Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-03-30
2001-10-23
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S127000, C324S529000, C324S263000
Reexamination Certificate
active
06307382
ABSTRACT:
FIELD OF USE
This invention relates to devices and techniques for sensing currents, especially currents that arise in plate structures such as a baseplate structure of a flat-panel cathode-ray tube (“CRT”) display.
BACKGROUND
A flat-panel display is a matrix-addressed flat-panel device typically formed with a baseplate structure and a faceplate structure situated opposite the baseplate structure. In a flat-panel CRT display of the gated field-emission type (“field-emission display”), the baseplate structure contains a generally flat baseplate, a lower level of generally parallel emitter electrodes extending over the interior surface of the baseplate, a dielectric layer overlying the emitter electrodes, and an upper level of control (or gate) electrodes extending over the dielectric layer generally perpendicular to the emitter electrodes. Electron-emissive elements are situated in cavities in the dielectric layer and are exposed through openings in the control electrodes.
During operation of the field-emission display (“FED”), electrons emitted from selected electron-emissive elements move towards the faceplate structure. The electrons strike corresponding light-emissive regions in the faceplate structure and cause them to emit light that produces an image on the exterior surface of a transparent faceplate. Each of the locations at which one of the control electrodes crosses one of the emitter electrodes in the baseplate structure defines a picture element (“pixel”) in a black and white display and a sub-pixel in a color display, three sub-pixels normally forming a color pixel.
Various types of equipment and procedures are employed in testing flat-panel displays to determine how much, if any, current flows in particular parts of the displays. It is generally desirable that testing for current flow be performed rapidly.
Henley, U.S. Pat. No. 5,073,754, describes how a liquid-crystal display (“LCD”) is tested for short circuit defects, and thus for undesirable current flow, utilizing a magnetic sensor of undisclosed configuration. The magnitude of short circuit current increases with the magnitude of the sensed magnetic field. Henley's short circuit detection technique entails scanning the magnetic sensor across parts of the LCD, thereby enabling currents that characterize short circuit defects to be identified quickly. Consequently, magnetic sensing is a promising way of assessing current flow. It is desirable to have equipment that utilizes magnetic sensing in producing data indicative of current flow in flat-panel displays, especially FEDs.
GENERAL DISCLOSURE OF THE INVENTION
The present invention furnishes a device for magnetically sensing current in a generally flat plate structure such as a baseplate structure of a flat-panel CRT display. Two components of the present current-sensing device are a magnetic head and signal processing circuitry. The magnetic head senses changes in current-induced magnetic flux as the head is positioned over the plate structure. The head provides a head output signal indicative of any changes sensed in the magnetic flux. The signal processing circuitry processes the head output signal to produce a data signal indicative of how much, if any, current flows in the plate structure below the head.
The current sensor of the invention preferably includes a location sensor that determines the lateral position of the magnetic head relative to the plate structure and thus determines where current flows laterally in the plate structure. Typically, the location sensor optically senses the topography of the plate structure. For example, the location sensor can be formed with a light source and a light sensor that generates an electrical signal in response to light that is reflected off the plate structure after having been emitted by the light source.
A gas-cushion mechanism is preferably employed in the current sensor to control how high the magnetic head is positioned above the plate structure. The gas-cushion mechanism causes gas to flow between the head and the plate structure, thereby producing a gas cushion that regulates the height of the head above the plate structure. In the preceding way, the current-sensing and current-locating functions are performed without physically intruding on the plate structure.
The present current sensor is typically utilized to rapidly measure current in a primary electrical conductor of a plate structure when the primary conductor is furnished with a time-varying stimulus. In particular, a driving voltage that varies with time in a prescribed manner is applied to the primary conductor as the magnetic head is passed over the conductor. The driving voltage can be applied between different parts of the conductor or between the primary conductor and another electrical conductor nominally electrically insulated from the primary conductor in the plate structure. The expression “nominally electrically insulated” means that the two conductors are substantially electrically insulated from each other except possibly for a short circuit defect that may unintentionally electrically couple the conductors. In either case, the current sensor provides the data signal at a value indicative of any current flowing in the primary conductor.
The driving voltage is typically provided at a selected frequency, normally at least 70 Hz so as to be safely above the 60-Hz and 50-Hz power-line frequencies employed respectively in the United States and Europe. By performing the current sensing operation in this manner, the head output signal normally has a frequency component at the selected frequency. In generating data indicative of how much current flows in the two conductors, the signal processing circuitry in the current sensor can search for the frequency “signature” of the driving voltage. Noise, especially noise resulting from nearby equipment using power supplied at 60 Hz or 50 Hz, is reduced in the resulting current data, thereby improving the accuracy of the current determination. The present invention thus provides a substantial advance.
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Brown Glenn W.
Candescent Technologies Corporation
Hamdan Wasseem H.
Meetin Robert J.
Skjerven Morrill & MacPherson LLP
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