Magnetic field sensors are used to measure magnetic flux and/or the strength and direction of a magnetic field. They are used mainly in scientific measurement, navigation, and industrial applications. Magnetic field sensors use several types of sensing technologies. Magnetoresistive devices measure electrical resistance as a function of the applied or ambient magnetic field. Flux gate or coil sensors measure differences in the magnetic field at the ends of a vertical rod and then plot this information on a grid. Hall Effect sensors convert the energy stored in a magnetic field to an electrical signal by developing a voltage between the two edges of a current-carrying conductor whose faces are perpendicular to a magnetic field. Magnetoinductive sensors consist of a coil that surrounds a ferromagnetic core whose permeability changes within the earth's magnetic field. Proton precession devices use liquids such as kerosene and methanol that have high densities of hydrogen atoms. Overhauser or nuclear precession devices combine an electron-rich liquid with hydrogen and subject the mixture to a radio frequency (RF) signal. Optically-pumped sensors polarize a gaseous alkali with a specific wavelength of light. Superconducting quantum interference devices (SQUID) are very sensitive to low magnetic fields.
Selecting magnetic field sensors requires an analysis of performance specifications. Flux density, the total measurement range in gauss (G), often corresponds to the linear output region of the sensing technology. Resolution, another important specification, is the smallest measurable increment. Accuracy is a percentage of full-scale. Bandwidth is the frequency range over which magnetic field sensors meet their accuracy specifications. The number of axes indicates the number of possible, simultaneous measurements for magnetic field sensors. Single-axis devices are common, but two-axis and three-axis devices are also available. Directional magnetic field sensors measure the direction of the magnetic field and may provide bipolar outputs. Magnitude sensors measure the magnitude of the magnetic field. Maximum shock, maximum vibration and operating temperature are additional specifications.
Magnetic field sensors are used to measure magnetic flux and/or the strength and direction of a magnetic field. They are used mainly in scientific measurement, navigation, and industrial applications. Magnetic field sensors use several types of sensing technologies. Magnetoresistive devices measure electrical resistance as a function of the applied or ambient magnetic field. Flux gate or coil sensors measure differences in the magnetic field at the ends of a vertical rod and then plot this information on a grid. Hall Effect sensors convert the energy stored in a magnetic field to an electrical signal by developing a voltage between the two edges of a current-carrying conductor whose faces are perpendicular to a magnetic field. Magnetoinductive sensors consist of a coil that surrounds a ferromagnetic core whose permeability changes within the earth's magnetic field. Proton precession devices use liquids such as kerosene and methanol that have high densities of hydrogen atoms. Overhauser or nuclear precession devices combine an electron-rich liquid with hydrogen and subject the mixture to a radio frequency (RF) signal. Optically-pumped sensors polarize a gaseous alkali with a specific wavelength of light. Superconducting quantum interference devices (SQUID) are very sensitive to low magnetic fields.
Selecting magnetic field sensors requires an analysis of performance specifications. Flux density, the total measurement range in gauss (G), often corresponds to the linear output region of the sensing technology. Resolution, another important specification, is the smallest measurable increment. Accuracy is a percentage of full-scale. Bandwidth is the frequency range over which magnetic field sensors meet their accuracy specifications. The number of axes indicates the number of possible, simultaneous measurements for magnetic field sensors. Single-axis devices are common, but two-axis and three-axis devices are also available. Directional magnetic field sensors measure the direction of the magnetic field and may provide bipolar outputs. Magnitude sensors measure the magnitude of the magnetic field. Maximum shock, maximum vibration and operating temperature are additional specifications.
Magnetic field sensors differ in terms of electrical outputs. Analog current levels such as 4 – 20 mA are suitable for sending signals over long distances. Analog voltages are simple, usually linear functions. Modulated analog output signals are encoded, but still analog in nature. Examples include sine wave, pulse wave, amplitude modulation (AM), and frequency modulation (FM) signals. Several types of serial outputs are available. RS232, RS422, and RS485 are common serial, digital protocols. Popular parallel protocols include the general-purpose interface bus (GPIB), a standard which is also known as IEEE 488. Other digital outputs for magnetic field sensors include transistor-transistor logic (TTL) signals. Outputs that change the state of a switch or alarm are also available.
