| 摘要 |
It is foreseen to measure the rotational speed (v) of a motor by measuring the electromotive force (e.m.f.), calculated at any moment as the difference between the feeding voltage and the voltage drop across the armature resistance (Ri), or as the value of the voltage in the instants when the current reaches the zero value. In the first embodiment, an element that calculates the value of armature resistance (Ri) at consequent instants (t1, t2) is foreseen and which then calculates the values of the electromotive force (e.m.f.) from the equation e.m.f. = Va - Ri x I. In the second and third embodiments, the value of the electromotive force is found directly by measuring the voltage (Va) during the instants in which the current (I) reaches the zero value, through a current meter followed by a current sampler and a memory. From the value of the electromotive force (e.m.f.) the rotational speed of the motor is obtained by means of the equation v = e.m.f./k, where k is a constant characteristic of the motor. |
