Electronics
Can the QZFM sensor head be operated without the electronics module?
No. Sensor is not stand-alone and requires its own dedicated electronics unit.
Can I swap sensor and electronic units?
No. Each electronics unit is paired with a sensor module with unique values that optimizes the sensor operation. Randomly swapping the electronic units and sensor heads will likely damage the sensor. To swap electronics, you must contact us and we will provide you accompanying firmware update to enable such swaps if necessary. The serial number on the electronics unit must match that on the sensor.
Analog Output
What is the output scaling for analog output (B to V conversion)?
The QZFM analog output in default gain setting is 2.7 V/nT. The rail-to-rail output is +/-5V. In low gain mode, the output is 0.9 V/nT and in high gain mode, the output is 8.1 V/nT.
Is 16-bit ADC enough to read analog output?
In default gain setting, the output is 2.7 V/nT. Thus, the rail-to-rail output of the magnetometer is +/- 1.85 nT. If you have a 16-bit ADC (+/-5V setting), the noise floor will be 2 x 1.85/(2^16x sqrt[samplin speed]). If your sampling speed is 2 kHz, the noise floor of the ADC will be 3 fT/rtHz, which is below the noise floor of the sensor. If you have concerns, you can run the sensor in the high-gain setting.
Internal Coils
What is the maximum background magnetic field amplitude that the QZFM sensors can operate in?
~50 nT. QZFM is an absolute zero field magnetometer and operates best (<1% non-linearity) when the background field is < +/- 1 nT. Since most magnetically shielded rooms/cans have 10’s of nT residual field, for convenience, we have added magnetic coils surrounding the sensor to null residual magnetic field internally. Thus even when the sensor is placed in, let’s say, 50 nT residual field, the sensing element sees 0 nT after internal coils are activated.
Do internal coils continuously compensate background fields?
No. The internal field zeroing algorithm is only active when you press “Field Zero”. When “Field Zero” button is released, the feedback loops are deactivated and the coil current is held at a constant value. Thus, every time you move the sensors substantially or when you suspect the background field has changed, you must re-zero the fields.
Why can’t the QZFM built-in coils be made to compensate for larger than 50 nT fields?
Two reasons. First limit on the field is set by the signal-to-noise ratio (SNR) of our digital-to-analog converters (DACs) that control the field. The second limitation is the field inhomogeneity of our internal coils. Inhomogeneous field broadens the zero-field resonance which lowers the sensor performance.
User Interface
What do the LED lights on the front panel of the electronics module indicate?
The four lights indicate the state of the sensor. They correspond to the four virtual indicators in the QZFM UI and provide information on the status of the sensor. When all four lights are amber, the sensor is in the powered but not operational state. During the Auto Start procedure,