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Re: [PSUBS-MAILIST] Water depth sensing?

For a depth sensor you really want absolute.
The downside to using gauge pressure is that it gives you the pressure relative to the inside of the ROV (or electronics bottle). This is only a problem if you're using hull vaccume to hold the end caps in (as done on DOE vehicles).
This is simple enough to solve by implementing a means to zero the depth reading in software.
Desert Star Systems http://www.desertstar.com has something listed on their web page that might be useful, though it might be OMG expensive.
IIRC good quality pressure transmitters cost between $500 and $1000 so they might be cost competitive.
Given the choice I would use a 0-5V Absolute and interface it to Netmedia BX24. In a time crunch I've had ok experience with 0-5V gauge sensors and 4-20 mA sensors, though we only saved a two week order lead time since the pricing was the same.
The BX 24 gives you an easy way to interface an SPI or serial compass module as well. 

let me know if you need any pointers :)

mike


Warren Greenway wrote:


The only real difference is the point of reference for
the sensors. You would want an absolute sensor for
sensing depth/pressure for a sub. Gauge often means the same thing as absolute, differential will have two 
sensor inputs and read the difference between the two.
Try the datasheets for the sensor you are interested in. Usually the datasheet will have some standard interface circuits and information. Also, get TI application notes book for the MSP430...Even if you 
are
using any MCU. It has great circuits and algorithms
for reading various common sensors.

Warren.

normaly means that there will be t
--- steve <steve@kobol.worldonline.co.uk> wrote:


another question on the subject if i may.
i have heard there are three different types of
sensor available: absolute,
differential and gauge.
i have an idea what the differential type does but
what about the other two?
what should i be looking for to get a linear 0 - 5v
or 0 - 10v output i can
feed to an A to D converter?

Best Regards

Steve Bosworth
UK

----- Original Message -----
From: "Steven Mills" <cirtemoeg@juno.com>
To: <personal_submersibles@psubs.org>
Sent: Saturday, February 21, 2004 7:41 AM
Subject: Re: [PSUBS-MAILIST] Water depth sensing?




Steve, here are a few links that I recall.

http://members.cox.net/igalysh/pressure.html






http://www.parallax.com/html_pages/resources/custapps/app_underwater.asp


I have many more sources, but the case and hinge


on my laptop cracked a


few
months ago [ no video ] so I'm starting over with


the searches/sources


[and
everything else !  ]
When I come across anything significant I'll post


it.


--Steve


On Sat, 21 Feb 2004 02:16:40 -0000 "steve"
<steve@kobol.worldonline.co.uk> writes:


anything helps, thanks.
i had originally considered the low tech


approach but as the project


progresses i keep moving the boundaries.  in one


way i actually know


it
could be done visually but where is the


challenge?


steve

----- Original Message -----
From: "Al Secor" <wreckdiver@usadatanet.net>
To: <personal_submersibles@psubs.org>
Sent: Friday, February 20, 2004 12:42 PM
Subject: Re: [PSUBS-MAILIST] Water depth


sensing?




Steve,

I'm using a pressure sensor from Digikey


(www.digikey.com) for my


rebreather


controller which uses a PIC processor. Mine is


a 0-250 psi sensor


which
will


measure down to about 600 feet but you can get


them that measure


0-100
psi.


The particular sensor I'm using is a


Measurement Specialties


2000519.  It


has a .5-4.5v ratiometric output voltage and


runs on 5 vdc and a


1/4" NPT


pressure port.  The downside is they are


somewhat pricey....about


$100.00.


Hope this helps....Al

Al Secor  ARS: WA3PWX  Scuba Instructor SSI


PDIC TDI


http://www.geocities.com/SubDiverI
----- Original Message -----
From: "steve" <steve@kobol.worldonline.co.uk>
To: <personal_submersibles@psubs.org>
Sent: Friday, February 20, 2004 3:37 AM
Subject: Re: [PSUBS-MAILIST] Water depth


sensing?




Hi All

Unfortunately there is still no sign of the


Kitteridge book but


i expect


the
US / UK post offices are taking their time. 

maybe they read


everything


they


send???

As part of my ROV project i want to look at


a way of measuring


the depth


of


my vehicle.  I am toying with a Basic stamp


2 at the moment and


wondered


if


anyone had any ideas for a small (i.e.


cheap) sensor that i


could use
for


this purpose.
My design spec will only need to measure


down to 20m in fresh or


sea


water.


anybody got any useful ideas and know where


i could source one?


Best Regards

Steve Bosworth
UK
----- Original Message -----
From: "Dewey Mason" <drmason2001@yahoo.com>
To: <personal_submersibles@psubs.org>
Sent: Friday, February 20, 2004 1:50 AM
Subject: Re: [PSUBS-MAILIST] test of CO2


safety hardware - any


volunteers?




If tested well, and found to work, this


could serve as


a backup unit to a commercial device, or


even just as


a novelty, but I agree in should be looked


into. My 2


cents.

Dewey
--- Pierre Poulin <pipo305@hotmail.com>


wrote:


Erik,

I will try it. I just need some time. I


will try it


mainly for curiousity
and discution. I think that's all this


group is all


about! To get new things
developed and discussed.

Pierre Poulin





From: Erik Muller <emuller@naic.edu>
Reply-To:


personal_submersibles@psubs.org


To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] test of


CO2 safety


hardware - any volunteers?


Date: Wed, 18 Feb 2004 12:23:52 -0400

Gail,
Many of the points you made are true.


Let me


address them one at a time:


I'm wondering how accurate and useful


a device


like the one you describe


would be.
Indeed, as am I. This is why I am


calling for


people with air-tight hulls


to test the system. I am not suggesting


that it be


implemented on anyones


machine before testing its efficiency


and it is


developed.


With reliable professionally-made
devices 

=== message truncated ===


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