Still frame* from first video test at 234 metres: 30th July 2000
LNI 2000 now has tested a tv camera system capable of going to the deepest parts of Loch Ness.
Regular readers will know that the camera itself was built weeks ago, but the lighting system proved problematic.
One 20W halogen lamp was placed in a glass test tube and then sealed in forever like a ship in a bottle. It was ready for a deep pressure test but then a wire fell off inside, and the epoxy resin is permanent! On to...
Two more 12V halogen lamps (B&Q Downlighters) had their terminals and wiring potted in epoxy resin, and their halogen capsules left exposed., One was successfully pressure tested to 230 metres - without power. With power on, both failed within 5 minutes in the kitchen sink! On to...
Clearly, the halogen capsules could withstand the pressure of 23 atmospheres, but the wiring connections were the weak point. Any exposed conductors in close proximity simply corrode away. On the day before the camera test, after losing all 3 lamps in the space of 30 minutes, another "test-tube" unit was potted, and there was a little resin mix left over. I picked a 20W automotive halogen lamp out of the junk box and quickly painted its wires with nail-varnish before putting it in a cut-down 35mm film "pot" and pouring the rest of the resin around its base.
At the time the testing facilities were available, neither resin-potted lamp had set properly. There was no point in putting the test-tube lamp in the water because the pressure would simply drive the resin plug down to the far end of the tube, so the last-minute automotive lamp had to be used. Working in conjunction with the Loch Ness Project personnel on board MV "Deepscan", a temporary arrangement of camera, lamp unit and Ni-Cad battery was decided upon, with the power to the "naked" lamp being applied with a small crocodile clip once the lamp was in the water to prevent it shattering from thermal shock.
The only link between the camera and the surface was the 300 metres
of co-axial cable carrying the video signal. The loch was not as calm as
we would have wished, and the camera did stream at some angle away from
the boat, but we did manage to reach the bottom - ( at an indicated
234 metres), at times using all 300 metres of cable, and obtained about
20 minutes of bottom video record. The video signal was recorded and displayed
on a Sony DC-TRV 900 camcorder.
There were four elements involved in the underwater part of the test.
1. The Camera
2. The Lamp
3. The Battery
4. The Cable.
1. The camera worked, and provided a good video
signal through 300 metres of cable.
2. The lamp survived, and may well evolve into a permanent option with the addition of a suitable reflector. For the purpose of the test it was attached directly to the camera, but will now be moved to a more usual position some distance away to avoid lighting up the particles close to the camera.
3. The Ni-Cad battery pack, itself embedded in resin which has steadfastly refused to harden, surprising neither imploded nor exploded, and will continue to be used until it decides to cease co-operation one way or the other. It is well over twenty years old, having been removed from a Pye Reporter portable radio pack. Perhaps it will just fade away.
4 The cable, being brand new and carefully jointed, and carefully stored on a purpose built winding drum, flooded during the trials, via a series of tiny pin-prick punctures. (My cats have been interviewed regarding this but, like any decent government, "deny knowledge".) As it was brought to the surface and wound onto the drum, these punctures acted like so many little water pistols squirting the personnel at random with each revolution of the drum, and hissing like a nest of vipers. In time, the electrical properties of the cable will be affected, so ideas for a replacement "solution" will be welcomed. Ideas re fibre optics particularly so, and there is a requirement for more than just video to be sent from the bottom. Suggestions involving sacks and cats will not be entertained.
It worked. Now it must be assembled using a proper steering vane, and can then be used for dives to any depth. The present battery pack has a theoretical capacity of 7 Amp-Hours, which equates to a 4-hour dive duration with the single 20 Watt lamp.
*The angular shadow on the still frame is caused
by the crocodile clip connector hanging directly in front of the lamp!
The camera is angled steeply towards the bottom, and the picture quality
is adversely affected by the 20W lamp within 50 mm of the camera lens.
The loch bottom appears to be quite interesting with a varied surface of mainly dark sediments and occasional light patches. No living creatures were observed.
Many thanks to all involved in the testing!
© Dick Raynor. 31st July 2000.