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MAGNETOMETERS. Kedrick Black. ECE 5320 Mechatronics Assignment #1. Definition of attitude control Description of a magnetometer How the magnetometer works in general Types of magnetometers Real time monitoring of the earths magnetic field How the magnetometer works in space

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slide1

MAGNETOMETERS

Kedrick Black

ECE 5320 Mechatronics

Assignment #1

Kedrick Black

slide2
Definition of attitude control

Description of a magnetometer

How the magnetometer works in general

Types of magnetometers

Real time monitoring of the earths magnetic field

How the magnetometer works in space

First magnetometer used in space

The ideal magnetometer

Design tradeoffs for magnetometers

Example placement on spacecraft

Calibration

Testing

Fluxgate magnetometer

Honeywell 3-axis magnetometer

Limitations

Places to buy/Cost

OUTLINE

Kedrick Black

slide3
www.aa.washington.edu

http://www.izmiran.rssi.ru/magnetism/Petrov/dolgino_rep.html

http://www.georentals.co.uk/TR120-new.PDF

http://www.sp.ph.ic.ac.uk/~balogh/spinstr.htm

http://www.magnetometer.com/attcntrl.htm#rad

Reference List

Kedrick Black

slide4
www.goodrich.com

http://www.lund.irf.se/HeliosHome/geomag_magnetometers.html

http://www.sp.ph.ic.ac.uk/~balogh/spinstr.htm

http://server4.oersted.dtu.dk/research/CSC/publica/Papers/Magcalibchamp_PB.PDF

server4.oersted.dtu.dk/research/ CSC/publica/Papers/ESASP_Acalib.PDF

To Explore Further

(Web Pointers)

Kedrick Black

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Definition:

Attitude is the 3-D rotation between the coordinate system of a known object and that of a sensed portion of its surface. Combinations of the support function of a known object with curvature measurements from a visible surface transform attitude determination into optimization problems that can be solved using standard numerical methods. Previous work using the extended Gaussian image (EGI) defined for convex polyhedra is extended to the domain of smooth, strictly convex objects where the EGI becomes equivalent to the second curvature function. Three-dimensional shape matching using the first curvature function is new. Emphasis is placed on theoretical foundations, algorithm development, and experimental proof-of-concept using real objects and surface data obtained from an existing photometric stereo system

  • Spacecraft attitude systems usually consist of two components:
  • vehicle orientation sensors: e.g. magnetometers, horizon sensors, sun sensors, gyroscopes, and star trackers; and
  • - active attitude control actuators: e.g. control momentum gyros, reaction wheels, offset thrusters, and magnetic torque rods.

Kedrick Black

magnetometer
Instrument for measuring the strength and sometimes the direction of magnetic fields, including those on or near the Earth and in space. Magnetometers are also used to calibrate electromagnets and permanent magnets and to determine the magnetization of materials.Magnetometer

Kedrick Black

slide7
Magnetometer measures the magnetic field it is applied to. The magnetometer outputs three magnitudes: X, Y and Z. From these three values you can construct the magnetic field vector (magnitude and direction): B= [X, Y, Z].

How Magnetometers Work

Kedrick Black

types of magnetometers
Proton Magnetometers: A coil surrounds a working sample which is usually a hydrogen containing liquid. The liquid contains protons which have a known gyromagnetic ratio of 2.67515341x10^8 radians/sec/Tesla. The surrounding magnetic field can be calculated within .004nT. Preferred application: Where the absolute accuracy of the magnetometer is important and the low cycling rate will not be a problem.

Overhauser Magnetometers: The Overhauser magnetometer can be likened to a laser or maser. A high frequency RF signal provides the pumping energy to keep the protons constantly processing. A tuned circuit built around the sensing coil functions much like the cavity in a maser. Because of the physical nature of the proton this error in field strength measurement will be less than approximately 25nT. Preferred application: Where the faster sampling rate is important, the absolute accuracy of the free precession magnetometer is not needed.

Optically Pumped Magnetometers: All of the optically pumped magnetometers use the properties of the electron to make their measurements. Light at a particular wave length is radiated through a gas cell containing the working gas of the magnetometer and from there onto a photocell. A small coil, called the H1 coil, applies a small RF field to this gas cell. Preferred application: Where one time adjustment and calibration is needed.

Fluxgate Magnetometer: consists of three sensors, each of which, together with the sensor-specific electronics, provides a voltage proportional to the value of the component of the magnetic field along its axis. The magnetic field vector is measured by an orthogonal arrangement of three sensors. Preferred application: Space where low power and mass are needed.

Vector Helium Magnetometer: based on the response of an optically pumped metastable He population (contained in a glass cell) in the presence of external magnetic fields. Such fields are detected by measuring the transmission of infrared light through the He cell; the transmission coefficient is proportional to the component of the external magnetic field along the optical axis of the He cell. Preferred application: Space where mass and power are not an issue and greater sensitivity and low noise are needed.

Types of Magnetometers

Kedrick Black

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Real Time Monitoring of

The Earths Magnetic Field

Credit: http://geomag.usgs.gov/

Kedrick Black

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How the Magnetometer Works

In Space

At a given point in space and time we can calculate the magnetic field from a model (IGRF2000). By comparing the field direction the magnetometer is telling us with the model we can determine how the magnetometer must be aligned to the field direction to give those X, Y and Z results.

Kedrick Black

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First Magnetometer for

Space research

  • Tested and Flown of Sputnik
  • First successful data collected in 1958

Credit: http://www.izmiran.rssi.ru/magnetism/Petrov/dolgino_rep.html

Kedrick Black

the ideal magnetometer for space
The ideal Magnetometer for space
  • Small
  • Cheap
  • Light
  • Low power
  • Insensitive to noise
  • High Resolution
  • Large temperature range
  • Sustainable to high shocks

Kedrick Black

example placement on a satellite
Example Placement on a satellite

Credit: Department of Aeronautics & Astronautics University of Washington

Kedrick Black

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Calibration of the Magnetometer

Bcal t = I +S Bmeas t) +b = A(t)Bmodel (1)

where,

I = Identity matrix

S = Scaling and orthogonality matrix

b = Bias (offset) vector

A = Attitude rotation matrix

Magnetometer calibration improvement

Credit: http://staff.ee.sun.ac.za/whsteyn/Papers/Magsat.pdf

Kedrick Black

testing
Testing
  • An electric circuit can be connected to the magnetometer which is connected to a microprocessor which is connected a PC.
  • The values the magnetometer are measured and it is rotated and the process is repeated

Kedrick Black

university of washington testing
University of Washington Testing
  • The magnetometer was placed on a board in a way so that the magnetometer’s x-value was pointing straight up and we rotated the magnetometer in the Y-Z plane.

Credit: Department of Aeronautics & Astronautics University of Washington

Kedrick Black

slide18

U of W Experiment Data

Ideal Data

Actual Data

Credit: Department of Aeronautics & Astronautics University of Washington

Kedrick Black

slide19

A Simple

Fluxgate magnetometer

Credit: http://www.tuc.nrao.edu/~demerson/magnet/magnet.html

Kedrick Black

the tfm100s fluxgate magnetometer
The TFM100S Fluxgate Magnetometer

Credit: http://www.magnetometer.com/attcntrl.htm#rad

Kedrick Black

honeywell 3 axis magnetometer hmc2003
Honeywell 3- Axis MagnetometerHMC2003

Credit: www.honeywell.com

Kedrick Black

limitations
High Power Consumption

Low Sensitivity

Large Mass

Susceptible to other magnetic disturbances

Fluxgate is only type easily available for space use

Limitations

Kedrick Black

places to buy cost
Honeywell

Goodrich

Structure Probe Inc.

LessEMF.com

Cost aprox. $5000.00

Places to buy/Cost

Kedrick Black