Test Ideas: Helmet tester verifies compliance

A USB data-acquisition module collects accelerometer data to evaluate the impact of a helmet crash.

By Aniket, Consultant for Aum ElectroTech, Mumbai, India -- Test & Measurement World, 6/1/2010 12:00:00 AM

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Helmets are designed to minimize or prevent injury in a variety of activities, and they must be tested to ensure they meet industry standards for withstanding impacts. My company has developed a test system that evaluates a helmet's impact attenuation by releasing the helmet from a specific height in guided free fall on an impact anvil. An accelerometer (‘g' sensor) measures the force that would be transmitted through the helmet to the wearer's head and compares it to specified performance limits. A LabView application running on a standard PC controls the tester. Although this tester uses a USB data-acquisition module, it could also work with a PCI card in the PC or with a PXI card in a chassis.

Figure 1. In this configuration, an impactor drops onto a helmet, where sensors record speed, impact attenuation, and other parameters.

The impact test system has a firm pedestal, a linear bearing rail, a lift carriage, a drop carriage, and a digitally controlled Panasonic servo motor to lift either the striker or the helmet,  depending on the test. Figure 1 shows the helmet in a stationary position with the striker able to move as required. The test operator positions the striker, which is mounted to the drop carriage, and programs the desired drop velocity. The drop carriage automatically lifts to a height corresponding to the desired impact velocity. The drop tower complies with the helmet-test standards specified by numerous standards bodies.

Figure 2 shows how the test instrumentation connects to the sensors and the helmet. The data-acquisition module uses its digital-output lines to set the motor's direction so it raises or lowers the striker or helmet, while another digital output controls the motor's speed. An encoder senses position markers on the shaft and transmits pulses to a digital-input line, which tracks the anvil's location relative to a starting location.

Figure 2. An automated test system measures the g force on a helmet under test.

A test operator enters information about the helmet size, conditioning environments, and test standard into the system. Test screens that are specific to the test apparatus, standards, and routines let operators perform pre- and post-test instrument verification; then, the system performs the entire test sequence on a helmet.

The results from each test are instantly displayed both numerically and graphically by the LabView application, which also saves the data to a database for later review. (The LabView Database Connectivity Toolkit simplifies record keeping.) When testing is complete, the LabView Report Generation Toolkit produces a test report (including a PDF version); it can also send the report by e-mail to a specified recipient. Test-result documentation includes impact attenuation, retention elongation, helmet stability, penetration resistance, mass, center of gravity, and moment of inertia.

Test screens that are specific to the test apparatus, standards, and routines let operators perform pre- and post-test instrument verification.