Sprague Electric Company

Grant D Avery

Jacob K Higgs

Two identical integrated circuit (IC) chips are mounted at a pole of a magnet. Each IC chip includes a Hall-element followed by an amplifier. A comparator is connected to the outputs of the IC chips to produce a voltage that is directly related to the difference between the magnetic field strengths at the two IC chips that may be due to a ferromagnetic article that is closer to one IC chip than the other.

Ferromagnetic article detector with dual Hall-sensors

A strong magnet is bonded to a conventional Hall element package. A bias current is introduced at one of the output terminals of the Hall element in the direction to cause a reduction in the magnet-bias-induced output voltage. This output voltage is easily reduced by this means to zero. The resulting Hall-element detector is shrouded by a large magnetic biasing field while presenting a low or zero DC output component upon which the signal voltage will be superimposed.

Hall element with bucking current and magnet biases

A magnet is bonded to a skewed-hysteresis Hall switch in such a position that the magnetic flux, normal to the Hall element, is equal to the average of the magnetic flux required to operate and the magnetic flux required to release the Hall switch. This magnet-Hall-switch assembly is made by initially employing a magnet of much greater strength than needed. The Hall switch is energized and subjected to an oscillating field of zero average value. The on-time to off-time ratio of the magnet-Hall-switch assembly is measured. A demagnetizing field is adjusted to a strength that is directly related to the difference between unity and the Hall switch on-to-off time, and the magnet is then subjected to the adjusted demagnetizing field. These steps are repeated several times. The magnet is thus partially demagnetized to import to the magnet-biased Hall switch a symmetrical hysteresis characteristic. This symmetrical-hysteresis Hall switch is very sensitive and leads to more reliable operation in rotational speed monitoring devices such as speedometers and certain flow meters.

Symmetrical-hysteresis Hall switch

An integrated circuit includes a Hall-element, a voltage regulator, and a threshold detector. DC power is supplied through a pair of terminals that may be connected to a remote DC voltage source. A switchable constant current sink circuit connected across these terminals is turned on and off in response to the two output states of the threshold detector that in turn is responsive to the Hall-element output voltage. Thus the DC current flowing in the two DC supply lines is a predictable large value or small value corresponding to a low and a high magnitude magnetic field at the sensor, even when the supply DC voltage changes over a wide range.

Two terminal Hall-sensor

An integrated circuit including a Hall element and a threshold detector is encased in a plastic housing with the plane of the Hall element parallel with a face of the housing, providing a two-state Hall element proximity sensor. A light emitting diode (L.E.D.) is mounted in the housing and is connected to the output of the detector, providing visual indication of the state of the sensor. A kit includes the sensor and a compatible magnet to provide to users of little skill, proximity sensor parts that are easily assembled and made immediately effective in use.

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Loudon, NH, United States of America

Grant D Avery