A Contact-Less 2-Dimensional Laser Sensor for 3-Dimensional Wire Position and Tension Measurements

We have developed a contact-less two-dimensional laser sensor which combines position and tension measurements of wires with a diameter of order 0.2 mm. The sensor consists of commercially available laser pointers, lenses, color filters and photodiodes. In our application we have used this laser sensor in conjunction with an automated three-dimensional coordinate measuring machine (CMM). The device allows for a position measurement of wires in three dimensions with an accuracy of about 10 ¿m. At the same time the wire tension can be determined with an accuracy of 0.04 N. The device is operated at a distance of 150 mm from the wire. For each position measurement, the laser sensor is moved by the automated CMM into a plane, where the coordinates at which the wires intersect with this plane are determined. The position of the plane itself (the third coordinate) is given by the third axis of the CMM which is perpendicular to this plane. The precision of the device was determined using stainless steel wires with a diameter of 0.2 mm and a tension of 5 N. We use the sensor for quality assurance of the wire electrode modules for the KATRIN neutrino mass experiment. These modules are comprised of two layers of wires, which are 70 mm apart. In general, the device presented here is well suited for the measurement of any complex wire chamber geometry.