Application: Measuring the thickness of gelcoat over fiberglass. Gelcoat is normally measured with a delay line transducer. The most commonly recommended transducer is the Panametrics-NDT M208-RM (20 MHz, 0.125 in. element). In cases involving thick gelcoat, the M202-RM (10 MHz, 0.25 in. diameter element) can also be used. Because manufacturers are usually most concerned about insuring that gelcoat meets a minimum thickness specification, the recommended procedure is to make several readings within a small area and record the minimum reading obtained. If a waveform display is available, then it is possible to verify whether the first returning echo (representing minimum gelcoat thickness) is being detected, by monitoring the waveform display as seen in the screen images below. If a Model 45MG is used without the waveform display option, it is particularly important to note the minimum reading within a local area. Any abrupt transition to a higher reading usually represents false detection caused by irregular echoes. As a general rule, gage gain should be set high to maximize the likelihood of detected the first returning echo. The "First Peak" detection mode that is available on most models is also useful in this application to help insure measurement of minimum thickness.
Note: Measurement of total fiberglass thickness |