underwater pi

[gold1958]

Has anybody built a HH into a housing to be used underwater ?
Would a DD coil be better than a mono for this use ?
Also what adjustment should be made to pick up non ferrous metals?

[GT Blocker]

Has anybody built a HH into a housing to be used underwater ?
Would a DD coil be better than a mono for this use ?
Also what adjustment should be made to pick up non ferrous metals?

Hey Gold1958 - Allright...I'll jump in..
I am currently building the HH specifically for UW use in fresh water. I have an Ikelite UW flash housing to house the project. Other options can be found with a forum search. (BTW, Carl. what was the post on the Digikey hex nuts for potentiometer seals?)

As for the DD coils..unless I've missed something on these posts, a DD should be quieter and faster.

As far as non-ferrous/ferrous metals go, a PI detector doesn't discriminate. ALL metals(within the sample period and the target's decay curve) are detected. Small gold (itty bitty nuggets, toe rings, etc) requires a shorter sampling time and smaller/faster coils. If you plan to detect in salt water - forget about short sample times and small gold. See the other forum posts on the matter.

If I got something wrong, then someone needs to chip in on this.......
Gregory

[gold1958]

Great that makes sense. I have made housings from perspex for my video camera and lights tested to 80 m, so I will use the same type of housing.
The seal for the pot shafts are available from Farnell in the UK.
Which pots do you think are nesecary to mount externally?
With the DD coils am I right in saying theyare laid out in a figure of 8 the an overlap in the centre.

Saul

[GT Blocker]

controls and coils

Hey gold1958,
As far as the controls go, I would keep external U/W controls to the absolute minimum possible for your needs. With 35+yrs of diving under my weight belt (a lot of it professionally in film work), all I can say is, the simpler and easier to deal with while blowing bubbles, the better.
You'll have fewer disastrous leaks and less distractions, the former expensive and the latter potentially deadly, if not time consuming.

DD coils aren't figure eights but more like overlapping images in a pair of binoculars, if that makes any sense. Do a forum and board search and it should be more clear.
Hope that's of some help...GTB