A coupling liquid is what allows ultrasonic digital thickness gauges to measure the thickness of a material by simply placing a probe on the surface. These instruments are part of the "NDT" category, non-destructive testing because they do not affect or alter the object in any way. In fact, digital thickness gauges use the ultrasonic measurement method and have a high reading speed.
Ultrasonic thickness gauges are also a necessary tool for those who deal with the preventive control of corrosion on tanks, tanks, pipes and all parts that could be subject to structural weakening, in the building, mechanical or industrial (plant) sectors. All this of course in addition to measuring the thickness of details such as pipes, sheets, etc.
When choosing a digital thickness gauge it is essential to take into account: