Electricity: measuring and testing – Electrostatic field – Using modulation-type electrometer
Reexamination Certificate
2000-04-18
2003-05-13
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Electrostatic field
Using modulation-type electrometer
C324S463000
Reexamination Certificate
active
06563319
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a device and a method for detecting Electrostatic Discharges (ESD) and transient signals and for protecting an electronics device from electromagnetic interference associated with the electrostatic discharges and the transient signals.
An electrostatic discharge (ESD) can permanently damage sensitive electronic devices. For example, semiconductor wafers, magnetic heads for disk drives, integrated circuits, other electronic components and circuits, etc. may be damaged by ESDs. For devices that are not damaged by the ESD, it can still disrupt the operation of an electronic circuit. In non-electronic applications, such as powder handling, etc., ESD can be the cause of a fire.
Short transient spike-like signals resulting from ESD events, commutation of electric motors, solenoids, etc. and other sources can also induce damage into electronics devices and cause circuit malfunctions. Surge protectors are commonly used on power lines, however they cannot protect against common-mode surges. In addition, improperly done ground wires do not provide any protection and can also be a conduit for transmitting surges as well.
Presently, the most common method of reducing damages caused by ESD is preventive measures, such as grounding wrist-wraps, conductive chairs, conductive floor coating, ionizers, etc. All of these preventive measures are supposed to reduce or eliminate the build-up of static voltage that causes the discharges. However, the ultimate indication of the effectiveness of the ESD-preventive measures is the lack of an actual occurrence of electrostatic discharges (also known as ESD events). The detection of ESD events, the measurement of the magnitude of the ESD events, and data logging the data associated with the ESD events for future analysis presents valuable information for assessment of the ESD environment, of the ESD protection, of the real-time addressing of the ESD problems, for determining most likely defects due to ESD, and for statistical process analysis. Thus, it is desirable to provide a device for providing the above functions.
The ESD Event detection devices available today, such as Sanki (U.S. Pat. No. 4,631,473) and Lucent's T100 device provide an indication when an ESD event has exceeded a pre-set level. However, these devices merely detect that the ESD Event has occurred without the ability to measure the magnitude of the ESD Event. The knowledge of the magnitude of the ESD Event, however, provides valuable information that is pertinent to the assessment of the potential damage caused by ESD and also the effectiveness of the ESD-preventive measures. In addition, existing devices are geared towards occasional ESD checks, rather than day-to-day ESD monitoring. A device that offers continuous ESD monitoring will offer real-time indication of ESD problems and provides immediate feedback for implementation of ESD-corrective and preventive measures. It is desirable to provide such an ESD monitoring device.
ESD events or surges in wires and cables last for a very short period of time (typically, nanoseconds). This makes it very difficult to provide measurements of the magnitude of the ESD events in a practical cost-effective and user-friendly manner. Often, a high-speed oscilloscope and an antenna are used to capture the waveform of an ESD Event for analysis of its magnitude. This is not practical for everyday use. Thus, it is desirable to provide a device that can measure the ESD events in wires and cables. Thus, it is desirable to provide an ESD and transient signal monitoring system and method that overcomes the above limitation of typical devices and provides the desirable features described above and it is to this end that the invention is directed.
SUMMARY OF INVENTION
A method and the implementation of improved accuracy of the measurement of an ESD event are described. The ESD event monitoring system in accordance with the invention may accurately measure the magnitude of an ESD event signal by receiving the short-duration pulse or surge from the ESD event and causing a longer duration oscillating secondary signal to be generated based on the short-duration pulse. The oscillatory signal may be more easily measured and the magnitude of the oscillatory signal is proportional to the magnitude of the ESD event so that the magnitude of the ESD event may be accurately determined.
Thus, in accordance with the invention, a device for detecting and measuring short pulse-type signals such as ESD Events and surges is provided. The device receives a signal and converts the electromagnetic field into an electric signal. The device then filters the electric signal in order to reject signals with predetermined properties not associated with short transient-type signals and pass only signals with properties associated with short transient-type signals. Finally, the device measures the signal to provide an analog or digital representation of the magnitude of the received filtered signal. In accordance with the invention, the device includes a resonance means that creates, from a short duration received signal, a new secondary self-resonating signal with longer duration having a magnitude that is a function of the magnitude of the received signal, wherein a slower input signals will not create strong secondary resonance signal and will not be measured.
In accordance with another aspect of the invention, a power supply isolation apparatus is provided wherein the apparatus comprises a first switching means that connects a first storage means to the output of a power source and a second switching means that connect said first storage means to a second storage means. The apparatus further comprises the second storage means being connected to the electric load wherein both of the switching means connect the first storage means alternatively to either said power source or to said second storage means in non-overlapping manner so that said first storage means charges from said power supply and discharges into said second storage means in a manner where said second storage means and said electric load are never directly connected to said power supply and no interference signal is passed from said power supply.
REFERENCES:
patent: 5463379 (1995-10-01), Campbell
patent: 5923160 (1999-07-01), DeChiaro
patent: 6112246 (2000-08-01), Horbal
patent: 6175238 (2001-01-01), Lin
Credence Technologies, Inc.
Cuneo Kamand
Gray Cary Ware & Freidenrich LLP
Nguyen Trung
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