitry that is able to detect what the height (flow) of the system is along with the conductivity of the water. After this data has been receieved I would then want it stored to a USB device. I would ideally prefer this device to take random samples throughout the day (say 3 times for 10 minutes a day).
My ultimate goal is detect anyone who may be dumping waste into our sewer systems. I am not very· familiar with all of the circuitry on this site so I would appreciate it if I could get some insight as to what I should be looking at. I would be looking at schematics and sensors to purchase as well as how to implement much of this.
I know that this is very broad but I am looking to find some people that could give me some good advice to get the ball rolling. Any help would be nice.
As a disclaimer I should say that I am fresh out of college and am low on funds...so a cheaper design would be preferred over spending a lot of money.
I am an independent designer who is trying to create a device that I can use in my cities sewer system. The goal of my design would be to lower this device into the storm sewer and have some sort of circuitry that is able to detect what the height (flow) of the system is along with the conductivity of the water. After this data has been receieved I would then want it stored to a USB device. I would ideally prefer this device to take random samples throughout the day (say 3 times for 10 minutes a day).
My ultimate goal is detect anyone who may be dumping waste into our sewer systems. I am not very· familiar with all of the circuitry on this site so I would appreciate it if I could get some insight as to what I should be looking at. I would be looking at schematics and sensors to purchase as well as how to implement much of this.
I know that this is very broad but I am looking to find some people that could give me some good advice to get the ball rolling. Any help would be nice.
As a disclaimer I should say that I am fresh out of college and am low on funds...so a cheaper design would be preferred over spending a lot of money.
Comments
good luck
The height would probably be the easiest using a ping device (ultrasonic range finder). The conductivity on the other hand is not that easy. You need some way to sample the conductivity of the water, and that usually involves touching it. With water hieght changing, you run the risk of loosing or flooding the device (neither of which would be a good idea).
I would propose you use some kind of storage device that is easier to interface with. Anything USB based is pretty complicated to communicate with. If you used a Propeller you could interface directly with an SD card (with a holder of course).
I'm not big into the science of testing for properties, but if you can deduce conductivity with electricity (seems logical), then a simple RC time circuit would probably work ok as well. (Where is Tracy Allen when you need him). You may want to look up EME systems (google). He does all kinds of Ecological type stuff.
www.emesystems.com/BS2index.htm#webRing Here is the proposed item I was thinking about.
James L
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James L
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Lil Brother SMT Assembly Services
Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!
Post Edited (James Long) : 1/27/2010 11:50:42 PM GMT
First of all, you need to determine at what point in the system are you planning on placing sensors. This will affect your decisions about the sensitivity of the sensors. For example, if you want to monitor things going down a specific roadside drain, then your dilution will be one thing, but if you want to monitor a 10 foot diameter sewer pipe that is fully loaded and flowing at 5 feet/second and draining an entire square mile of housing development, then you'd need some kind of different sensor because of the immense dilution problem. Furthermore, depending on what sort of substances you want to monitor, not every chemical will greatly affect conductivity. Or, as in the case of an oil, such chemicals might only affect conductivity near the surface of the water. If they are salting the roads because of winter conditions, your sensor might get saturated and never see a pollutant, etc. You also might have to take into consideration temperature effects, ice and snow, and solid debris.
The Basic Stamp or Propeller systems sold by Parallax can be used to run a system like the one you're talking about, but you really need to sit down and define precisely what you're looking for (and what you are willing to not look for). In short, there's no cheap, single system that can detect every possible thing that somebody might dump into a sewer system. Another option, if you have specific violators in mind, is to use photographic monitoring of potential dump sites. You might even have something like syringe pump stations that could automatically and periodically suck up samples that could later be analyzed in a lab and correlated with photographic evidence. Again, the Basic Stamp and Propeller could be used to control a device like that, but you'll need to learn about timers, actuators, etc.
hope that helps "get the ball rolling."
http://www.globalw.com/products/fc200S.html
http://www.cascadia-instrumentation.com/id24.htm
http://www.sensorsmag.com/sensors/acoustic-ultrasound/ultrasonic-flowmeter-basics-842
Post Edited (AJ-9000) : 1/28/2010 7:20:19 PM GMT
Any further input would be great.
http://www.tracomfrp.com/flumes.htm
some plans and info for making your own flumes...
http://aces.nmsu.edu/pubs/_m/m-226.html
http://aces.nmsu.edu/pubs/taskforce/water/WTF_3.pdf
i remember reading not too long ago that parallax is going to come out with a more moisture resistant ping))) sensor, with a solid face instead of the screen fronts. these i think would work great for this, providing you protect the electronics of the sensor with some sort of case.
Conductivity to·detect the presence of·pollutants·is a entirely different animal, as you have to compensate for temperature of the water tested,ph, and most probes have to be "zero'd" against a standard, say deionized or distilled water between readings, thos meters basically reads the voltage drop between two probes in the water being tested. here is a link for more info...
http://www.epa.gov/volunteer/stream/vms59.html
i would suggest finding a premade conductivity meter/sensor that has rs-232 outputs for data collection, because making one (or attepting to) that would be·accurate would just make you pull your hair out, kill baby kittens and make the hole in the ozone layer bigger just trying to get the accuracy down to an acceptible level. Also the epa may mandate that the sensor be certified and calibrated with documentation on a regular/yearly basis, depending on local and federal laws.
then you could access that data with the prop or basic stamp then save it to a usb device with the usb datalogger that parallax sells.
Post Edited (kf4ixm) : 1/28/2010 8:56:47 PM GMT
You drill a small air hole near the top of the pipe, but well below the sensor. This serves two purposes. It dampens the rate of change of the water level from wave action and it protects the PING from direct contact with the water because it lives in a bubble. The ones I saw were made with 2" PVC. You could also use a screw on top to place the USB stick, batteries and a processor in an air tight container sitting above the sensor shaft.
For conductance you could use some aluminum coated tape on either side of the inside of the bottom of the pipe with wires running down the inside. This assumes the conductivity of the water is high enough to be measured without a fancier rig.
Sealed, selfcontained, tuff, mounting parts are at home depot and its cheap!
Sounds like a fun project! How many do you want?
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Send $1 to CannibalRobotics.com.
I am just goingto make one prototype for now and see what the city thinks.
The two vertical white tubes are stilling wells as described above, but larger, and there are horizontal channels into the flume at the bottom to sample the water level. Each stilling well has a float with a beaded cable and counterweight, and the cable passes over a wheel that turns an encoder that delivers one pulse for each 1 mm of change in the water height. These things (instrument from Unidata, Australia $$$) are very accurate and stable. The one at the far downstream end of the flume is the one that is most important for gauging the volumetric flow of water. On the near end, there is a turbidity probe that monitors the cloudiness of the water due to particles. The mercury is bound to particles, so knowing the particle concentration, the % of mercury, and the volume flow rate, the project can monitor how much mercury is moving toward the Pacific Ocean. There are calibrations that involve sampling and lab tests, but having those, the automated instruments give a continuous record.
The effectiveness of a sampling scheme depends on what you expect to detect in the water. Conductivity may show some things. In natural streams, low conductivity usually goes with immediate runoff from rainwater, and the conductivity is higher in rainwater that has been sitting underground for a while and has picked up minerals and salts. Then there are things like agricultural fertilizers. Turbidity is a good surrogate for detecting erosion and muck and the stuff that clings to it. The turbidity meter shines a light out into the water and measures the scatter from suspended particles, albeit, course particles like sand and silt have very different properties from particles like clay.
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Tracy Allen
www.emesystems.com
I've been working on a water level sensor for monitoring stream flow using a MaxBotix ultrasonic ranger (about $50) and a verison of the Scott Edwards Data Collection board built on a Basic Stamp 2 Carrier board. The sonar type sensor was selected because it is not in the water and can be mounted well above the water. We have flash floods and ice to contend with. It seems to work well in so far during below freezing weather. If you are interested I can provide more info.
Bob Smith
That sounds great! I would love to know everything/anything you can tell me about what you have going on. I live in MI so the conditions that I would be working in sound just about what you see wherever you are at. I would literally like to know anything you could tell me, this would range from the type of code you had to write on this all· the way up· to what/where you are storing your data. I am in the midst of searching through different ping))) sensors for this application because they seem the most cost efficient. As stated, any help would be great!!
As for the eLiquid sensor that is something I flirted with awhile ago but I do not think it will be big enough for my application. I would need something that could work with higher waters than what is offered. I have searched around other places to see if they makes longer versions of this sensor because I think that implementation would be fairly simple.
Once again, thanks for all the help and keep it coming!!
There can be ambiguity in reporting water surface height. It is not a problem with a still, flat surface like a tank or stilling well, but in an uneven channel the flow makes the water slope locally with eddies or choppiness. This is a big problem in natural streams where there are natural eddies, but in a storm sewer it might be possible to find a nice straight stretch with even flow.
A sensor that dips deep into the flow has its own issues. For example, in a stream with a 3cm cylinder (a capacitance depth sensor), all is well when the water is 10cm deep, but when it is 1m deep and running fast an furious, the readings average high and have a 7cm standard deviation, due to turbulent water piling up behind the cylinder.. That is why stilling wells are put off to the side with a sampling tube at the bottom coming in at right angles to the flow. And that is why too that the ultrasonic method is attractive, a non-contact measurement. I've see ultrasonic sensors that measure both the depth and the average velocity (Doppler) of flow, but those are expensive.
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Tracy Allen
www.emesystems.com
Post Edited (Tracy Allen) : 2/6/2010 7:10:17 PM GMT
Thanks again.
I'm sorry but since our BIG snow storm I've been otherwise occupied. If it's not too late here is a set of drawings schematic and layout for the Stamp carrier board and wire wrap that I've used and the code as it stands. In the mean time I've received a pair of XBee tranceivers and just tested them in the default transparent mode and they work but don't know about range. My problem now is no more program memory space and how to make an enviormently rugged version. Either I'll go with making a PCB board or rewrite the code and use the OWL2pe (which appears to be the best course).··I hope this is usefull and let me know if· I can provide any other info.·I've done limited testing during the winter for up to 5 day periods with rain, snow, floods·and tides.
Bob Smith