Controlling/monitoring the thickness of applied paint in real time is important to many situations including painting ship and submarine hulls in dry docks for maintaining health of ships and submarines against the harshness of the sea, in automobile and aerospace industries, and in a variety of other industries as a control sensor that plays significant role in product quality, process control, and cost control. Insufficient thickness results to inadequate protection while overspray leads to waste and pollution of the environment. A rugged instrumentation for the real time non-contact accurate measurement of wet and dry paint film thickness measurement will be immensely valuable. As paint is applied with several layers of the same or different type, thickness of each newly sprayed wet layer is of most interest, but measurement on dry paint is also useful. In this study, we use acousto-optic tunable filter-based near infrared spectrometer to obtain the absorption spectrum of layers of paint sprayed on sand blasted steel surface and thus measure the thickness of coating under both wet and dry situations. NIR spectra are obtained from 1100 to 2300 nm on four sample of different thickness of paint up to 127 micron. Partial least squares model built with the spectra shows good correlation with standard error of prediction within ~ 0.7 micron. Results indicate that the spectra also respond to the amount of organic solvent in the wet paint and can be used to monitor the degree of dryness of the paint in real time.
We have utilized a traveling acoustic pulse in a two-mode optical fiber to create a moving beam splitter to couple light from LP01 to LP11 mode. As these optical modes have different group velocities, a variable intermodal delay is generated as a function acoustic pulse position in the fiber. The device can be used in low-coherence interferometry to scan time delay for making fast extended range absolute measurement using simple analog electronic circuits. With this scanning technique we demonstrate measurement of absolute strain over 1600 (mu) (epsilon) in the temperature range 20-60 degrees C with resolutions of the order of 40 (mu) (epsilon) and 0.7 degrees C, respectively, employing highly birefringent fibers as sensing elements.
We describe a technique that is used for the real-time measurement of the vibration of an object point. The technique can be used when the vibration is characterized by a large amplitude, i.e. several millimeters. The technique shows the additional advantages that it requires no special surface treatment and is insensitive to inplane object displacements. In this technique an object point is illuminated by a small diameter beam (at an angle) that is structured with straight parallel fringes. The illuminated object point is then imaged onto a Ronchi ruling. The total light transmitted through the Ronchi ruling is then used to recover the vibration of the object point, in real time, by using well known servo techniques.
The real-time measurement of the vibration of a point in a large vibrating object is an application that is often encountered in industry. Many laser based point vibration measuring devices have been proposed. All have their advantages and disadvantages and which one is used is determined by the application conditions.
The design, construction, operation, and preliminary evaluation of miniature fiber Fabry-Perot (FFP) interferometers used as heat transfer gauges is described. These gauges are being developed for a particular application where heat transfer data is currently obtained using conventional platinum thin-film resistance thermometers. The specifications that the sensors must exceed are: (1) temperature resolution of 25 mK over a 50 K range; (2) temporal response of 10 microsecond(s) ; (3) an ability to operate as a calorimetric heat-transfer gauge. The sensor consists of a short length of single-mode optical fiber (approximately equals 3 mm) to which low- reflectivity coatings have been applied at each end. It is illuminated and interrogated by an arbitrary length of addressing fiber. A laser diode is used as the source and the authors have exploited the facility to frequency modulate the diode in a novel signal processing scheme. To determine the performance of the sensor, short duration heat pulses derived from a pulsed Nd:YAG laser were applied to one end of the FFP. The response time was found to be 8 microsecond(s) and the sensor operation as a calorimeter was verified.