Patent
1988-03-18
1989-04-04
Miller, Stanley D.
350331R, 350334, G02F 113
Patent
active
048180726
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of detecting an electric field, particularly a method using a device having a liquid crystal display element, and to a device for detecting an electric field, particularly a device having a liquid crystal display element.
BACKGROUND OF THE INVENTION
It is frequently necessary to determine whether a particular component, line, cable, element, etc., in an electrical circuit is "live," that is, whether it bears a voltage. Such a determination is especially important where the voltage of concern is substantial, for obvious safety reasons. Even where electrical circuits proper are not involved, the ability to detect a voltage may be important. To cite but a few examples: because of the fire hazard represented by sparks, it is often desirable to know if there is an accumulation of static electricity in an object. A piece of equipment associated with an electrical circuit but not part of the circuit itself may need to be tested to determine if it has been properly grounded of if it has been unintentionally electrically connected to the circuit. A capacitor may need to be tested to determine if it is charged. Hereinafter, the generic term "electrical component" will be used to designate not only components, lines, cables, etc. in an electrical circuit proper, but also articles and equipment in which a static or other electrical charge is to be detected.
Preferably, the device for such determinations is rugged, portable, easy to use, reliable, and inexpensive. Ruggedness permits the device to survive adverse use conditions in which it might be subjected to impact, temperature extremes, chemicals, etc. Portability is advantageous because a portable device can monitor a multiplicity of components instead of being permanently or semi-permanently attached to a particular one. For example, where a single electrical system requires non-simultaneous voltage monitoring at several different points, this can be done with a single portable device. An easy-to-use device does not require complex physical or electrical connections to the component being monitored. Preferably, the connections are simple to make and disconnect; more preferably, the device operates remotely--that is, it requires no connections whatsoever. A remote device is also advantageous safety-wise, since the danger of an electric shock in the event of a malfunction or misuse is reduced. The device should be reliable, for a false negative reading can create a severe risk of injury. The economic advantages of an inexpensive device are self-evident. For example, where it is desirable to monitor several points in an electrical system simultaneously, an inexpensive device reduces or minimizes the cost of installing one such device at each point.
Further, while for certain applications the device need only display a qualitative, "on" or "off" indication of voltage, for other applications it is desirable or essential that the device provide a quantitative or semi-quantitative read-out of the voltage being detected.
Liquid crystals have been employed in the display element of many devices, including voltage detecting devices. Such devices rely on the preferential alignment of the long axes of the constituent molecules along one direction, a phenomenon known as molecular anisotropy, and the ability to control this preferential alignment with an applied voltage. The optical properties of such liquid crystals are also anisotropic. For example, along one axis, light may be scattered or absorbed, giving the liquid crystal material an opaque or dark appearance, while along a perpendicular axis, light may be transmitted, giving the liquid crystal material a transparent appearance.
Liquid crystal displays (LCD's) possess numerous advantages which are reflected by their popularity and ascendancy over other types of displays, such as light emitting diodes, or LED's. LCD's are easily fabricated into complex patterns which can be in the form of alphanumeric characters or graphic symbols. A single LCD display can comprise multiple elements wh
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Burkard Herbert G.
Chao Yuan
Gallivan Richard
Miller Stanley D.
Raychem Corporation
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