Why is Shock Pulse Method (SPM®) able to measure at very low rotational speeds?To explain it one first has to look at the technique. There are two types of shocks generated by a bearing. To analyze them one has to look at the bearing rolling element and race contact area.
By testing many different size bearings under varying running speeds, SPM was able to establish a function that describes the relationship between the running speeds and size of the bearing and the shock level generated by that bearing. This relationship is expressed as a value which is called the initial (dBi) value. This value represents the shocks levels one would expect of a specific bearing running at a specific speed under ideal conditions. The measurements taken by the instrument measures the absolute shock pulse level and then subtracts the dBi value (which is calculated automatically when entering the running speed and diameter of the shaft/bearing to be measured), thereby giving an indication of how the bearing operating condition differs from the same bearing running at the ame speed but under ideal conditions. By further testing of different size bearings with different levels of damage SPM has been able to determine the acceptable shock pulse levels for all bearings under various operating conditions. In the case of slow rotating bearings shocks are still generated by the bearing as the lubricant is still subject to the same contact pressures and is forced into the surface asperities. Impact with debris or defects still causes shocks but these will have lower amplitudes as the impact speed is low. More FAQ...What does Condition Based Maintenance mean in 2008? What are Monitoring and Diagnostics Tasks? What are the Benefits of Condition Monitoring? Which is the most effective Condition Monitoring Technique? What are the parameters used in Vibration Sensors? |
During the development of the shock pulse method SPM found that the amplitude of the shocks generated by a bearing is a
function of the speed (and not the momentum) of the Rolling element.| Condition Monitoring Methods |
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Contact-free ID tags load the instrument with all measureing point data.
Special transducers for shock pulses and vibration assure accurate measurements.
Speed data are necessary for condition evaluation. Speed is measured by contact, or optically from a safe distance.