[PSUBS-MAILIST] Depth Gage

[Alec Smyth via Personal_Submersibles]

Coincidentally I just spent yesterday afternoon selecting one of those. I
would normally prefer an analog gauge because I try to minimize electronics
to maximize reliability. However, on a 1,000 foot sub the needle would
barely move on shallower dives, so digital display is the only way to go.
The accuracy of these instruments is measured as a percent of full scale,
and a cheap one is accurate to 1% FS. For a thousand foot sub, that means
the smallest depth change it could measure is 10 feet - not good! Well, let
me rephrase that. I'm fine knowing my depth to within 10 feet, but what I
really want to know if whether my depth is increasing or decreasing, and
I'd like to know that before I've traveled 10 feet.

I settled on the Dwyer DPG-100, because it has this:

- 0.25% FS accuracy
- Displays pressure directly in feet of water
- Wetted elements are 316 SS
- IP66 enclosure (waterproof to "hose-down" standard)
- Lighted display
- Battery powered, so no need to wire it into the sub power (battery life
2000 hrs)
- Reasonably priced ($185)

It also records the max depth, hardly a necessity but cool for unmanned
depth tests. For testing my K250 I just strapped a dive computer outside,
but that wouldn't work for a test to over 1,000 feet.

Here is a link: https://www.dwyer-inst.com/PDF_files/A_34.pdf

If you want to go the Arduino or PLC route with a touch screen and all
that, you can step up to the Dwyer DPG-200 because it transmits a process
signal. The nice thing compared to the normal pressure transducers is if
your Arduino, PLC, or display screen failed, you could still see the depth
directly on the gauge. The DPG-200 also has high and low programmable
alarms with NC and NO switches, so you could use it for example to
automatically turn on your scrubber when going past ten feet, or to wake
you up with a klaxon if you are going past your max depth.   However, it
has cables coming out the back that make it a little less compact, and it
needs an external power feed. Dwyer also offers low-cost screens that you
can plug the DPG-200 depth gauge into directly without any processor.

https://www.dwyer-inst.com/PDF_files/A34A_low.pdf


I opted for the DPG-100 because my focus is on simplicity, but depending on
your priorities one or the other of these two should make a good instrument.



Best,

Alec



On Sun, Sep 13, 2015 at 8:56 PM, Jon Wallace via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

>
> SSI technologies P51 family, but Honeywell MLH500PGL01G
> <http://media.digikey.com/Photos/Honeywell%20Micro%20&%20Precision%20Sensors/MLH500PGL01G.jpg>
> is about the same price and has better accuracy.  I use combination of
> arduino, raspberry pi, and processing for my project.  See
> http://www.subdb.info/cgi/database/showvessel/albums/index.cgi?A=1320788990&B=1439139327&C=&D=Submarine%20Environment%20Monitor%20Software
>
> Jon
>
> On 9/13/2015 7:35 PM, Christopher Cave via Personal_Submersibles wrote:
>
> I'm looking to buy an electronic depth gauge. Any suggestions for a brand,
> software etc...
>
> Thanks,
> Christopher
>
>
>
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