On the example of an electromechanical system with a one-link manipulator, tracking a given angular position of the manipulator is considered under the following conditions: the output (adjustable) variable is not measured, the sensors are located only on the drive; external and parametric disturbances act on the mechanical subsystem. Discontinuous control law is formed in terms of the canonical input-output system, written with respect to the tracking error. To implement the control law under conditions of incomplete information, a double-circuit observer with piecewise linear corrective actions has been developed. In the first loop, via the observer constructed as a replica of the electrical subsystem, an unmeasured controlled variable is reconstructed, which, together with the reference action, is the output of the second loop. The second observer is constructed as a replica of the canonical input-output system and reconstructs the mixed variables. These are functions of state variables, external influences and their derivatives, according to which feedback is formed. A procedure for adjusting the parameters of observers that provide estimation with a given accuracy for a given time has been developed. When a double-loop observer is implemented in a tracking system, it is not required to further expand the state space due to generators of external influences, it is enough to know the areas of their change. As a result, in a closed system without re-tuning the regulator, various operating scenarios are supported when external factors change within acceptable limits.