With the speed measurement , technical equipment is used to find out how fast an object is turning. The speed can be measured using the following operating principles:
Time measurement of one revolution
With photocells or other sensors, the switching time is measured which requires the object for one revolution. The speed is calculated with
Frequency measurement of vibration or noise
The speed of rotation of the rotating object is a main component in the frequency spectrum of the mechanical vibrations or acoustic noises generated on the machine. The speed can be determined by measurement (using a strain gauge , microphone , acceleration sensor , etc.).
Angle measurement at fixed time intervals
If the angles φ 1 and φ 2 at two time points , and are well known, the rotational speed calculated by
Here k is to be used in such a way that the numerator for a full angle results in the number one for one revolution, i.e. k = 1 / 2π = 1/360 °.
In industry, impulses on gears are often recorded without contact. The field plate sensors used for this supply pulses of up to 20 kHz.
The rotating object is flashed at fixed time intervals. If regular markings on the object rotate exactly by grid widths, the grid seems to stand still. The number of marks and the frequency of the stroboscope can be used to determine the speed.
Application e.g. B. the turntable .
According to the law of induction , the voltage in a coil is proportional to the speed at which the magnetic flux changes. A rotating permanent magnet generates an alternating voltage in the coil. The voltage level or the frequency can be used to measure the speed.
Rotating weights are pushed outwards by centrifugal force . A spring or the force of gravity create the balance of forces. The resulting movement is mechanically transmitted to a pointer. Today this method is seldom used for measurements, but due to the reliable operation without auxiliary energy, this measuring principle is used for monitoring the maximum speed of elevators , cable cars, etc.