Konstruktion av mätinstrument för vibrationsmätning

Sammanfattning: A mass imbalance in the driveline of a hydro power plant is a common source to vibrations. These vibrations have the frequency of rotation accompanied by harmonics and subharmonics. Vibrations cause ware and tare on components and in the long term defect bearings. Plant owners perform numerous tests to the driveline in order to detect harmful vibrations.Sweco Energuide AB, a company with consultant services within the energy sector, performs quality tests to plant owners including vibration tests of the driveline. The system they use for these tests is both expensive and time consuming to arrange for set-up. It is considered unpractical and a replacement is sought for.A team in Energuide, runs a project with the aim to develop a more suitable and cost efficient measurement device to replace the system used today. The goal is to build a more manageable device with equally high performance, to a lower cost. The device was determined to use laser measurement technique, as lasers are versatile and can be used in a number of applications.A large variety of sensors are available on the market today. Some use triangulation to detect vibrations, others use more advanced techniques such as Doppler effect sensors. These sensors are accurate but expensive and therefore excluded, due to cost efficient solution. One manufacturer offer an affordable series of sensors with gratifying performance to a reasonable cost. After a comparison, a suitable sensor was found and purchased from a local dealer.Data from the sensor has to be processed, calculated and stored by a unit called the data logger. Development of the data logger and to understand sensor functionality took most of the dedicated time, for making the measurement device. The data logger was encased in an aluminum cover, protected from shocks and potentially dusty environments. A sensor is connected by a plug-in cable and the device is controlled, using a keypad.Finally, the device was put to test by comparing its performance to the existing system. The task was to measure the vibrations of a generator bearing house. Both the existing measurement system and the device used an equal set-up, arranged under laboratory circumstances.Measurements were done “side by side”, to improve reliability for the outcome of the test. Results showed that the existing measurement system and the device had comparable performance. The existing measurement system is able to use a higher sampling rates, e.g. making it capable to detect vibrations at higher frequencies. However, the performance of the device was considered sufficient and may, in specific cases, replace the existing system. Further development is needed though, to fully replace the existing system. E.g. more sensors for simultaneous mesurements.