Aparatus and method of determining a reaction sensitivity threshold of materials to elecrostatic discharge
Inventors
Hernandez, David • Hoey, David • Chipuk, Jr., Joseph Eugene • Ostrow, Benjamin
Assignees
US Department of Homeland Security
Publication Number
US-9970879-B2
Publication Date
2018-05-15
Expiration Date
2035-09-23
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Abstract
A method and apparatus for determining the sensitivity to electrostatic discharge (ESD) of energetic and volatile samples. The method and apparatus include an optical detector configured to detect the optical light intensity from an ESD event with time resolution less than 15 microseconds. The optical light intensity is integrated to obtain an integrated light intensity. The method and apparatus further include processing circuitry configured to determine whether the ESD event is a “Go” event, wherein the energetic material undergoes decomposition generating additional light in addition to light generated by the ESD event itself, or the ESD event is a “No-Go” event without decomposition of the energetic/volatile material. The integrated light intensity threshold between “Go” and “No-Go” events is determined using a statistical distribution of inert sample measurements.
Core Innovation
The invention relates to a method and apparatus for determining the sensitivity of energetic and volatile materials to electrostatic discharge (ESD) events. It includes an optical detector configured to detect optical light intensity from ESD events with high time resolution, and processing circuitry configured to determine whether an ESD event triggers a reaction (termed a 'Go' event) indicating decomposition of the material or is a 'No-Go' event without decomposition. The apparatus determines an integrated light intensity threshold between Go and No-Go events based on a statistical distribution of measurements from inert samples.
The invention addresses the problem in conventional ESD sensitivity testing of materials where differentiating between reaction and non-reaction events relies heavily on subjective observation by users. Such subjective assessments are inconsistent, prone to error due to fatigue, distractions, and exposure to ultraviolet light, and can cause physiological damage. Further, existing methods like gas detection and high-speed camera analysis either have limitations related to environmental conditions or still require subjective user input. Thus, there is a need for an objective, consistent, and reproducible method and apparatus to differentiate between reaction and non-reaction events without user input.
The disclosed system uses an optical detection unit such as a high-speed digital camera or photodetector coupled with processing circuitry that calculates a Go/No-Go threshold from inert sample data to statistically classify ESD events as reactions or non-reactions autonomously. The method involves incrementally varying the ESD energy and determining the sensitivity threshold of the sample when a predetermined count of reaction events occurs. The apparatus and method improve safety for testers, increase consistency and reliability of results, and inherently account for the contribution of the testing equipment to the detected reactions.
Claims Coverage
The claims define several inventive features related to an electrostatic discharge sensitivity apparatus and a method for determining ESD sensitivity in samples, focusing on optical detection, triggering, processing, and apparatus configuration.
Optical detection of light intensity data with high time resolution
An optical detector detects light intensity data representative of optical light intensity of an ESD event with a time resolution less than or equal to 20 microseconds.
Trigger generation for time interval determination
A trigger generator creates a trigger signal when the ESD event occurs, determining the time interval over which the optical detector collects light intensity data.
Processing circuitry determining Go/No-Go threshold and counts
Processing circuitry calculates a Go/No-Go threshold from a statistical distribution of light intensity data using an inert sample, determines counts of Go events when intensity exceeds this threshold for real samples, and determines if ESD energy exceeds a sensitivity threshold based on these counts.
Use of high-speed camera with specific frame rate and frame count
The optical detector can be a high-speed camera capable of at least 75,000 frames per second and recording at least 100 consecutive frames, including background frames prior to the event.
Alternative photodetector implementations
The optical detector can alternatively be a photodiode, avalanche photodiode, or photomultiplier tube, optionally coupled with a boxcar integrator that integrates light intensity data within a predetermined time window.
Versatile trigger initiation methods
Trigger signals can be initiated by optical, acoustic, electrical signals from the ESD event, or a manual trigger.
Go/No-Go threshold statistical determination to control false positives
The Go/No-Go threshold is set to maintain false Go events below a predetermined statistical level based on distributions from inert samples.
Apparatus configuration for controlled ESD event initiation
The apparatus includes a storage capacitor electrically connected to a ground plane and a needle, with a needle actuator to adjust needle proximity to the ground plane, ensuring electrical current passes through the sample during ESD.
Method of sample positioning and ESD event initiation
A method positions a sample between a ground plane and needle connected to a storage capacitor, causes a voltage potential difference, adjusts space until an ESD event occurs, and records light intensity with processing to establish Go/No-Go thresholds statistically.
Sequential testing and threshold determination method
The method compares light intensity data of ESD events on energetic samples to Go/No-Go thresholds, determines event classification, adjusts ESD energy incrementally, and repeats testing until the sensitivity threshold is identified.
The claims collectively cover an objective and automated ESD sensitivity testing system that uses precise optical detection and statistical processing to determine reaction thresholds, reducing reliance on subjective observation and improving reliability and safety.
Stated Advantages
Reduces or eliminates subjectivity in determining reaction versus non-reaction events during ESD testing.
Provides consistent and reproducible resolution between Go and No-Go events without user input.
Improves safety for testers by reducing ultraviolet light exposure associated with traditional observation methods.
Enhances reliability and uniformity of test results across different laboratories.
Accounts for the testing equipment's contribution to reaction signals, improving accuracy.
Documented Applications
Small scale safety testing of energetic and volatile materials to objectively differentiate between reaction and non-reaction events.
Use by Government and commercial explosive manufacturers, explosive testing laboratories, and international testing groups to determine material safety for transport.
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