Monitoring Water Current direction and speed

bdickens · Post by **bdickens** » Wed Jan 17, 2007 6:37 am

I have gotten involved with a project to monitor water quality in a lagoon. In addition to the usual chemistry fun, I'd like to monitor the water current direction and if possible, the speed. I'm going to need quite a few of the sensors, so cost is an issue.

My current plan is to install about 10 of the sensors throughout the lagoon, and every 2 weeks, pull the bouy, collect the data. So the sensors need to check direction, speed and timestamp every 30 minutes, store it and then allow me to pull them up, download the data to my PC and put them back. Power will be battery.

Before I start tackling this, I would appreciate any comments, suggestions or experience that anyone wants to share. I've done some electronics, but I'm a lot better with software than I am with hardware. Anyone who has a circuit that comes close would be wonderful.

Thanks

Chris Smith · Post by **Chris Smith** » Wed Jan 17, 2007 9:04 am

Before you start remember a single line will spin like a prop, not allowing you to have a set "direction", only a flow?

You will need two or three anchors to aline a set "North and South" reference before you start
other wise you will only measure flow in all directions as it flip and flops.

ecerfoglio · Post by **ecerfoglio** » Wed Jan 17, 2007 9:34 am

Before you start remember a single line will spin like a prop, not allowing you to have a set "direction", only a flow? (Chris)

Or you may use an "hidrodinamic" buoy, shaped so it allways lines up with the current.

Then if you place a compass (electronic) inside de buoy you may log the buoy's orientation which will be the current's direction.

If you add a small propeller and measure itÂ´s RPM you will also have the current's speed.

Chris Smith · Post by **Chris Smith** » Wed Jan 17, 2007 10:14 am

With price as an issue, I didnt want to go fancy or even GPS?

Three lines will hold their place a lot cheaper and easier than the technical stuff, especially when it comes to the multiple bouys.

Dave Dixon · Post by **Dave Dixon** » Wed Jan 17, 2007 11:12 am

I tend to agree with the comments above. The below company does have high dollar stuff, but it you really look around you may find something at a reasonable price to use for your sensors. I get their free Product Handbooks each time they come out. They even pay for shipping, and each of the 5 or 6 books weigh a ton, so there is nothing to lose! They are full of good reference tables, and other information. I would at least order the "Flow and Level" and "Data Aquisition" ones. You might find some ideas within them. Best of luck. See the link here http://www.omega.com/ and free books are here http://www.omega.com/literature/domestic.html
Dave

bdickens · Post by **bdickens** » Wed Jan 17, 2007 1:20 pm

First, thanks everyone for the comments. I hadn't thought of the twisting, but you are right. I can't use GPS since at least two of the sensors will have to be located near the bottom. One area is a freshwater inflow from a lake and the other is salt from the gulf. I'll need to figure out where the flow seperates.

Great source for the flow info. I've ordered their free book.

Keep those suggestions coming. Thanks again

Chris Smith · Post by **Chris Smith** » Wed Jan 17, 2007 1:40 pm

Watch out for "Omega's" sticker shock!

Robert Reed · Post by **Robert Reed** » Wed Jan 17, 2007 4:28 pm

Just one thought on floating buoys. In a life time of boating on fairly rogh water (lake Erie), whenever under anchor, the boat ALWAYS rode to the wind and not current or waves. I guess you could consider the boat as a buoy in these cases.

haklesup · Post by **haklesup** » Wed Jan 17, 2007 4:55 pm

You may find it more economical to have one data acquisition system linked to each bouy sensor by RF link. the RF uplink will cost less and use less power than a DAQ per sensor and you won't have to sail to each bouy weekly to get the data. A multichannel reciever may run a bit more but thats the tradeoff.

Is it safe to leave equpment onshore unattended, is there a locked building on site? If not, this requires some memory in the bouy to save data until you come to retrieve it.

In addition to direction and current, you could also easily measure temperature and clarity. Once you have a PIC in the BOUY to acquire, A/D, format and transmit the data, adding another channel to the A/D is not too much trouble.

There are many vendors if you search on "DAQ systems"

Dean Huster · Post by **Dean Huster** » Wed Jan 17, 2007 8:26 pm

Don't stop with just one. Get all of Omega's books/catalogs. They're free and chock full of all sorts of information and tables. And Dilbert cartoon strips. They're available on CD, too, but often times, the CD version of things is a lot more difficult to use, provides no space for notation and sometimes is not as complete.

Dean

Lenp · Post by **Lenp** » Thu Jan 18, 2007 4:55 am

Would it be feasable to construct a tripod from pipe or rod, driven into the bottom of the lagoon or with concrete anchoring weights, with the sensors fastened to the legs, at approporiate points. Install a water proof junction box (NEMA4) at the top with a connector for easy data recovery and battery changes. I would not expect that the tripod will twist, and with the sensors attached, measurements should be more accurate. Possibaly this will be a lower cost than a floating/anchoring system. You might need a flag or beacon as a warning marker as well, on any method.

Len

bdickens · Post by **bdickens** » Thu Jan 18, 2007 6:37 am

Good thoughts. My house happens to be on the lagoon so I have a secure spot to monitor from and as it happens, my neighbor (who drafted me into this) has line of sight to the entire lagoon (peninsula) so I could always monitor from that point. I didn't think the RF would work over 8 miles of lagoon (but thats a lack of experience on my part) Would it ? That would make my life easier if we can do 8miles.

Good thought about tripods. I will have to mark them by bouy and the main sensors will be down about 3-4 feet. I will probably lose 1-2 through the season. I also agree, if I end up with a pic or the like I can monitor temperature and a few other things at the same time. Maybe even pull in pressure changes (depth?). As in an earlier post, if I make the package hydrodymanic, I could use it like a weather vane and pull the direction from a solid state compass.

Thanks all for the posts

dyarker · Post by **dyarker** » Thu Jan 18, 2007 9:00 am

Consider a Zigbee net. They don't reach 8 miles, but they don't have to. Each one sends it's own data back, and acts as a relay for bouys farther away.

haklesup · Post by **haklesup** » Thu Jan 18, 2007 12:12 pm

8 miles does pose more of an energy conservation problem when it comes to real time RF. You do have a clear line of sight going for you at least. 4W FRS type radios might might make it but how would you interface and make them come on for only a moment while you transmit the daily cache of data. More frequent updates = more frequent battery changes unless you can work a solar array into the project. In any case, without real time transmit, you'll need memory and a controller at each buoy

Something to try: Can you receive an IR remote control signal through a telescope at that range. Simply use your CCD camera or cell phone camera up to the eyepiece for a quick test. Each buoy could simply repeat its data for the day over and over via an IR LED beacon which you observe daily from afar (probably after dark).

bdickens · Post by **bdickens** » Thu Jan 18, 2007 2:19 pm

I hesitate to add solar cells to the project just because it would make the bouys a bit of a theft target, although I can work around that if I have to. My wife wondered if I could genrate electricity from the current flow, but that seems more complex than the cells.

A telescope for infrared is clever. I certainly would not have thought about that.

I'm going to check out the Zigbee. I can have a pretty big battery pack and from my RC electric airplane hobby, I certainly have enough chargers.

Anyone got opinions on processors or packages that would seem to do what I need. I've been using my OOPIC but thats clearly overkill X 10.

Thanks

T&L Publications