Ok, I can see the picture going through that site. I think the colours might have changed since there's no grey or white, but there is a green tube with a pair of bright blue lines horizontally in the middle.
Anyway, the drawing makes sense, and I can see what must be the bronze cover plate on the extreme right in the picture. The gasket doesn't show up as grey, but I think it must be behind the bronze plate?
Not 100% sure how it works, but if you're saying that there's some sort of 'piezoelectrical effect', then I can sort of imagine a bit.
Hmmm, where it's located, it must not even be inside the PH, so the transducer would be at the same pressure as the outside water perhaps, or so thick and small that it doesn't matter, and then it just sends the signal into the operator via a through hull.