An add-on three-axis coil attachment is needed for QTFM Gen-2 to output vector field measurements. The coil attachment slides over the sensor head and connects to the electronics controller with a flexible ribbon cable.
QTFM is inherently a total field magnetometer and therefore it can only measure B0. However, with the coil attachment, QTFM G2 is sequentially subjected to pre-determined Bx, By, and Bz offset fields. From a measurement of the shift in B0 when the bias coil is on vs off, the vector components of the background field are mathematically calculated.
QTFM Gen-2 operates in a pulsed mode (link) in which one field measurement is made in a cycle that repeats every 1 ms. In scalar-only mode, a measurement of the total field [B0=√(Bx2+By2+Bz2)] is made in each cycle. When the hybrid vector-scalar mode is activated, the total-field and vector components are measured in interleaved cycles as shown in the figure below.
In cycles 1, 3, 5, … the sensor measures B0. In cycles 2 and 4, Bx coil is activated from which one measurement of the Bx field component is derived. Similarly, the By component is derived from cycles 6 and 8, and the Bz component is derived from cycles 10 and 12. In hybrid-scalar vector mode, the maximum data rate for B0 is 2 ms/sample, and 12 ms/sample for Bx, By, and Bz.
Benefits:
-Compared to fluxgate, QTFM vector output is extremely stable with no noticeable long-term drift or temperature coefficient
-High sensitivity
-B0, Bx, By, Bz measurements from a single device and same sensing region
Limitations:
–Designed for earth’s field operation, 10 µT to 200 µT
-Vector sensitivity degrades as the sensor head approaches a dead zone