Abstract <p>The problems associated with belt elongation in belt drives and proposals for a new method for monitoring their conditions based on ferroprobe magnetic sensors are discussed. The main reasons for reduced efficiency of a belt drive, such as slippage, vibration, and plastic deformation, are described. The existing control methods and their advantages and disadvantages are considered. An innovative approach is proposed that permits noncontact and continuous monitoring of belt conditions with high accuracy. This method is based on the use of a magnetic mark and two ferroprobe magnetically sensitive sensors recording the time of passage of the mark and permits calculation of the speed and length of the belt. A mathematical model for calculating the belt length is presented, and the features of implementation of the system are described.</p>