A nuclear thickness gage with improved response speed

The authors describe the conflict between measurement precision and speed of response in nuclear radiation thickness gages, and outline a method for improving the speed for step changes in thickness. Significant reductions in ISE between true thickness and gage output are obtained for ΔT as small as 3% of measured thickness. These reductions in ISE exceed 80% for ΔT as large as 10%. The threshold for triggering this fast response should be set at levels near ΔT=3% or more, and the fast response time constant should be selected as a function of the expected high frequency thickness change amplitude and the response time of the control system or data acquisition system interfaced to the gage. If the majority of the changes will be large, a time constant as short as 1 msec can be used in the fast mode. If the majority of the changes will be 3 to 5%, or if a slower control system is tied up to the gage, time constants as long as 5 msec may give the maximum benefit. In any case, the fast response mode can easily be tailored to the observed operating conditions