[Adomas Mazeikis]

Hi,
I`m trying to find a low cost pressure sensor/transducer from
underwater use (water level measurement), but I`m stuck. I`ve been
searching all over search engines, component suppliers, but there are
two types of results: costs too much or specifications are out of
range (to be more specific I`m trying to find something for a
submersible water level measurement probe, it may be a differential
pressure sensor/transducer but it should be able to measure 0-10 bars
prefferably, and the accuracy should be 10mm of water or 1milibar).
Can anybody throw some suggestions where or what to search?

Maybe someone already has done some kind of project with water level
measurement. If so I`d be really grateful for help.
Buying those already made water level sensors needs a lot of money,
and as a student I don`t have $ to throw away.

Thank You

 

[Stanislaw Flatto]

Hi,
I`m trying to find a low cost pressure sensor/transducer from
underwater use (water level measurement), but I`m stuck. I`ve been
searching all over search engines, component suppliers, but there are
two types of results: costs too much or specifications are out of
range (to be more specific I`m trying to find something for a
submersible water level measurement probe, it may be a differential
pressure sensor/transducer but it should be able to measure 0-10 bars
prefferably, and the accuracy should be 10mm of water or 1milibar).
Can anybody throw some suggestions where or what to search?

Maybe someone already has done some kind of project with water level
measurement. If so I`d be really grateful for help.
Buying those already made water level sensors needs a lot of money,
and as a student I don`t have $ to throw away.

Thank You

Hi!
Lets be real. Worked with transducers ~25 years so what you want,
although possible, is VERY difficult to arrange. Hence the prices.
You define a range of 0-10bars (~ 10,000mm of water) with accuracy of
10mm, so you are on 0.1% measurable, repetitive level.
Q. Do you have equipment to simulate those conditions for calibration
purposes?
Just a note, for this accuracy you need to take into consideration
the barometric pressure at time of record, and it better be precise!
So lets be real: Use overlapping ranges of transducers with ~1%
accuracy. 10.000mm; 3000mm; 1000mm; 300mm and so on. It will be much
more real.
BTW, anything happened to proper glass tube and tape measure?
Unconvenient, you also need a ladder but doable.

Good luck.

Stanislaw.

 

[Sjouke Burry]

Hi,
I`m trying to find a low cost pressure sensor/transducer from
underwater use (water level measurement), but I`m stuck. I`ve been
searching all over search engines, component suppliers, but there are
two types of results: costs too much or specifications are out of
range (to be more specific I`m trying to find something for a
submersible water level measurement probe, it may be a differential
pressure sensor/transducer but it should be able to measure 0-10 bars
prefferably, and the accuracy should be 10mm of water or 1milibar).
Can anybody throw some suggestions where or what to search?

Maybe someone already has done some kind of project with water level
measurement. If so I`d be really grateful for help.
Buying those already made water level sensors needs a lot of money,
and as a student I don`t have $ to throw away.

Thank You

A cheap solution with a resolution of 1 in 10000 ?????????
You better start saving money, because at that resolution
you wil need a LOT of money.
If you want to keep it cheap and skip some of that accuracy,
make a closed box able to withstand your 10 bars, and use
a plate inside near a slightly flexible side of the box,
use it in an oscillator, and measure the frequency change.
If you succeed, you have just made a capacitive pressure sensor.
Solution 2:
fill a pipe with a resistor chain,and reed relays to short the chain
to ground at that place, then float a magnet outside the pipe,
such that at least two reeds switch when the magnet is near.
For protection you can fill up the pipe with tar, epoxy ,etc.
This gives about 1 inch resolution,and is rather cheap.
Solution 3:
Buy a springloaded 10 turn potentiometer,and attatch a wire and float
to that.
The accurate ones are expensive, and at ten bar you have a level
change of 100 meters (100+ YARDS).

 

[David L. Jones]

Hi,
I`m trying to find a low cost pressure sensor/transducer from
underwater use (water level measurement), but I`m stuck. I`ve been
searching all over search engines, component suppliers, but there are
two types of results: costs too much or specifications are out of
range (to be more specific I`m trying to find something for a
submersible water level measurement probe, it may be a differential
pressure sensor/transducer but it should be able to measure 0-10 bars
prefferably, and the accuracy should be 10mm of water or 1milibar).
Can anybody throw some suggestions where or what to search?

Maybe someone already has done some kind of project with water level
measurement. If so I`d be really grateful for help.
Buying those already made water level sensors needs a lot of money,
and as a student I don`t have $ to throw away.

Thank You

10mm ain't going to be easy.

The problem with cheap pressure sensors is that they may not be
temperature compensated, and that's bad news, especially if you are
trying to achieve that sort of accuracy. To compensate a cheap
pressure sensor can take a lot more effort than buying one that is
already compensated - been there, done that, not easy.

I just installed a water level gauge in my rainwater tank, it uses a
float on a string with a dial, works a treat. What is it you are
really trying to do here?

Dave.

 

[Adomas Mazeikis]

Lets be real. Worked with transducers ~25 years so what you want,
although possible, is VERY difficult to arrange. Hence the prices.
You define a range of 0-10bars (~ 10,000mm of water) with accuracy of
10mm, so you are on 0.1% measurable, repetitive level.

Well You see there`s a little problem with sensors/transducers which
are capable to handle less than 5 bars. That problem is vandalism. I
want to throw submersible water level data logger into the lake and
forget about it for 6 months. Then I`m going to visit the site, get
the data, change the battery and throw it to the depth again. If the
data logger is somewhere in shallow water or near the coast line it
may be stolen. So the solution is to keep it in quite deep place of
the lake.
Now I see that the bigger problem is to get such sensors/transducers
which are needed for such application. So I`m thinking that maybe it
is better that one or two data loggers are stolen than all of them are
expensive and hard to find in such deep parts of lakes.

Q. Do you have equipment to simulate those conditions for calibration
purposes?

Actually yes. I have lots of stuff and very good conditions for
creating, calibrating and using such data loggers but the one and only
thing is money. I must use my own money and as I mentioned I`m a
student so I don`t have lots of it.

Just a note, for this accuracy you need to take into consideration
the barometric pressure at time of record, and it better be precise!

The barometric pressure will be taken from nearby meteorological
stations+short term meteorological models.

So lets be real: Use overlapping ranges of transducers with ~1%
accuracy. 10.000mm; 3000mm; 1000mm; 300mm and so on. It will be much
more real.

I think that`s what I`m going to do...I mean thanks for solution
But maybe anyone could tell me some exact transducer model which
could be good enough for, let`s say, 10 or 3 m?

BTW, anything happened to proper glass tube and tape measure?
Unconvenient, you also need a ladder but doable.

The lake is 40-50km away from my native town, so going there everyday
takes lots of time and fuel
People living nearby the lake are not helping with this task.

Good luck.

Thank You

 

[Adomas Mazeikis]

A cheap solution with a resolution of 1 in 10000 ?????????

I know, I know. It sounds like mad science or stupid student, but I
was still hoping that there are such good stuff and it doesn`t need
lots of money wasted.

You better start saving money, because at that resolution
you wil need a LOT of money.
If you want to keep it cheap and skip some of that accuracy,
make a closed box able to withstand your 10 bars, and use
a plate inside near a slightly flexible side of the box,
use it in an oscillator, and measure the frequency change.
If you succeed, you have just made a capacitive pressure sensor.

Thank You. This solution sounds very interesting and I think I`ll try
this as an experiment next semester. Thanks again for such a good
idea.

Solution 2:
fill a pipe with a resistor chain,and reed relays to short the chain
to ground at that place, then float a magnet outside the pipe,
such that at least two reeds switch when the magnet is near.
For protection you can fill up the pipe with tar, epoxy ,etc.
This gives about 1 inch resolution,and is rather cheap.

Hm...for short time level measurements this would be nice enough.

Solution 3:
Buy a springloaded 10 turn potentiometer,and attatch a wire and float
to that.
The accurate ones are expensive, and at ten bar you have a level
change of 100 meters (100+ YARDS).

This solution is good too for shallow lakes. I think I`ll try this
when I`ll have some stuff to do in little shallow lakes or ponds.

 

[Adomas Mazeikis]

10mm ain't going to be easy.

Yes. Other replyers already opened my eyes and now I know that 10mm
with 10bars is practically impossible with cheap sensors.

The problem with cheap pressure sensors is that they may not be
temperature compensated, and that's bad news, especially if you are
trying to achieve that sort of accuracy. To compensate a cheap
pressure sensor can take a lot more effort than buying one that is
already compensated - been there, done that, not easy.

Well. Temperature is not the problem as far as in more thant 10m depth
of lakes it is quite stable.

I just installed a water level gauge in my rainwater tank, it uses a
float on a string with a dial, works a treat.

If the amplitude of measurements would be less than it is now (1,5m,
because of some heavy rain 200mm/24hours!!!) and there would be no
threat of vandalism, this would be the perfect solution, but now it`s
just useless for this application.

What is it you are really trying to do here?

I`m trying to create a submersible water level logger for local lake
level recording. And some lake levels are fluctuating 1,5m while
others are just 5-15mm.

 

[Rich Grise]

Well You see there`s a little problem with sensors/transducers which
are capable to handle less than 5 bars. That problem is vandalism. I
want to throw submersible water level data logger into the lake and
forget about it for 6 months. Then I`m going to visit the site, get
the data, change the battery and throw it to the depth again. If the
data logger is somewhere in shallow water or near the coast line it
may be stolen. So the solution is to keep it in quite deep place of
the lake.
Now I see that the bigger problem is to get such sensors/transducers
which are needed for such application. So I`m thinking that maybe it
is better that one or two data loggers are stolen than all of them are
expensive and hard to find in such deep parts of lakes.

Put some ballast in your thing so that it stays upright, and put
a waterproof ultrasonic sensor in the top, then just ping the surface.

Your signal will be very noisy (from waves and chop and such), but
shouldn't be hard to average.

Good Luck!
Rich

 

[David L. Jones]

Yes. Other replyers already opened my eyes and now I know that 10mm
with 10bars is practically impossible with cheap sensors.


Well. Temperature is not the problem as far as in more thant 10m depth
of lakes it is quite stable.


If the amplitude of measurements would be less than it is now (1,5m,
because of some heavy rain 200mm/24hours!!!) and there would be no
threat of vandalism, this would be the perfect solution, but now it`s
just useless for this application.


I`m trying to create a submersible water level logger for local lake
level recording. And some lake levels are fluctuating 1,5m while
others are just 5-15mm.

Where do you plan on putting the sensor?
If you put it near the edge of the lake you could get away with a
smaller range pressure sensor (say 1bar) and sit it in <10m of water
to measure the relative difference. That way it would be easier to get
the resolution you need.
Then it's just a simple microcontroller to log the data, just make
sure you average it to take out the fluctuations though.

You can always do the same thing with a rod and some sensors attached
at even spacing, just keep the rain off. Silicon Chip had a design the
other month for a DIY tank water level indicator.

Dave.

 

[Peter]

Try Electrosense Technologies at

http://www.electrosense.com.au

They have a differential pressure water level data logger for under US$250.
Comes in a range of depths. 0-3 meters has precision of 3mm

Pete