NDT
INTERNATIONAL, INC.
NDT-710
Thickness
Gauge
3
It is practically impossible to efficiently transmit ultrasound from the transducer to the object to
be measured without the aid of a suitable coupling medium, usually referred to simply as
couplant. Couplants frequently used for thickness gauging are water, oil, gel, glycerin, and
propylene glycol. In practice, a small amount of couplant is applied between the transmitting
face of the transducer and the test surface.
WHAT MATERIALS CAN BE MEASURED?
Virtually any engineering material can be measured ultrasonically. Ultrasonic thickness gauges
can be set up for metals, plastics, ceramics, composites, epoxies, and glass. Liquid levels and
biological samples can also be measured. Materials generally not suited for conventional
ultrasonic gauging include wood, paper, concrete, and foam products. Online or inprocess
measurement of extruded plastics or rolled metal is often possible, as are layers or coatings in
multi layer materials.
THINGS TO CONSIDER
For any ultrasonic gauging application, the choice of gauge and transducer will depend on the
material to be measured, thickness range and accuracy requirements, geometry and
temperature, and any special conditions that may be present. Listed below, in order of
importance, are brief descriptions of some of the conditions that should be considered.
