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. 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. 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
