Motor rotational speed monitoring device

The utility model provides a motor rotational speed monitoring device for listen the rotational speed of a motor. The rotation of sensory unit gear of this motor of sensing in a cycle time to produce a pulse wave signal that includes a plurality of pulse waves. A microprocessing unit according to this pulse wave signal obtain one about the pulse wave quantity of pulse wave to obtain one about in this cycle time according to this pulse wave signal pulse wave interval time between two last pulse waves in the pulse wave, and obtain one about in this cycle time end interval time between the final pulse wave in the pulse wave and this cycle time's concluding time point, last at least according to this cycle time, this pulse wave quantity, one about required the number of the gear teeth, this pulse wave interval time of this gear revolve round, and this rotational speed that finishes this motor of interval time acquisition. Any zoarium component of this motor that does not need to be changed is borrowed, more accur