speed measurement
Distance, speed and acceleration are directly related by physical laws. In velocity measurement, a distance (s) determined by sensors is related to the time (t) required to cover the distance. The velocity (V) is calculated from the quotient of the distance to the required time.
In electrical measurement technology, all common methods can be used for distance measurement. The temporal reference is established by time elements. Signal propagation times also provide information about a distance covered by electrical signals. For example, the distance of a cable break can be determined from the propagation time of signals reflected at fault locations. This measurement method is used, for example, in time domain reflectometry(TDR) and optical time domain reflectometry( OTDR).
In addition to the sensor systems described below, differentiators and integrators are also used to measure velocity and acceleration. The acceleration (a) is calculated from the quotient of the velocity change (delta V) per time unit (t). Acceleration transducers are used to determine acceleration.
Spring-mass systems: These sensors use the effect of acceleration on a damped spring-mass system.
Capacitive accelerometers: Capacitances are used in these sensors to measure the displacement of masses. Here, the mass (m) is suspended in a differential capacitor in such a way that the plate spacing, and thus the capacitance of the capacitor, is changed during the motion caused by acceleration. While the capacitance of one capacitor increases when the plate spacing is reduced, it decreases for the other. The change is evaluated by a bridge circuit.
Magnetic and inductive accelerometers: The magnetic accelerometer uses the Hall effect and has a permanent magnet that serves as the accelerating mass (m). The permanent magnet changes its distance relative to a Hall sensor.
Piezoelectric accelerometers use the piezoelectric effect. When a load is applied to the surface, a charge is generated that is proportional to the force. The voltage converted from the dissipated charge is used to determine the acceleration from the physical relationship of force, mass and acceleration.