Arrangement for measuring the velocity and/or the length of moving objects.

摘要

The invention relates to a method of and an arrangement for measuring the velocity and/or length of moving objects in accordance with the Doppler principle.
<??>If the velocity of objects must be measured over a wide range then the problem is encountered that stringent requirements must be imposed on the bandwidth of the electronics which must process the Doppler shift. The method according to the invention has for its object to measure velocity and/or length accurately using simple, narrow-band processing electronics by imparting a pre-shift to the frequency of the electromagnetic wave directed towards the object to be measured, which pre-shift is opposite to the Doppler shift generated by the movement of the object. The pre-shift can be realized by imaging a light beam originating from a laser on the object via a rotating phase grating. The rate of rotation of the phase grating is controlled so that the total Doppler shift measured is always constant.