Shock pulse measurement principle a [m/s²] 4.0 3.5 3.0 Roller bearing signals in 36 khz range Natural sensor frequency = 36 khz 2.5 2.0 1.5 1.0 0.5 0.0-0.5-1.0-1.5-2.0-2.5-3.0-3.5-4.0 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 t [ms] Sensor coupling methods Resonance f sensor f signal, roller bearing Approx. 36 khz db 36 khz 36k Hz Signals are recorded with high sensitivity due to resonance Meas. variables: db max and db carpet Info on shocks and rolling noises Unit: db, decibel (sound) Representation: y-axis is on a logarithmic scale; Up to 15,000 units from 0..99 db Measuring range: -9 db to 99 db (definition: 10 mv input signal on measuring device = 0.0 db) 68
Normalization of shock pulse measurement 1 db a Taking into account of: Signal loss Bearing load Other influences db i Taking into account of: Speed Shaft diameter db i + db a db ia (Attention: the db a value is generally negative) By using db ia, the warning and alarm thresholds do not need to be adjusted separately for every bearing. 69
Normalization of shock pulse measurement 2 Normalization not adjusted Normalization adjusted SP db sv SP db sv 90 db n 60 35 20 Sensor coupling and signal damping Not yet taken into account db n 60 35 Roller bearing Good condition: db n 60 35 Roller bearing damage 90 20 20 db i db ia db ia 0 0 db i = initial value Basic normalization for shock pulse level Derived from rotational speed and shaft diameter db ia = adapted initial value The signal attenuation at the actual measurement location is compensated in addition Influencing factors such as bearing load, type of roller bearing and lubricant can be taken into account 70
Rules for selecting measuring locations Sensor in load area, close to roller bearing (damping) Measuring direction of sensor toward load area No additional gaps (reflection, damping) Optimal area: 45 to the vertical axis on the bottom or the horizontal axis Especially important for large machines (P > 300 kw, n < 400 rpm ) Load area Load area 71
Load zone at belt drive Belt drive F d F s1 - Force of inertia F s2 - Belt tension F dyn - Belt vibration if belt tension is low or belt fault F s1 F s2 F res Measuring direction Load zone 72
Transmission of high frequency vibrations 1. Measuring direction toward load area 2. Structure-borne sound transmission as direct as possible... No additional gap... Do not measure "around corners" 3. Shortest possible transmission route 4. Measurement in load direction... In load area in lower part of housing 73