A method and apparatus for conducting water intrusion tests on hydrophobic filtration units is disclosed. A propagation time of the ultrasonic wave in the suspension is determined. The diameter of the thread on the tail portion is greater than that of the thread on the lead portion, and in which the thread lead of the thread on the lead portion is equal to the thread lead of the thread on the tail portion. The axial motion detector detects the axial movement of the device and if the axial acceleration is below a pre-determined threshold, disconnects the power supply thereby preventing the acquisition of redundant images.