Vector
Magnetometers
|
|
|
In the past, magnetic observatories
relied on a combination of Overhauser, fluxgate and theodolite
instruments for obtaining measurements. GEM then introduced the dIdD
(delta Inclination / delta Declination) system for high precision
results.
Now, the dIdD has been enhanced significantly with the development of
the Suspended dIdD system. |
|
Observatory
Applications
As
described by the Israeli Nuclear group, Soreq,
the dIdD is a vector magnetometer offering monitoring of the
inclination and declination as well as total intensity of the earth
magnetic field. Resolution is 0.01 nT with a recording interval of 5
samples per second.
The Suspended dIdD instrument is the total field magnetometer / gradiometer
of choice for customers who require:
Minimal drift
Simplified observatory setup
Minimized ongoing system calibrations
Continuous, stable measurement
Reliability
Compact size
Suspended dIdD Benefits
The Suspended dIdD takes advantage of many of the benefits of the
Overhauser system.
In addition, it offers its own unique benefits for observatory work:
Temperature coefficients that reduce drift to less than 0.1 nT /
°C for high-end fluxgate
magnetometers.
Physical suspension of the Overhauser sensor. This has been
shown experimentally to contribute to reduced drift.
Long term drifts that are less than 2 nT / year. This figure
matches or exceeds the best component measurement at any observatory.
Simplification in setting up magnetic observatory installations.
The new Suspended dIdD eliminates the need for fluxgate magnetometers and
thermal insulating structures. In addition, the new system minimizes
ongoing system calibrations, which, in turn, frees personnel to
concentrate on more essential tasks such as interpreting and
understanding data.
Proven construction for high reliability. GEMs systems are
designed for robustness from electronics to sensors. Ultimately, the
system also exceeds specifications set by Intermagnet - the global
network of observatories monitoring the Earth's magnetic field
(www.intermagnet.org).
Understanding the
dIdD Measuring Sequence
The Suspended dIdD is a vector magnetometer for continuous monitoring of
the inclination, declination and total intensity of the Earths magnetic
field. It is this combination of measurements that sets it apart from
fluxgate instruments (i.e. fluxgates only provide inclination and
declination).
GEMs dIdD employs a mutually orthogonal coil system that measures one
unbiased and four biased values of total magnetic fields. The axes of
the coil system are arranged so that the axes of the mutually orthogonal
coils are themselves perpendicular to the Earths magnetic field vector,
F, in the horizontal plane and vertical geomagnetic meridian plane.
The measurement process is as follows:
1. Initially, equal and opposite currents are sequentially introduced
in to the Inclination (I) coil oriented perpendicularly to F.
The
resultant deflected values of F (Ip and Im) are recorded by the
Overhauser magnetometer. The undeflected value is also recorded.
2. Then, equal and opposite currents are sequentially introduced into
the Declination coil (D) which is also perpendicular to F. The D
deflection fields lie in the magnetic East
West direction. Resultant deflected values of F (Dp and Dm) are
recorded. The Overhauser magnetometer also records the undeflected value.
3. A simple algorithm is used to determine the subsequent changes
instantaneous angular changes between the coil axes and the direction of the Earths
vector, F. These angular changes are dI and dD. Adding dI and dD to baseline values of
Inclination and Declination for the coil system gives the instantaneous
Inclination and Declination values of F.
(Baseline values are determined from absolute measurement.)
The pulsed sequence preserves power; in practice, users acquire readings
on demand and save batteries. The continuous sequence polarizes
continuously and stops with very small interruptions of a few tens of
miliseconds; users can acquire data without losing any interval and
obtain full coverage of the terrain.
dIdD
Magnetometer Software
The dIdD data aquisition /
display software is an interactive Windows 95 / NT interactive interface
supplied with the dIdD vector magnetometer system. It functions as the
instrument's bi-directional RS-232 terminal. The dIdD software offers
the user the option to save the instrument readings to a disk file,
while displaying the incoming data in text and graph modes.
The dIdD chart recorder
displays the incoming data versus time. The vertical and horizontal
scales are calculated automatically so as to display the data within the
window. The user can change both the vertical and horizontal increments.
The window is divided into ten horizontal and ten vertical increments
(by dashed lines). The displayed profile can be scrolled both
horizontally and vertically. These changes can be achieved by selecting
the appropriate item from the Chart Recorder menu, or alternatively, by
using shortcut keys.
For more information
The Suspended dIdD takes advantage of many of the benefits of the
Overhauser system and the
Overhauser
product pages may be a useful reference. For more information on Overhauser technologies, please
refer to the
technical papers on this site.
The
Suspended dIdD brochure
provides detailed specifications.
If you would like
information specific to your work, please visit our
Quotations
area and submit a Request for Quotation. We would be delighted to
provide you with a no-obligation quote suited to your exact needs.
GEM Advanced Magnetometers.
Our World is Magnetic.
Applications
