PPM-MarkIII for underwater surveys

Hi all,

Up to now, we have concentrated our efforts to make a good PPM for underground surveys and this is now accomplished with our PPM-MarkIII version.
However, we're perfectly aware of the fact that underwater surveys have an even more crucial need for a PPM instrumentdesigned and built specifically for that purpose.
Thus, with the help of a client, we have now started the design of the underwater option of our PPM-MarkIII.

What features do we need to add to the PPM-MarkIII to make it useable at sea/lake?

1. The electronic system and its external connections should be sea water splash-proof.
This is already the case for the standard control box (a NEMA box) but its standard connectors are only IP67-rated, not IP68-rated as it should be. Thus, one option is to replace the external connectors of the NEMA box with IP68-rated connectors.

2. The surveys must be GPS-supported, preferably from the GPS of the boat.
This is being designed as follows:
    a. The PPM supports a new feature: 'Journal Option' which generates one line of text on its serial line per PPM reading in parallel to its storage on a grid file on SD Card.
    b.  We have written a Windows-based PPM/GPS multiplexing program  which receives the PPM data stream from one of its COM port, receives the GPS NMEA0183 data stream from any external GPS device through another COM port, merges the two streams into one single survey line per second and stores it into a file on the laptop. As a further option, the program can also re-emit the NMEA stream to a third COM port to feed a GPS-supported GIS program to show the boat survey path on a geographical map. As the current laptops do not support any RS232 port any longer, the COM ports are simulated by small (and cheap) USB/RS232 converter boxes.

3. The sensor has to be inserted into a towing fish under a pressure-protected ccntainer.
We have found that it is not really necessary to make the complete fish as a pressure-protected ccntainer. We are designing a small container with its dimensions selected to fit our sensor coils in in-line configuration. It is built from a section of high-pressure PVC pipe (90mm outside diameter, 7mm thick walls) closed with two machined caps each with double O-rings. The cable goes through an IP68-rated connector guaranteed to support 100m depth for several hours. The sensor container just needs to be inserted inside a fish made of simple PVC pipe with a nose and fins on which the lead weights and the towing cable have to be fixed.

This is a work-in-progress which is being built as a first prototytpe. The sensor container will be depth-tested first on a deep lake here in Belgium and then, the whole system will be experimented first on the lake,then, at sea..

Any comment or remark is very welcome.

Willy
Hi,

This is two pictures of the pressure container we'll use for submarine work.

Willy

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The only 'slight' problem is that the coils should contain or be inside a proton-rich FLUID. Any grease or gel would not allow the protons to precess.
What can be done is to fill the whole container with fluid instead of using bottles. This would also help the container to support the external water pressure.
We can not use water because it takes too long polarization periods (1 to 3 seconds), thus, we use isopropylene (isopropyl alcohol)  giving a good signal after only 600msec of polarization current. This allows us to keep a sustained reading rate of one per second.
However, at this moment, we still do not have long enough experience with proton-rich fluids which would not destroy the wire's varnish in the long run.

Willy
Hi,

This is a screen dump of a replay run of the PPM-GPS mixer program.
Willy


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This is a first experimental survey in Mauritius over a known shipwreck sitting at a depth of 10meters. It is an old wooden boat but still with its cannons nearby.
The fish was flying at 1.5meter deep.
You can see the slow but large field gradients due to the variations of volcanic ground composition and then, the very recognizable double peaks made by the cannons seen by the PPM as a magnetic dipole.

This survey has been made with a separate GPS logger and the data from the PPM has been mixed with the GPS log using a PC program.
The next experiments will be made with a GPS device integrated in the control box to directly mix the PPM data and the corresponding GPS fixes during the survey session.
A PC program has been written to display the GPS track and the PPM gradient barchart in real-time on a laptop connected to the PPM as an added option.

Willy

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Hi all,

We are now in the state where we can offer a semi-finished PPM system for undewater surveys.

The only critical component to add to our existing PPM system was a pressure-protected container for the sensor coils.
We are now able to produce such a container with a professional quality. It has been thoroughly tested at sea by one of our clients.

However, it has still to be enclosed in a 'towing fish' made of a simple PVC tube with fins and tip as well as its fixing straps.
A towing cable paired to a shielded communication cable of proper length has also to be provided.

Apart from that, all the rest of the existing system is applicable to underwater surveys (i.e. Waterproof PPM control box itself with its GPS option)

Willy

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Hi,

This is the drawings of the mechanical design of the Torpedo enclosing the watertight sensor container we provide with our MarkIV systems.
Willy

Posted on: January 19, 2012, 04:24:13 AM

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We have decided to make and provide our complete Torpedo for the MarkIVB systems.
This is the link to a simpler design which will probably be the base of our implementation:

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Willy

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