Pressure Compensation (logging)

[Rmechanical]

I need to do reaserch in pressure compensation for logging tools, but I've had no luck in finding a good example or diagram.

Can someone point me in the right direction? because I've never seen a device like that in real life or even on pictures! I'm pretty lost. A simple diagram explaining the main components and design and formulas would be great. I'm sure I can adapt the design to my specific application.

Thanks.