1. Field of the Invention
The present invention pertains to improved electrical circuits for detecting perceived changes in magnetic fields and which include one or more Hall effect devices in circuit with a magnetic coil.
2. Background
The above-referenced patent application, which is incorporated herein by reference, describes a unique circuit wherein a magnetic coil and a Hall effect device are exposed to a magnetic field and are in circuit with each other to provide an amplified output signal. Such a device is advantageously used in detecting perceived changes in a magnetic field such as sensing cracks and other magnetic anomalies in structures. However, the combination of a magnetic coil, which is capable of generating an output current in response to a change in a magnetic field, in circuit with a Hall effect device, which is exposed to the same changing magnetic field, and further in combination with an integrating circuit is capable of being utilized in other applications wherein relatively low intensity magnetic fields are required to be sensed. For example, a circuit including multiple Hall effect devices with a magnetic coil and an integrator circuit provides a useful switch circuit thanks to the high amplification characteristics of the combination of the coil and the multiple Hall effect devices. The gain of such a circuit is particularly advantageous for applications such as in conjunction with proximity sensing devices and magnetic domain systems. Certain other applications which present problems for prior art magnetic field sensing circuits include fast and slow changing magnetic fields or changing magnetic fields imposed on substantially constant magnetic fields. These applications also find solutions by the use of certain ones of the circuits of the present invention.