A controllable bias field Bbias is applied to a single total-field OPM to maintain signal lock when an observable magnetic field Bmeas enters the OPM's dead zone. One or more electromagnetic (EM) coils are placed in proximity to the single OPM. Based on either a calibration of the field or a measured signal strength, a current command is calculated and applied to the one or more coils to produce the bias field Bbias to lift the observable magnetic field Bmeas out of the dead zone. The bias level is updated at a rate sufficient to maintain signal lock without interfering with the operation of the OPM. This allows a single OPM to sense the observable magnetic field Bmeas in all directions without having to either re-orient the OPM or to use multiple orthogonally positioned OPMs.