An automated magnetometer suitable for long lasting measurement under stable and controllable experimental conditions has been implemented. The device is based on coherent population trapping (CPT) produced by a multifrequency excitation. CPT resonance is observed when a frequency comb, generated by diode laser current modulation, excites Cs atoms confined in a $\pi ∕4\times {\left(2.5\right)}^2\times 1{\mathrm{cm}}^3$ , $2\text{\hspace{0.17em} Torr}$ ${\mathrm{N}}_2$ buffered cell. A fully optical sensor is connected through an optical fiber to the laser head allowing for truly remote sensing and minimization of the field perturbation. A detailed analysis of the CPT resonance parameters as a function of the optical detuning has been made in order to get high sensitivity measurements. The magnetic field monitoring performances and the best sensitivity obtained in a balanced differential configuration of the sensor are presented.