Optical sensor for measuring rail displacement in a rail accelerator during electromagnetic launch
conference paper
An optical measurement system has been developed to measure the displacement of the rails in an electromagnetic rail accelerator during launch experiments. By measuring the displacement of both rails at a certain distance from the breech, the bore growth during launch at that position is obtained . The results of these measurements are useful for studying the interaction between the rail accelerator and the solid brush armature.
A measuring method with optical fibres has been chosen to eliminate the effects of electromagnetic interference. Each sensor consists of two bundles of optical fibres which are distributed homogeneously over the cross-section of a thin metal tube. One fibre bundle is attached to a light source, the other is attached to a photo diode. The tube is positioned inside a diagnostics access hole of the rail accelerator, facing the backside of the rail. Light from one fibre bundle is reflected at the surface of the rail and is collected by the other bundle. The amount of light, detected by the photo diode, is a function of the distance between the sensor tip and the reflecting surface. The reflectivity of the rail surface influences the output voltage of the detection circuit. Therefore, each sensor is calibrated, facing the same rail surface during calibration as during the actual measurement. A fit of the calibration curve is used to transform the measured voltage signal into displacement data. The sensitivity of the measuring system depends on the range, which is adjustable from 50 μm to 500 μm. The resolution is 1.6 % of the measuring range.
Experimental results, obtained during launch experiments with multi-fibre solid brush armatures, are compared with results of a one-dimensional, time-dependent model that calculates the rail accelerator response to pulsed electromechanical loading. The model considers the rail accelerator as a damped mechanical translation system and is used to analyse the experimental data qualitatively.
A measuring method with optical fibres has been chosen to eliminate the effects of electromagnetic interference. Each sensor consists of two bundles of optical fibres which are distributed homogeneously over the cross-section of a thin metal tube. One fibre bundle is attached to a light source, the other is attached to a photo diode. The tube is positioned inside a diagnostics access hole of the rail accelerator, facing the backside of the rail. Light from one fibre bundle is reflected at the surface of the rail and is collected by the other bundle. The amount of light, detected by the photo diode, is a function of the distance between the sensor tip and the reflecting surface. The reflectivity of the rail surface influences the output voltage of the detection circuit. Therefore, each sensor is calibrated, facing the same rail surface during calibration as during the actual measurement. A fit of the calibration curve is used to transform the measured voltage signal into displacement data. The sensitivity of the measuring system depends on the range, which is adjustable from 50 μm to 500 μm. The resolution is 1.6 % of the measuring range.
Experimental results, obtained during launch experiments with multi-fibre solid brush armatures, are compared with results of a one-dimensional, time-dependent model that calculates the rail accelerator response to pulsed electromechanical loading. The model considers the rail accelerator as a damped mechanical translation system and is used to analyse the experimental data qualitatively.
Topics
TNO Identifier
124028
Article nr.
97
Source title
5th European Symposium on EML Technology, Toulouse, France, 10-13 April 1995
Collation
8 p.
Place of publication
Rijswijk
Files
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