The permeable and saturation of magnetic core is excited by the drive circuit. In the permeable state, the magnetic flux is focused to the magnetic core; there is more magnetic flux in the inner of the measurement coils than the outer. In the saturation state, the magnetic flux is diverged from the inner of measurement coils. The magnetic core works as a gate for three measurement coils, which open or close the magnetic flux into inner of each coil, then change the amount of the magnetic flux, and induce a voltage pulse in each coil. In each exciting cycle, the gate state has changed four times, that will induce four voltage pulses: PICKUP1, PICKUP2, PICKUP3 and PICKUP4.
These voltage pulses from each measurement coil have been sampled and integrated in the circuit, accordance to the integration voltage the circuit supply feedback currents respectively to each of the measurement coils, which produce magnetic field completely offset the magnetic field ,as the result, the magnetic field in the inner of three measurement coils is zero. The triaxial fluxgate is closed-loop measuring, each of three feedback currents is exactly equal to each of three axis magnetic field components.
The Insert Drill Collar allows the three magnetic field components simultaneously to be measured at the same point in space, and only 12mm thick. The Insert Drill Collar adapted SOI (Silicon On Insulator) electronics wafer, hybrid circuit technology and hermetic seal packaging. Several technical improvements of circuits improved the Z axis and the X and Y axes frequency response of the phase synchronization. The phase shift of the Z axis is same to the X and Y axes in frequency response. Also bias, scale factor and open-loop sensitivity of Z axis are improved, and are the same as the value of the X and Y axis. The Insert Drill Collar is able to work in wide temperature range (-50℃ to +210℃) and to survive over 2000 hours.
Calibration coefficient after thermal modeling
The temperature range of thermal modeling is -50℃ to +210℃,the axis alignment is thermal modeled by zero order polynomial, the bias and scale factor are thermal modeled by third order polynomial.
Each unit will be calibrated before shipping and build up its own calibration coefficients file. To get the accurate X,Y,Z axis component the triaxial fluxgate output voltage shall be calculated with the calibration coefficient.
Calculation of temperature
TUM is output voltage of the temperature sensor, the unit is V. T is the current temperature, the unit is ℃.
Calculation of Scale and Bias
Calculation of three components of magnetic vector
FXUM, FYUM, FZUM are the output voltage of the triaxial fluxgate, the unit is Voltage. HX, HY, HZ are the three components of magnetic field, the unit is Gauss.