FAQ (Frequently Asked Questions)
Does your acquisition system setup include one of our power supply or data acquisition units? If not make sure you have applied a suitable low pass filter in your setup to deal with the excitation frequency of the sensor. You can either apply an analogue low pass filter, or digitise the signal at a frequency at least twice that of the excitation frequency. Please refer to your sensor’s brochure for details on excitation frequency and breakthrough levels.
The output from the magnetometer is an analogue voltage which can be connected to the customers own appropriate data acquisition system(DAQ). It should be noted that there is some residual breakthrough from the sensors excitation which is partially filtered inside the sensor (by an analogue low-pass filter). This is then further filtered out by our power supplies and DAQs. If using own acquisition system, you would need to filter this out either by fitting an analogue low pass filter or by digitally sampling at least double the excitation frequency of the sensor. Alternatively, we could provide a PSU1 which would deliver power to the sensor and filter the output so that you can then connect it to your own DAQ without the need for additional filtering.
In order to achieve absolute measurements, scaling, orthogonality and offsets errors will need to be corrected. Multiple papers discuss the calibration of fluxgate magnetometers for use in total field measurements with varying level of success. One example is:
Munschy et al., 2007. Magnetic mapping for the detection and characterization of UXO: Use of multi-sensor fluxgate 3-axis magnetometers and methods of interpretation: Journal of Applied Geophysics, 61.
The scaling error is the difference between the applied field and the measured field. The scaling parameter will be stable over time, but is affected slightly by temperature changes. The scaling error is a stable value and, as such, a multiplying factor can be applied to the sensor readings to correct for it. Regular calibration will allow you to get the most up to date parameters for your sensor.
The orthogonality error is a constant error. It is due to the three axes not being exactly 90 degrees from each other. A correctional matrix can be applied to get the readings that would be expected if the axes were perfectly orthogonal to each other.
The range is included at the end of the sensor name. For example, a Mag-03MC70 is a Mag-03 with measuring range of 70µT. The range is also printed on the sensor’s label.
The noise is indicated by the letter found after the product/package reference. Q for very low noise (Mag-13 only), L is for low noise, no letter will indicate a standard noise and B a basic noise. Refer to the product datasheet for the noise levels. For example, Mag-13MCQ is an cylindrical package Mag-13 with noise level below 5pTrms/√Hz @ 1Hz.
Where possible, the fluxgate sensors are located in the centre axis of the sensor below the axes marking on the sensor. However, this is for indication only (and not always feasible to position the label right above the axes). For exact position, refer to the sensor’s outline drawing available on the product page at www.bartington.com.
Refer to the sensor’s outline drawing available on the product page at bartington.com as the mounting face change from sensor to sensor.
This is the amount of signal at the excitation frequency of the sensor present on the sensor’s output – please refer to glossary
Some sensors are designed for operation in vacuum (Mag-03IEHV for example – tested to pressure of 1e-4 Pa). Customers have in the past used non-tested sensors in low pressure environment, but we do not guarantee that the sensor will not be subjected to damage or severely outgas.
Only the Mag F and G probe are rated for cryogenic use. Sensors with integrated electronics will not operate at low temperature whilst other two parts sensors will suffer mechanical damage at low temperature (wire insulation breaking etc…). For high temperature use, only the Mag610/611 and Mag614 have been tested to operation above 175°C. This is the probe only – please refer to the individual brochure for specific operating temperatures.
Only a few of our aerospace and high temperature downhole sensors have been formally subjected to shock and vibrations tests (where applicable the test method is provided in the product datasheet). Other sensors have been used in those environment successfully over the years (for example Mag-03 are regularly mounted onto aircraft).
Most two part sensors have a maximum separation of ~5m. This depends on the sensor being used, to refer to the product datasheet for details.
If one sensor is active and the second one off, the sensors should be kept about 4-5cm apart (sensor dependent as the dimensions of the core material vary). The interference between two sensors as described above is a small DC offset on the active sensor. When the two sensors are powered (unless you are using multiple Mag612 or Mag619 with the excitation synchronised), the minimum distance should be between 15-20mm. A beating phenomenon may otherwise occur where one sensor is picking up the excitation from the other. As it is unlikely that the excitation will be at the same frequency and in phase, a beating (low frequency signal) appears on the output of the sensors.
No, these are not shielded, and can therefore be the source of noise pick-up in the system. It is therefore essential to shield these to prevent any issues.
The output voltage of ±10V or ±3V (full scale output dependent on sensor, please refer to individual brochures) represents the full scale range of your sensor. For example, if you have a ±100µT range sensor on a ±10V full scale output the scaling will be 100mV/µT. This voltage gives both the DC and AC components of the field.
As the sensors have an analogue voltage output, there is no defined resolution. Instead, the smallest fields detectable by a sensor are dependent mainly on the sensitivity of the voltmeter being used to read the output voltage, the internal noise of the sensor, and environmental noise. The internal noise of the sensor is the absolute minimum that the sensor can detect. However, the magnetic noise in the environment is higher than this, and will limit the smallest variation that can be detected. If data processing is performed, the environmental noise can be removed and the sensor noise level can be reached. The scaling (sensitivity of voltmeter) of the analogue output varies with the range of the sensor. Scaling values for different sensors are listed in the sensor’s datasheet. The scaling value increases as the range of the sensor decreases, increasing the sensitivity as the range is reduced.
We recommend that sensors are calibrated every 2 years. Sensors must be returned to Bartington Instruments for calibration.
We are unaware of anyone who has a design that you can use. However, Bartington manufactures the Mag-03-MC Mounting Bracket DR0746(2) for similar applications. For a drawing of the bracket, see figure 17 in the Mag-03 Operation Manual. This product could be adapted for your application.
It is very important to ensure that there is no steel in the tripod. We supply an aluminium tripod for mounting the Mag03MC, the Mag-03-T (Tripod). This extends to 1.3 metres, and comes with a tripod adaptor for mounting the Mag-03MC. Contact us at firstname.lastname@example.org for further details.
If it is saturated by an AC field, then it is not too much of an issue. If you can reduce the amplitude of the field progressively to come out of saturation (similar to what would be done during deperming) or stop the AC field when it is close to 0. If it is saturated at DC, or you switch off abruptly an AC field at high amplitude, then refer to the overload hysteresis figure in the brochure. Typically an offset will be added, the more important the offset for the higher the over-range.
There is always some overshoot above the full-scale output. Typically, the output of the sensor is driven by the op-amp on the electronics which will have an output function of the voltage supply. If you supply 12V, for instance, you may have a maximum output which will be around 10.5V. As you increase the voltage supply you can gain a few hundred mV on the output (we no longer guarantee that the output will be linear). So if you end up with field above 110-120uT, the output will reach the rail (which will be slightly above 10V) and stay there until the field comes back within sensor range.