a device used to obtain the derivative with respect to time of a value fed into the device. The input value may be a variable angle of rotation of a shaft or a variable electrical quantity. The output signal of a differentiating device
characterizes the rate of change of the input value.
Differentiating devices are used in computer equipment, as well as in automatic control systems. The devices are classified as mechanical (frictional and centrifugal), electrical (differentiating circuits and active electronic differentiating elements), or electromechanical (tachometer alternators or DC generators).