Barometric pressure sensor inside a non-conductive liquid..

[the_paradox]

Hello guys and gals !

I am doing some experimentation with Bosch BMP085 pressure and temp sensor. If my idea succeeds I have plans for some product ideas to go ahead with. I know that BMP05 has been discontinued. I can use BMP180.

My question is, can i use BMP085 or any other barometric pressure sensor inside a non-conductive liquid medium to measure the pressure at a depth?

Because, these are some cheaply available sensors. The ones which are waterproof are very costly.

I thought about isolating the sensor with an air tight box so that as the fluid pressure changes at some depth the air pressure in the air tight box also changes and I can read those pressure changes. But the problem with this idea is that air is compressible. And the sensor reading of pressure will not be linearly related with liquid pressure.

So, I am thinking, if it's possible to fill that air tight box with a non conductive liquid, i will be able to achieve that linearity.

All inputs are welcome. Even alternative ideas, different kind of sensors in the same or lesser price tag, or any other opinions...

Thanks in advance

Prasad Bhat

 

[dick_freebird]

You might look at fuel pressure senders like Kavlico,
they read absolute pressure and at least one end is
meant to be wet; the other (electrical connector)
might be OK with a good potting.

A mechanically hard tube filled with incompressible
fluid, with a diaphragm head at the far end might
do the job, you might have to cal-map it yourself
to take out the residual tube and fluid and volume-
ratio error terms but this ought to be a one time
exercise.

 

[Warpspeed]

Depending on the pressure, you might be able to just fit the absolute pressure sensor inside an air filled balloon or condom, then bind the opening to the cable.

If the pressure is more extreme, the same idea will work with something more robust like a section of bicycle inner tube filled with some light oil.

The more usual way to measure hydrostatic pressure at depth is to lower a hose to that depth, then raise the air pressure in the hose until the submerged end just bubbles. You can then measure the air pressure in the hose above the surface, and keep the sensor well above the fluid level and completely dry.

This idea is very commonly used to measure water level in dams, storm water drains and sewers, and it works very well with extremely dirty toxic or aggressive fluids.

 

[the_paradox]

Thanks for your response @dick_freebird.

You might look at fuel pressure senders like Kavlico,
they read absolute pressure and at least one end is
meant to be wet; the other (electrical connector)
might be OK with a good potting.

But as I mentioned in my question descriptions, liquid pressure sensors like Kavlico are very costly. There is like a 50-60$ difference between BMP180 and Kavlico. That is why I want to use Barometric pressure sensors.

A mechanically hard tube filled with incompressible
fluid, with a diaphragm head at the far end might
do the job, you might have to cal-map it yourself
to take out the residual tube and fluid and volume-
ratio error terms but this ought to be a one time
exercise.

I could not understand whether you are talking for barometric pressure sensor or for Kavlico.

 

[the_paradox]

Depending on the pressure, you might be able to just fit the absolute pressure sensor inside an air filled balloon or condom, then bind the opening to the cable.

If the pressure is more extreme, the same idea will work with something more robust like a section of bicycle inner tube filled with some light oil.

The more usual way to measure hydrostatic pressure at depth is to lower a hose to that depth, then raise the air pressure in the hose until the submerged end just bubbles. You can then measure the air pressure in the hose above the surface, and keep the sensor well above the fluid level and completely dry.

This idea is very commonly used to measure water level in dams, storm water drains and sewers, and it works very well with extremely dirty toxic or aggressive fluids.

Your inputs are very insightful Tony. Thank you.

If the pressure sensor like BMP180 is submerged in non conductive oil, will it still work?

If I use the technique of putting a hose at certain depth, shouldn't that hose be small to hold the air in and water out?

Thanks again for your response

Prasad Bhat