Not all vibration can be measured easily using traditional accelerometers and transducers, it maybe that the surface is very hot, moving, or coated such that a sensor cannot be attached. Equally the test piece might be difficult or dangerous to reach. In all these cases a laser Doppler vibrometer can assist as a contactless measurement method. Lasers can also speed measurements that would other take a very long time relocation test equipment by allowing all measurements to be taken from one point - For example the maintenance of bearings on a conveyer belt.
Xi Engineering Consultants utilise Polytec’s excellent range of laser vibrometers. Depending on application Xi can select the best laser and measurement system, be it long range, rotational, high frequency or otherwise.
Long range measurement
Typically long range laser vibration measurement was challenging, requiring near perpendicular positioning to the subject and highly levels of reflectivity of the subject surface. Polytec’s RSV-150 (Remote Sensing Vibrometer) over comes these hurdles, allowing long range measurements at low incidence angles and varying reflectivity at a bandwidth from 0 to 25kHz. Where surface reflectivity is good measurements can be obtained in excess of 300m.
The RSV-150 proves ideal for civil applications; Measurement of tall buildings, structures and bridges. Xi have also utilised long range laser vibrometers to assess vibration from wind turbines. This is a valuable technique as it allows measurement to take place with no disruption or costly shut downs to install sensors.
Torsional vibration and rotational vibrations can be very difficult to establish with traditional sensors. A laser vibrometer allows a contactless system to quantify the dynamics of a moving shaft with no risk to cable entanglement. Lasers can also be used to quantify the rotational dynamics of fan blades and other rotating objects establishing what the inertial impact there is on the blade resonance.
High frequencies are also possible to measure using laser systems with frequencies well above that of traditional piezo accelerometers. Using lasers upper measurement frequencies in excess of 250kHz are possible.