A basic distinction is made between a contacting and non-contacting thickness measurement. The choice of method to be used depends on different criteria:
- material composition (homogeneous or inhomogeneous)
- material structure (solid, ductile or e.g. sticky)
- material thickness to be measured
- required accuracy
- measuring spot size
- measuring speed
Tactile measurement systems operate mainly with measuring rollers or rails which are pressed onto the material at different forces and the thickness is then determined by the amount of their deflection.
Non-contact systems usually use laser, ultrasound, capacitive, inductive or air-cushion sensors as well as radiometric sources of radiation as measuring transducers. Each of these measuring methods has specific advantages and disadvantages depending on the material to be measured which favour or restrict its application or make it impossible.