Pressure sensor

I want to use a pressure sensor to measure the depth of water, it will be attached to a ROV. Am i right in thinking i need an absolute pressure sensor? Also when i look at them they all come in different pressures so if i wanted one which would measure between 0-10m would i then look for a sensor that covers 14.6 psi to 29.3 psi?

An absolute (baromic) pressure sensor of course, you don't want an air tube to the surface to measure the differential pressure :slight_smile:

There are pressure sensors that are specific to measure depth under water, try to google for: submersible pressure transducer.
Or: submersible pressure transmitter
Or: submersible pressure sensor
Or: water level sensor

How big or how small may it be ? Should it be (industrial grade) accurate ?

Ok thank you. I’m not looking to spend tons on a special underwater one. I’m thinking that it doesn’t necessarily have to be a special underwater one, i could locate it on the outside and waterproof it myself with resin etc… As for how big, not sure but probably no more than 1 or 2cm squared. Its just for hobby purposes so if it can do +/- a couple of cm’s that would be ok. I’ve found this which looks like what i’m looking for:

Which HoneyWell sensor is that ?

(I'm having some computer trouble, I can't open the link on my tablet, sending an email to my main computer didn't arrive, and so on)

You could buy an 200kPa (or more) abosulute pressure sensor.
At freescale they have them. For example the MPX4200, MPXx2200 / MPX2200.
I think for 10 euros you can buy such a sensor.

Making your own submersible version for 10 meters is not easy. I like that you are confident about it, so give it a try !
I have a few flat silicon sheets of 1 and 2mm thickness. That would be my first choice. Keep as little air around the sensor as possible, but the flexible membrane (between the water and the sensor) has to be able to move inwards with the pressure.

Do you know FSR ? google for : sparkfun fsr
They are flat, and don't need air, you can stick it to the outside of the ROV and add a silicon layer on them. The accuracy might be +/- 2 meters.

I have been looking for (digital) absolute pressure sensors myself. For example the BMP180 in a version for a few hundred kPa. I would like to place a number of them in an air pressurized project, so I could calculate differential pressure and even flow. But sadly they don't seem to exist for a low price.