Water Depth Pressure Sensor?!?!

Discussion in 'Electronic Basics' started by Dan T, Jan 6, 2004.

1. Dan TGuest

Hi all, I'm planning on measuring the depth of water using some form of
pressure sensing. Does anyone out there know of any pressure sensitive
resistors that would be suitable for this, that aren't too expensive? All
the ones I find on the net are pretty OTT for what I'm trying to do.

Thanks,
Dan

2. Dan TGuest

.....or even better a device that can give a varing output voltage depending
on pressure.

3. John PopelishGuest

Digikey lists 760 different pressure sensing transducers, some of them
quite inexpensive. How deep do you need to measure?

4. Henry KolesnikGuest

you didn't mention how deep..
a couple of simple things..
washing machine water level sensors have a limited range and are cheap and
relaible!
a toilet float with a pot on an arm would work..
hank wd5jfr

5. Dan TGuest

not deep.....0 - 1 meter would be more than enough.

6. John PopelishGuest

Is the water inside a vessel, or exposed to atmosphere? Can you run
an air tube from above the water to the sensor, to give a surface
pressure reference? Remember each 2.2 feet depth of water accumulates
about 1 psi of pressure, so you need a transducer that has a full
scale pressure range of at least 1.5 psi.

Here is a 0-2 psid (pounds per square inch differential) device:

http://rocky.digikey.com/WebLib/Measurement Specialties Inc/Web Data/Model 1210.pdf

sold by Digikey for under \$30 that could be potted and submersed with
an air tube run to above the surface connected to one port, and the
other port open to the water. Of it could be outside a tank, at the
level of the bottom of the tank, with one port connected to the water,
and one vented to air. That would measure the height of the surface
above the transducer.

7. RileyesiGuest

Remember each 2.2 feet depth of water accumulates
John,

Can you give me a reference for this type of information? I need to find out
the change in pressure per depth for salt water and fresh water at different
temperatures.

Thanks loads (if you'll pardon the pun!).

Pete

8. John FieldsGuest

---
Different John, but here's a link for pure water:

http://www.muellercompany.com/test/mueller_water/water/W16_19.pdf

Salt water's a little tougher since density varies with salinity _and_
temperature, but here's a great link with a calculator!

http://ioc.unesco.org/oceanteacher/...te/Sea Water Equation of State Calculator.htm

9. erehwonGuest

Hi,
Here's what I'm using for pretty much the same thing (ie. same depths):
Motorola's MPX5100DP

It cost me £10 from Arrow Electronics

JJ

10. John PopelishGuest

http://www.mcdanielcontrols.com/pressureunits.htm

Covers pure water, but not salt water.

11. Dan TGuest

thanks for the replys guys, ...stupid question though.....how do you put one
of these devices actuatly in water????

12. erehwonGuest

Just to give you some idea: The 'package' in my case is a small plastic case
with metal connectors for the electronics side of things, and has a couple
of 'push-on' connectors for the pressure connector. So you just push some
small tubing on and take that to the place you're measuring from. (You
probably want to give the tube a few large turns so that you don't
accidently get any water up it into the sensor.)
My tubing is from the local Aquarium and fits okayish.

Out of curiosity - can I ask what you're making?

JJ

13. Dan TGuest

for part of my training for work i've got to come up with some electronic
system of measuring how much fuel is in a aircrafts fuel tank (not real,
just imaginary)......and have it shown on a display. Its all for a
competition. Once i've got a output thats proportional the the liquid level
i'm fine. We can't use floads, or arms adjusting a pot, or do anything that
involves direct contact with current and fuel.

thanks for ur help everyone,
DT