German Railway is using strain gauges from measurement technologist HBM to protect touch screen ticket machines from vandalism. The vandal-proof touch screens are formed by placing unbreakable glass in front of a normal computer VDU.
At each corner of the frame is an HBM DBB01 sensor, consisting of an aluminium double bending beam connected to foil strain gauges. The double bending beam allows for overload protection, and the metal construction means the sensor can withstand a peak force five times the nominal load, for example a baseball bat attack.
With foil strain gauges, the strain induced depends only on the magnitude of the force and not on its frequency. Unlike some piezoelectric devices, vibrations from a passing train will not trigger the sensors, yet the foil will detect people who only touch the screen lightly.
HBM, Great Britain. Reader Enquiry Number 140
