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.
In parallel with this feature, we are also experimenting with an internal GPS chip option and an alternate Bluetooth connection to an external GPS device.
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