Ultrasonic Film Thickness Gauge

An Ultrasonic Film Thickness Gauge like DeFelsko's Positector 200 probe emits a high frequency sound pulse that travels into the coating via a coupling gel and reflects from ANY surface that is different in density.

The readings of a ultrasonic film thickness gauge are obtained by measuring the time taken for the sound pulse to propagate from the probe to the coating/substrate interface and back.

How does an Ultrasonic Dry Film Thickness Gauge work?

The simplest mental model is that the probe is a transducer, so it acts as both a sound source similar to a speaker and as a microphone.

Coatings will carry this sound and any interface between layers of coating or the coating and the substrate will reflect the sound back to the probe.

The probe records as would a microphone, producing a sound record which is displayed to the user as a simplified graphic.

The thickness is marked on this graphic, under default settings the thickness is marked at the indicator for the loudest sound reflected from the coating/substrate system.

How do you operate an Ultrasonic Dry Film Thickness Gauge?

The measurement of coating thickness with an ultrasonic gauge is a three stage process.

1. The operator uses the gauge to record a single measurement
2. The gauge will provide a graphic of sound recorded from reflections with and at the boundary of the coating
   
   1. A thickness value will be indicated by the gauge on this graphic, marking a possible thickness reflection from the boundry of coating and substrate
3. The operator will review this graphic and the indicated value and choose to;
   
   1. Accept the machines indicated value as correct, confirming the automated selection matches the real thickness
   2. Adjust the parameters of the gauge such as Low and High gate values, or the use of a Threshold value to adjust the machine's choice to the correct reflection and so the thickness measurement
   3. Reject the thickness measurement if the graphic does not show a valid test

How is Ultrasonic Film Thickness Calibrated for a Material?

The Thickness Calibration function of an ultrasonic gauge is used by the operator to conform the indicated thickness measurements to physically measured samples of specific materials, such as waterproofing membranes or paint types. It is critical to perform a thickness calibration so the Gauge measures at the limit of its accuracy and precision.

The gauge will record a Calibration Value tied to the material, this calibration value is based upon a calculation of the speed at which sound is transmitted through the coating material/s.