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Home > Archive > Alternative Power sources > October 2005 > Water pressure (depth) sensors?
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Water pressure (depth) sensors?
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| William P. N. Smith 2005-10-14, 2:21 pm |
| I'm looking for a submersible water pressure sensor for measuring the
depth of the water in a concrete cistern. I'm looking for a presure
range of something like 0-5PSI. I've found some $500 ones with 0.1%
FSO repeatability and linearity, but there must be something cheap out
there...
Tanks [sic] for any thoughts!
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| Derek Broughton 2005-10-14, 3:21 pm |
| William P. N. Smith <> wrote:
> I'm looking for a submersible water pressure sensor for measuring the
> depth of the water in a concrete cistern. I'm looking for a presure
> range of something like 0-5PSI. I've found some $500 ones with 0.1%
> FSO repeatability and linearity, but there must be something cheap out
> there...
>
A quick google for "pressure transducer waterproof" found
http://www.jumousa.com/xcart/customer/home.php?cat=283
which has sensors as low as $75
Caution: I don't know _anything_ about this stuff - I just took it as a
Google challenge :-) I couldn't begin to guess whether this is what you're
looking for!
--
derek
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| William P. N. Smith 2005-10-14, 5:21 pm |
| Derek Broughton <news@pointerstop.ca> wrote:
>A quick google for "pressure transducer waterproof" found
Thanks, every once in a while I need someone to whack me over the head
with a "Google Is Your Friend" reminder.
Turns out "submersible pressure sensor" isn't a bad search term. I'd
like to hear from anyone with experience with a particular product, if
there's anyone out there...
Thanks!
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| On Fri, 14 Oct 2005 12:35:53 -0400, William P. N. Smith <> wrote:
>I'm looking for a submersible water pressure sensor for measuring the
>depth of the water in a concrete cistern. I'm looking for a presure
>range of something like 0-5PSI. I've found some $500 ones with 0.1%
>FSO repeatability and linearity, but there must be something cheap out
>there...
>
>Tanks [sic] for any thoughts!
Not a sensor but... I'm going to use 4 Crydom RSF85Y100R switches to
indicate level and automate filling of a 6 foot tall tank. They'll be
mounted on Tees in a length of PVC pipe. The system uses a timer
alone now (with occasional manual intervention) so that pumping takes
place in the middle of the day (or at multiple specific times when we
we're watering cattle but don't want the well over-pumped). I'll keep
the timer but add automatic shutoff when the tank is full.
http://www.crydom.com//userResource...rydom_rsf80.pdf
http://www.galco.com/scripts/cgiip....RSF83Y100R-CRDM
Wayne
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| Nick Hull 2005-10-15, 12:21 am |
| In article <sanvk1p3u932ge3u85ju6v9vcrvllhm8fo@4ax.com>,
William P. N. Smith <> wrote:
> I'm looking for a submersible water pressure sensor for measuring the
> depth of the water in a concrete cistern. I'm looking for a presure
> range of something like 0-5PSI. I've found some $500 ones with 0.1%
> FSO repeatability and linearity, but there must be something cheap out
> there...
For cheap, put a tube into the tank and a pressure gauge (or U tube)
outside the tank. Blow into the tube, excess pressure will bubble out
the bottom, read the gauge.
--
Free men own guns, slaves don't
www.geocities.com/CapitolHill/5357/
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Put a electrode on the bottom of the tank...float another electrode
on a float....measure the resistance between them....can give you
approximate depth....resistance will increase with depth....
thank you for listening to my thoughts......sno
Nick Hull wrote:
>
> In article <sanvk1p3u932ge3u85ju6v9vcrvllhm8fo@4ax.com>,
> William P. N. Smith <> wrote:
>
>
> For cheap, put a tube into the tank and a pressure gauge (or U tube)
> outside the tank. Blow into the tube, excess pressure will bubble out
> the bottom, read the gauge.
>
> --
> Free men own guns, slaves don't
> www.geocities.com/CapitolHill/5357/
--
Seen it all, done it all, can't remember most of it
This tag line is generated by:
SLTG (Silly Little Tag Generator)
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| Gordon Richmond 2005-10-15, 4:21 am |
| There is a level sensor system that is used on the mud tanks of
drilling rigs. Consists of a spherical float, with a sleeved hole down
its axis, and a magnet is incorporated with the sleeve.
The float rides on a stainless-steel tubular column, which has within
it a long network of resistors shunted by reed switches. Basically, it
is wired as a voltage divider whose output is proportional to the
location of the float on the column. Practically indestructible.
I think all the current ones work on the 4-20 mA standard for
instrumentation.
This is something that one could easily duplicate at home. I used to
know the name of these sensors, but it slips my mind right now.
Alternatively, you might want to have a look at the water level sensor
used in automatic washing machines. IIRC, they contain a diaphragm and
a microswitch, and are adjustable to various set-points. If have ready
access to a dump or appliance graveyard, you could scrounge a bunch of
these, and work with them.
Gordon Richmond
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| Gordon Richmond 2005-10-15, 8:21 am |
| Follow-up.
I used to know these things as deLaval pit probes, but could not find
them on Google under that name. They are now called Gem sensors.
Here's a link: <http://www.oiusa.com/pitProbe.aspx>
I've also used an ultrasonic sensor, similar to the one pictured, and
they're very easy to set up and use.
For that matter, I remember using pressure transducers mounted in a
port near the bottom of a 400-barrel tank to gauge the volume based on
the hydrostatic pressure at the bung.
These commercial sensors, I expect, will pretty well all use the 4-20
mA current loop transmission protocol, if they aren't fully digital.
FWIW, I have a concrete rainwater cistern at my home, and I bought a
simple mechanical float switch to kick on the pump when it fills to
the point of overflowing. Cost about $35, and consists of a
lemon-shaped plastic ball float, with a ball bearing inside it. The
electric cable exits one end. There is a switch inside the float at
the cable end. If the ball floats cable end down, the ball closes the
switch; if it floats or hangs cable end up, the switch opens. There's
a certain amount of dead-band, which is a good thing.
You should be able to get such a switch at any retailer that sells
sump pumps. Probably the simplest solution for cisterns. Depending one
how one installs it, and what freedom of movement is provided, you can
use it to kick on a pump to partly empty the cistern if it becomes too
full (my application), or use it to shut down a pump if the cistern
level falls too low.
Hope this helps,
Gordon Richmond
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| In article <sanvk1p3u932ge3u85ju6v9vcrvllhm8fo@4ax.com>,
William P. N. Smith <> wrote:
> I'm looking for a submersible water pressure sensor for measuring the
> depth of the water in a concrete cistern. I'm looking for a presure
> range of something like 0-5PSI. I've found some $500 ones with 0.1%
> FSO repeatability and linearity, but there must be something cheap out
> there...
>
> Tanks [sic] for any thoughts!
Hey Bill, Have you looked at the Motorola solid state pressure sensers?
I have used these in air water and even some chemicals. They are fairly
cheap and seem to be above average for ruggedness.
Me
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| William P. N. Smith 2005-10-15, 3:21 pm |
| Me <Me@shadow.orgs> wrote:
>Hey Bill, Have you looked at the Motorola solid state pressure sensers?
Yeah, my main problem is that the sensors have to be submersible
(there are no holes in the bottom of the cistern, for obvious
reasons), and have to be compensated for atmospheric pressure, as an
inch of mercury is about a foot of water depth...
Looks like it's not as trivial as it seems.
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| Loren Amelang 2005-10-15, 5:21 pm |
| On Sat, 15 Oct 2005 13:36:42 -0400, William P. N. Smith <> wrote:
>Yeah, my main problem is that the sensors have to be submersible
>(there are no holes in the bottom of the cistern, for obvious
>reasons), and have to be compensated for atmospheric pressure, as an
>inch of mercury is about a foot of water depth...
>
>Looks like it's not as trivial as it seems.
True. I searched very hard for an affordable solution. A submersible
pressure transducer, as you say, must be vented all the way up the
cable. Lowest price I found was around $500, but I needed 150' of the
vented cable. For your probably shorter cable the price might be half
that. Ultrasonic sensors are cool, but again the price bottomed at
close to $500, and the range didn't include my 150'.
I ended up with a tube to the bottom of the well (1/4" drip tubing), a
tiny air compressor, pressure tank and differential switch, and a
carefully adjusted needle valve to keep the tubing just barely
bubbling.
With the pressure transducer aboveground and measuring air pressure,
it can be very low cost. The first type in the chart at
<http://www.servoflo.com/fujikura/pr...ied_sensors.htm>
cost me about $20. Output is 0-5 VDC, which was perfect for my control
system, but they have a chip to convert it to 4-20 mA if you have a
long cable run or a current input.
A lot of hassle compared to dropping one cable down the well, but an
order of magnitude cheaper...
Loren
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| nospam.clare.nce@sny.der.on.ca 2005-10-16, 12:21 am |
| On Sat, 15 Oct 2005 13:36:42 -0400, William P. N. Smith <> wrote:
>Me <Me@shadow.orgs> wrote:
>
>Yeah, my main problem is that the sensors have to be submersible
>(there are no holes in the bottom of the cistern, for obvious
>reasons), and have to be compensated for atmospheric pressure, as an
>inch of mercury is about a foot of water depth...
>
>Looks like it's not as trivial as it seems.
Very trivial. The SENSOR does not need to be submerged. all you need
is a fine bore tube to the bottom of the tank with the sensor at the
top. Small bore will not allow the sealed tube to fill with water. You
want a differential pressure sensor. If you can get one with a 0-5
volt output you can put an adjustable shunt across it and connect it
to a 0-1 volt meter, with the shunt adjusted to make the meter read
full scale when full. It will then show 1/2 when half full, and be
accurate.
In a cistern, likely a good idea to put a pickup filter on the bottom
of the tube to keep it from being blocked by a bit of dirt. Use the
pickup filter from a chainsaw fuel line. About $2 each.
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| Bill Kaszeta / Photovoltaic Resources 2005-10-16, 1:21 am |
| On Sat, 15 Oct 2005 13:36:42 -0400, William P. N. Smith <> wrote:
>Me <Me@shadow.orgs> wrote:
>
>Yeah, my main problem is that the sensors have to be submersible
>(there are no holes in the bottom of the cistern, for obvious
>reasons), and have to be compensated for atmospheric pressure, as an
>inch of mercury is about a foot of water depth...
>
>Looks like it's not as trivial as it seems.
I solved a similar problem measuring fuel in a dual-wall diesel tank that
does not have outlets in the bottom, only the top.
I used a tube a little longer than 3 times the height of the tank, forming it
into a 'U' over the top, placing a 'T' on the outside end, placing a
differential pressure sensor from one side of the 'T' (air pressure on
the other side) and using the remaining tubing to run from the 'T'
to above the top of the tank. Then a little suction on the top can
form a siphon in the 'U' and up to the level of the fuel. The sensor
sees the same pressure it would see if inside the tank at the same
level. Minor bubbles forming in the tubing do not affect the reading.
You can use clear plastic tubing for water, but will need a sensor
designed for water. With the right sensor you can resolve 1/2" depth.
If you only need a switch action, there are wire probes that work
well. Most well supply companies have these.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
bill@pvri-removethis.biz
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| Peter K 2005-10-16, 8:21 am |
| Try
http://www.electrosense.com.au
This is a low cost wireless water level system specifically designed for
water tanks. Minimal maintenance and 1 mm resolution.
Regards
Pete
<William P. N. Smith> wrote in message
news:sanvk1p3u932ge3u85ju6v9vcrvllhm8fo@4ax.com...
> I'm looking for a submersible water pressure sensor for measuring the
> depth of the water in a concrete cistern. I'm looking for a presure
> range of something like 0-5PSI. I've found some $500 ones with 0.1%
> FSO repeatability and linearity, but there must be something cheap out
> there...
>
> Tanks [sic] for any thoughts!
| |
| daestrom 2005-10-16, 11:21 am |
|
<William P. N. Smith> wrote in message
news:4df2l150a8hpq184ak944dubbbg3c9tvso@4ax.com...
> Me <Me@shadow.orgs> wrote:
>
> Yeah, my main problem is that the sensors have to be submersible
> (there are no holes in the bottom of the cistern, for obvious
> reasons), and have to be compensated for atmospheric pressure, as an
> inch of mercury is about a foot of water depth...
>
> Looks like it's not as trivial as it seems.
If you can't submerge the sensor, the easiest way is to use a 'dip tube'
type of setup. A small plastic tube with a weight on one end to hold it
down in the bottom of your tank. On the other end, a 'tee' with a gage
pressure sensor on one leg, and a source of very low pressure air on the
other. Trouble with this is you must adjust the air flow to *very* low
flow, so just a bubble every second or two percolates up from the bottom end
of the dip tube.
If you want continuous measurements, you need continuous air supply. If you
just want to check the level once/twice a day, a tiny hand pump can be used.
Pump the air until you're sure the line is cleared, then stop pumping.
After you stop, the pressure in the line will stabilize and you can take a
reading. For intermittent use, you can get just a direct-reading pressure
gage of the right range. To help stabilize the readings, you can attach a
sort of 'diving bell' to the lower end (think of an inverted drinking cup).
This will provide a larger volume of air that has to leak off before
affecting the reading very much. Of course, it takes more weight to hold
such an air volume under water. Maybe permanently attach it on the inside
wall while the cistern is empty for maintenance.
Using a 'gage' pressure sensor means it will sense the difference between
the sensing tap and the atmosphere around it, thus compensating for changes
in the weather. If you can only find 'absolute' instruments, then you must
get two and use one to measure the atmospheric pressure, and one to measure
the pressure in the sensing 'dip tube'. Then the pressure difference is
caused by the depth and density of the liquid being measured.
Along with the various differential pressure schemes, there is also the use
of a float pulling up/down on a string/wire and looping the wire around a
form of revolution counter (these can be direct reading, or electronic).
Also the float with a magnet riding up/down a tube with a series of
reed-switches. Or, an insulated wire inside a free-flooding tube to measure
the different capacitance constant between air and water (the insulated wire
forms one plate of a capacitor, the tube the other plate, with air/water as
the dielectric). Although a bit high-tech, I've also seen the ultra-sonic
range finders such as some cameras used to have to measure the distance from
the top to the surface of the water.
Using two uninsulated wires and measuring the relative conductivity can be
pretty impractical if you don't know the variability of the water's purity
(although a separate 'reference cell' in the same tank could be used in some
form of bridge). Best to use a very low voltage AC in such a setup to
minimize glavonic-like corrosion of one side.
The capacitance and resistivity probes can have calibration issues if there
is any growth of 'organics'. And obviously, floats sometime sink, and
tubing sometimes can clog. They all have various advantages/disadvantages.
As you can see, there are *lots* of ways to measure the depth of the water
besides differential pressure.
daestrom
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| RF Dude 2005-10-16, 2:21 pm |
| You can convert any 4-20 mA sensor to 1-5V indication with a 250 ohm
resistor, or set up a resistor circuit with a regulated power supply of your
choice to give you a suitable range (example, 4.0V = 4000 liters). There
are shareware programs out there where you can create a replacement meter
scale and thus you have calibrated a 5V full scale meter movement to any
range you want.
One other overlooked and nearly free solution is in your washing machine. A
pressure switch in the washing machine control panel turns off your water
fill solenoid in the laundry tub. When you change the amount of water you
want in the tub you are actually changing the spring pressure on the
diaphram pressure switch. Find scrapped washing machines and you have a
free source of diaphram pressure switches. Of course, this is only on/off,
not a range.
Good luck.
| |
|
| On Fri, 14 Oct 2005 12:35:53 -0400, wrote:
> I'm looking for a submersible water pressure sensor for measuring the
> depth of the water in a concrete cistern. I'm looking for a presure
> range of something like 0-5PSI. I've found some $500 ones with 0.1%
> FSO repeatability and linearity, but there must be something cheap out
> there...
>
> Tanks [sic] for any thoughts!
I have seen quite cheap designs for measuring fluid levels, using
ultrasonic transducers to measure distance between the top of a tank and
the fluid level.
Sorry I don't know of any cheap submersible pressure sensors.
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| quietguy 2005-10-18, 5:21 am |
| ...and I saw a circuit that used a simple pair of wires as a capacitor with
the water acting as a dialectric - that 'cap' then controlled the frequency
of an oscillator, and another chip converted frequ to voltage - very neat,
and very cheap to make
David
Jon wrote:
> On Fri, 14 Oct 2005 12:35:53 -0400, wrote:
>
>
> I have seen quite cheap designs for measuring fluid levels, using
> ultrasonic transducers to measure distance between the top of a tank and
> the fluid level.
> Sorry I don't know of any cheap submersible pressure sensors.
| |
| Solar Flare 2005-10-19, 12:21 am |
| NivoTube detectors come to mind.
"quietguy" <quietguy@REMOVE-TO-REPLYconfidential-counselling.com> wrote in
message news:4354A81F.C1F4563@REMOVE-TO-REPLYconfidential-counselling.com...
> ..and I saw a circuit that used a simple pair of wires as a capacitor with
> the water acting as a dialectric - that 'cap' then controlled the frequency
> of an oscillator, and another chip converted frequ to voltage - very neat,
> and very cheap to make
>
> David
>
> Jon wrote:
>
>
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