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Cheapest way to measure water depth

Cheapest way to measure water depth

Cheapest way to measure water depth

(OP)
I am interested to measure the water depth in a tank above a reference point. The water depth or pressure varies above the reference point from 0 to 2.5 meters. How can this be done in a cheapest way without buying expensive piezometers and data loggers?

RE: Cheapest way to measure water depth

Without more data your question is essentially unanswerable.

Do you want remote electrical data or a big pointer on a stick which is read locally?

If remote do you want a continuous readout on a pc?
Is the pc local to the tank or miles away?

RE: Cheapest way to measure water depth

sight glass
connects to side of tank, liquid fills glass, look at the glass, see the liquid level, know the height.

RE: Cheapest way to measure water depth

Gems also has a yard stick on a float.

Dan

RE: Cheapest way to measure water depth

Expensive is different to different people. Water has weight and you can measure the depth of water with a pressure gauge/sensor.  In the same vein, a tube can be stuck in the water and air pressure can be applied to the tube.  The prssure remains constant at the point where air bubbles out of the bottom of the tube.  Great for liquids that are dirty.  Often people don't need what they think they need.

RE: Cheapest way to measure water depth

Cheapest way would be a suitably long length of wood with depth graduations in the unit of choice.

RE: Cheapest way to measure water depth

Ah yes, the legendary "compendium": 'Depth of water sensing'

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Cheapest way to measure water depth

"Ah yes, the legendary "compendium": 'Depth of water sensing' "



Shall we start again?

First bore your hole...

RE: Cheapest way to measure water depth

I disagree with Warpspeed!

I suggest that a cord, with knots tied on it attached to
a mass with a density somewhat more than that of the
surrounding water be used.  After insertion, an operator
can yell out something like:

"By the mark twain!"

Where is your sense of history for Gosh sake! Besides,
have you priced wood lately?

  Cheers,

   Rich S.

RE: Cheapest way to measure water depth

Zounds !!  

Beaten once more by a superior intellect.

RE: Cheapest way to measure water depth

You guys must be speaking about Keith!

BTW, I'll have the applications page with the PLC on
it on my server in the next day or two Keith.  Due credit
to you too!

Sorry, this is a little off topic.

  Cheers,

   Rich S.

RE: Cheapest way to measure water depth

Staying off track since the OP is missing in action.
Rich, That your SingleChipPLC?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Cheapest way to measure water depth

(OP)
I would like to thank you all of you for your reply. BTW I have gone through the "big" discussion about water depth sensing in this forum ....http://www.eng-tips.com/viewthread.cfm?qid=58310. After going through every post with a lot of pain ... I really couldn't find what I want ... that's why I posted it again.

The tank is inside a laboratory and the pressure varies in every 5 or 10 minutes during the experimental set up. The experment can run for 1 day. Obviously a man standing and recording the pressure variation is not a reasonable solution .. if the experiment is repeated for a lot of time.

Regarding the reading, it is continuous and I prefer the data to be saved and downloaded latter to my pc. If this is not alternative, It is also good to connect the pc to the measuring device continuously and record it at every time.

I want an automated and cheapest way to carry out this duty. From my search so far the pressure sensors are preferrable but when I check the price really it is not affordable for me. Can anyone suggest me a solution please.

Thanks in advance for every contribution!

RE: Cheapest way to measure water depth

While you could spend a lot, I don't see an acceptable pressure sensor  and data logger costing more than $150.  Is this what you call expensive?  

RE: Cheapest way to measure water depth

I don't think you are going about this the right way: nowhere have you mentioned the accuracy to which you must know the depth of water - at the very least doesn't the tank have an ordinary ball valve to control the water level? .

You say you want to automate the logging of the readings: if this is such an important parameter which must be understood (and probably controlled at some point)then how can you afford not to make accurate measurements by using the appropriate sensors? Either it is important to whatever experiment you are conducting or it really isn't!

RE: Cheapest way to measure water depth

You take a Pentium-based PC onto which you attach a solid aluminum bar as a heat sink, one end at the top of the Pentium chip.  You suspend the PC until the tip of the aluminum bar reaches the lowest measurable point.  Water acting as a heat drain, the higher the water goes the cooler the Pentium becomes.  With your monitor at the top of the hole, you go into the BIOS and measure the temperature of the Pentium.  Then you use a videocamera to record the data.  Hey where's my price for the latest application of a Pentium? smile

But seriously, what is your budget?  There are stainless steel pressure sensors out there for $100.  You will spend much more in your time spent writing your test procedure.

RE: Cheapest way to measure water depth

O.K. To get serious here.

There are a lot of pressure transducers out on the market
for 0-7 psi.  Some are available from I believe Jameco
for 0-1.45 psi.  These are all in the under $20.00 range
and I believe are used for automotive applications.  Large
volume ==> low price.  Usually they don't have very
robust enclosures, but that might not be the issue.

Piece together the following link:
http://www.jameco.com/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&catalogId=10001&langId=-1&categoryId=352540

Someone earlier mentioned a "bubbler" method of doing
depth of tank monitoring. This requires a low pressure outside air source.  One might be interested in looking
at deep tank aquarium air pumps.

A small needle valve can be placed at the output of the
air pump.  This feeds a "tee" connector which has a
tube to the bottom of the tank (or the lowest pressure
that one wants to measure).  The other side of the
tee goes to the inlet of the pressure sensor.  The
valve is adjusted until there is a small stream of
bubbles (hence the name) coming out of the tube on the
bottom of the tank with the tank full.

The amount of pressure on the inlet to the pressure sensor
will be proportional to the depth of the fluid in the
tank.  Excess pressure from the air supply will come out
the bottom. So, there will be a greater pressure with
the tank full vs. when the tank is empty.

The bubbler does NOT take into account the density of
the fluid, therefore, if you are changing the components
or concentration of the fluid, a variance will be
observed when tank levels remain the same.  This usually
isn't much of a problem in many applications.

Feed the output of the transducer into a suitable
insturmentation amplifier, then to an A to D converter.

The suggestion of using a PC is a pretty good one. One
can easily find A/D converter boards for the computer
along with suitable MATHLAB type software.

MPJA has some low cost 0-7PSI sensors available for
under $5.00 however, I had to build an enclosure for
it.  The inlet is a bare hole.

I have two versions that I used:
1. I epoxied a "nipple" from a water drip system onto
   an ordinary water faucet washer. I then *CAREFULLY*
   epoxied the assembly to the pressure transducer, making
   sure that I did not plug the hole.
2. Turned an aluminum enclosure for the transducer with
   my lathe.  Much more robust..... Turned that $5.00
   sucker into a $100.00 type.

OPPS! I see MPJA is out of them. Well, it is a surplus
house..

Hope the other stuff helps.

  Cheers,

   Rich S.

RE: Cheapest way to measure water depth

O/k being serious here. A pressure transducer is a good solution, but the cheaper ones will need some sort of amplifier to give a signal of usable amplitude. There may still be problems with long term accuracy and drift, and the results may not come up to expectations.

A very simple, low cost, and accurate depth measurement can be obtained with a float, a drum, and a ten turn potentiometer.

The required travel is 2.5 metres, the circumference of the drum would be 250mm, or around 80mm diameter. Don't laugh this is an entirely practical solution.

The typical linearity of multi turn potentiometers, even the very cheap ones is excellent, and if you wrap several turns around a grooved drum there will be no slippage. The voltage can be scaled to read directly in whatever engineering units are most suitable.

I have had great success with the plastic coated very fine, stranded stainless steel wire sold at fishing supply shops. This is used by fishermen to prevent fish from biting through the last few inches of line. This wire is light, flexible, incredibly strong and absolutely will not stretch.

Find someone that can turn up an suitable drum on a lathe with about a fifteen turn helical groove that will seat the wire. A light counterweight on the free end, and you are in business.

RE: Cheapest way to measure water depth

I think we have demonstrated the huge range of possibilities here for measuring 'water level'.  Now I think it is time for yalew to get-off-dead-center and start being specific to the point that useful  discussion can commence.

To wit,
Define:

a) Pressure/depth?

b) Closed tank or open?

c) What data rate do you actually need? You realize all this data needs to 'handled',  so never exceed what you 'need'.

d) What is your actual budget?  "Too expensive" is not a budget.

e) Are there any threaded ports in the tank below the lowest required depth?

f) What is the tank made of?

g) In what format do you need the data?

h) If you are going to run the entire experiment using a PC, why would you want to add the complication of having to time stamp the data so it has relevance once you bring it to the PC?

i) What power is available?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Cheapest way to measure water depth

(OP)
I would like to thank you every body again for contributing alternative solutions and suggestions. To put it in a nut shell, I am interested in the following alternatives so far:
1.  Using pressure sensor as suggest by Riches … thanks Rich! I would be glad if I can buy a pressure transducer with cost of less than $20. Rich can you give me a link or example how I can use the pressure sensor and the data logger together to get the pressure which I want.

2. Using float, drum and potentiometer as forwarded by WarpSpeed. Could you please explain a bit about the practicality of this method?

I will explain the problem as follows for those who are not clear about the problem and need some specific things. Thanks itsomked for your interest and question

1.    Accuracy – the set up is not necessary to be very accurate. There is a tolerance up to 10 cm of water.
2.    The tank doesn’t have specified control valve to measure. It has some porous side and bottom parts i.e. there are small openings at the bottom even below the reference point.
3.    What I want is exactly the variation of water depth in the tank with time at a certain reference level in the tank. If I get the water pressure at a certain point in the tank (net water pressure or to gether with atmospheric pressure), it is simple to get the water depth … elementary fluid mechanics for static instants ?
4.    The tank is open tank … just like a pond.
5.    Required data … time series of water level verses time for other model input.
6.    Budget …. Budget …. I would be glad if I can buy the pressure sensor under $20 as suggested by Riches.
7.    The tank is made of plastic
8.    The final data format should be in tabular form --- Time against water level in two simple columns.
9.    The time series is an input to simple water balance model which accounts the fluctuation of water level in the tank.
10.    Itsmoked I couldn’t get your last question…. About power…

RE: Cheapest way to measure water depth

My first thought was the float, with the drum, potentiometer and string as well...

is it possible to weigh the container? Don't laugh, I've seen it in 30 tonne tanks so it would be an option here!

Why not try to wires along the side of the tankwithout touching each other and the tank, but not far apart and see if the capacitance between them changes with the water level. You would still need a bit more than an amplifier to get the signal though :(

Two flowmeters, one on the input and the other on the output... depending on the flow I think you could manage some cheap flowmeters... :|



RE: Cheapest way to measure water depth

The name I have always used for that is a PRINCO probe and it helps to have a metal tank.  In your case a wire like a 300 ohm TV twinlead would be a good choice if you insulated the end of the wire with something like liquid tape and molded it into an epoxy weight.   This would be the timing cap of a 555 timer.  Then you measure frequency or convert frequency to DC volts.  I think this is beyond what you want to get into unless you can find an old ALBIA DM-8 capacitance module on ebay, this had a DC out.

Now really, what is your budget.  I hope you are not wasting our time  on a $20 budget.

RE: Cheapest way to measure water depth

Practicality of the method ?

It could not be simpler.  

If your PC has a games port, the potentiometer could quite likely be wired straight to the connector. Just write a simple program in Basic to read the games port, scale the data to suitable units, and print data plus time at the required measurement intervals to the screen, or printer.

A very few dollars and an afternoon, and several cups of coffee should have it working.

Rather primitive, but entirely practical.

RE: Cheapest way to measure water depth

Hiya-

Weeellll, although the game port *MIGHT* work, when I played with it a number of years ago, I was kind of dismayed as to how far the drift was on the one that I played with. It might be worth a shot though.

Here's a link that might help explain the process.  Of course you will have to replace the "lab"
equipment with some of the cheaper methods mentioned here.

Hope that this link helps. You might have to paste it together:

http://ceeserver.cee.cornell.edu/eac20/cee331/Assignments/CEE331Lab1_06.pdf#search=%22bubbler%20depth%22

It should give you most of the information that you need.  A good insturmentation amp is also required to get the output of the transducer to a "useable" level for data logging.

There is a pretty good writeup of insturmentation amps at microchip.com, however a quick google search might be better.

Hope that this helps!

 Cheers,

   Rich S.

RE: Cheapest way to measure water depth

For the data acquisition?

Try
www.dataq.com

DI-194RS - serial starter kit 4 x 10 bit, +/- 10V, <240hz sampling rate with software and cable for $25

DI-148U - USB starter kit with 4 x 10 bit, +/- 10V, <240hz sampling rate with software and cable for $50

DI-148U-SP - same as above but with 2 x pot inputs.


OR

www.measurementcomputing.com

USB analog I/O modules from $110
modules with others like 4-20mA from $200

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