Figure 3
Automated field nulling based on reference measurements. (A) A reference array of four Gen-1 QuSpin OPMs is used to measure the vector field components Bx, By and Bz at two locations separated in the z direction. (B) To drive a single coil two PID controllers are used. One uses Σ to drive the sum of the field at the two locations (driving for example the Bx field down towards zero). The second PID uses ∆ to drive the difference of the field at the two locations (the gradient Gx) towards zero. Currents which are the sum and difference of these values are then applied to the planes.
