Recording the classical force acting on a quantum oscillator

With the aim of discovering practically realizable operations that satisfy the criterion of a "nonperturbing measurement", quantum analysis is performed of a specific measuring system including a test oscillator and a recording element - an RC sensor. It is shown that the sensitivity to external force may be the best characteristic quantum standard if the oscillator is an excited state. For a vacuum state of the oscillator, quantum fluctuations of the RC sensor limit the sensitivity at the typical level $\tau^{-1}(m\hbar\omega_0)^{1/2}$.