Sealing Pressure Sensor to Otterbox

pressure-proofing
mechanical
water-proofing

#1

Hi all,

This is not specific to openROV, but I hope that you don’t mind helping me out anyway.

I am working on an engineering design project as a part of school and I need to seal my pressure sensor (https://www.sparkfun.com/products/12909) to the outside of my waterproof housing, which is currently an Otterbox 3000 case (https://www.adafruit.com/products/339).

This Otterbox case will be used for the initial prototyping and testing, then a smaller waterproof housing will be obtained based on the size of our final PCB and components. I’m estimating that it will end up being around the size of a GoPro housing.

The Otterbox case is rated to 100 feet. I’m hoping for a minimum depth rating of 20 feet once the pressure sensor is sealed to the outside. Can anyone offer some tips on the best way to go about accomplishing this?

Thanks in advance,
Blake


#2

@blakecarmichael,
I would recommend sealing your pressure sensor with epoxy like the way the OROV IMU Module is sealed into its acrylic case.
Regards,
TCIII AVD


#3

Thanks for your input,
I had been looking at that tutorial, but wasn’t entirely clear on how it would translate to the Otterbox. So I would obtain an acrylic case, seal the sensor breakout board inside with epoxy up until the rim of the actual sensor, and then drill a small hole for the wires to run from the acrylic case to the inside of the Otterbox? And seal that with epoxy somehow? That last part is where I get lost.

This is the epoxy putty I have: http://www.jbweld.com/products/plasticweld-epoxy-putty
I have the applicator gun as well


#4

@blakecarmichael,
After you get the pressure sensor potted in its own case, you could twist the wires together to form a cable and use a BR cable penetrator to provide a leak proof seal for the entry of the cable/wires into the Otterbox.
In regards to the epoxy putty, I would use an epoxy like the 2 ton Epoxy that is more free flowing to ensure that it covers the pressure sensor with no air gaps.
Regards,
TCIII AVD


#5

Ah, that makes much more sense now. Great, thank you. And do I need to worry about the type of wire that I use? Like is the insulation on those IMU wires anything special in regards to depth rating?


#6

@blakecarmichael,
I would use a quality 24 - 22 gauge wire similar to what OROV uses in their wire harness.
Regards,
TCIII AVD


#7

One more question: any idea on where I could have an acrylic case like that custom made to fit my sensor?

Thanks so much.


#8

@blakecarmichael,
I use pololu.com laser cutting services for acrylic cutting. I think that their minimum charge is $25 and you have to provide the laser templates.
You might be able to take an appropriately sized piece of solid acrylic to a local machine shop and have them rout a cavity it that will fit the Pressure Sensor.
Regards,
TCIII AVD


#9

I really wish I had known about this depth sensor before!


#10

@blakecarmichael,
I have one on my BlueROV2/BlueESC ROV and it is pretty accurate.
If you ever plan to use the Baro 30 with an Arduino, make sure you have a level shifter for the I2C Data and Clock lines as they are 3.3 vdc.
Regards,
TCIII AVD


#11

On industrial ROVs one does not usually trust the wire insulation to block the seawater. When the wire is potted into the penetrator you strip a little of the insulation so the potting can reliably bond to the copper conductor. This is easier with solid conductor wire. If you use stranded wire then bend the wire so it expands into a tiny birdcage shape so the potting can get between the strands.