| Cryogenic Hall Generators and Probes | Features
- Low temperature dependence
- Low resistance, low power dissipation
- Low linearity error: -150 kG to +150 kG
- Axial and transverse configurations available
- Small active area
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Attaching Hall Generators to the Model 421, 450, 460, and 475 Gaussmeters |
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| The MCBL-6 cable allows discrete Hall generators to be mated to the Model 421, 450, 460, and 475 gaussmeters. The cable is shipped with a 3½-inch floppy disk containing the Hallcal.exe file to program the cable PROM through the gaussmeter RS-232C port. Because of the many intricacies involved with proper calibration, the user is responsible for the measurement accuracy. |
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| Certain Hall generator sensitivity constraints are applicable: |
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Sensitivities between 5.6 mV/kG and 10.4 mV/kG at 100 mA current. |
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Sensitivities between 0.56 mV/kG and 1.04 mV/kG at 100 mA current. |
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| System Requirements |
- Lake Shore gaussmeter connected via RS-232C to the PC computer
- Hall generator meeting the sensitivities given above
- Calibration or sensitivity constant and serial number of the Hall generator
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Hall Generator Theory |
| A Hall generator is a solid state sensor which provides an output voltage proportional to magnetic flux density. As implied by its name, this device relies on the Hall effect principle. The Hall effect principle is the development of a voltage across a sheet of conductor when current is flowing and the conductor is placed in a magnetic field. |
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| Electrons (the majority carrier most often used in practice) “drift” in the conductor when under the influence of an external driving electric field. When exposed to a magnetic field, these moving charged particles experience a force perpendicular to both the velocity and magnetic field vectors. This force causes the charging of the edges of the conductor, one side positive with respect to the other. This edge charging sets up an electric field which exerts a force on the moving electrons equal and opposite to that caused by the magnetic-field-related Lorentz force. The voltage potential across the width of the conductor is called the Hall voltage. This Hall voltage can be utilized in practice by attaching two electrical contacts to the sides of the conductor. |
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| The Hall voltage can be given by the expression: VH= = γBB sinΦ |
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VH = Hall voltage (mV) |
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γB = Magnetic sensitivity (mV/kG) at a fixed current |
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B = Magnetic field flux density (kG) |
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Φ= Angle between magnetic flux vector and the plane of Hall generator |
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| As can be seen from the formula above, the Hall voltage varies with the angle of the sensed magnetic field, reaching a maximum when the field is perpendicular to the plane of the Hall generator. |
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Using a Hall Generator |
 A Hall generator is a 4-lead device. The control current (I c ) leads are normally attached to a current source such as the Lake Shore Model 120CS. The Model 120CS provides several fixed current values compatible with various Hall generators. The Hall voltage leads may be connected directly to a readout instrument, such as a high impedance voltmeter, or can be attached to electronic circuitry for amplification or conditioning. Device signal levels will be in the range of microvolts to hundreds of millivolts The Hall generator input is not isolated from its output. In fact, impedance levels on the order of the input resistance are all that generally exist between the two ports. To prevent erroneous current paths which can cause large error voltages the current supply must be isolated from the output display or the downstream electronics. |
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Configurations |
| Hall generators come in two main configurations, axial and transverse. Transverse devices are generally thin and rectangular in shape. They are applied successfully in magnetic circuit gaps, surface measurements, and general open field measurements. Axial sensors are mostly cylindrical in shape. Their applications include ring magnet center bore measurements, solenoids, surface field detection, and general field sensing. |
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Active Area |
| The Hall generator assembly contains the sheet of semiconductor material to which the four contacts are made. This is normally called a “Hall plate.” The Hall plate is, in its simplest form, a rectangular shape of fixed length, width, and thickness. Due to the shorting effect of the current supply contacts, most of the sensitivity to magnetic fields is contained in an area approximated by a circle, centered in the Hall plate, with a diameter equal to the plate width. Thus, when the active area is given, the circle as described above is the common estimation. |
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Cryogenic Gaussmeter Probes |
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| Lake Shore offers cryogenic Hall generators mounted into gaussmeter probes, which work in a variety of magnetic measurement applications. Our probes are factory calibrated for accuracy and nterchangeability. Factory-calibrated probes feature a programmable read-only memory (PROM) in the probe connector so that Hall generator calibration data can be read automatically by the Lake Shore gaussmeter. |
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| Lake Shore also offers a complete line of axial, transverse, flexible, tangential, gamma, brass stem, and multi-axis Hall probes. |
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Axial |
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Transverse |
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