NCJ Number
50336
Date Published
1978
Length
11 pages
Annotation
A TEST METHOD AND CRITERIA FOR THE INTERPRETATION OF RESULTS ARE PRESENTED FOR EVALUATION OF THE BREAKING CHARACTERISTICS OF METALLIC FOIL USED IN INTRUSION ALARM SYSTEMS TO DETECT GLASS BREAKAGE.
Abstract
THE PROCEDURE HAS BEEN USED TO DETERMINE WHETHER METALLIC FOIL, BONDED TO GLASS IN ACCORDANCE WITH THE MANUFACTURER'S INSTRUCTIONS, WOULD CONSISTENTLY GENERATE AN ALARM SIGNAL WHEN THE GLASS WAS BROKEN. THE EVALUATION OF THE BREAKING CHARACTERISTICS OF THE FOIL REQUIRES THE FOLLOWING TEST EQUIPMENT: (1) GLASS PANELS; (2) A GLASS CUTTER EQUIPPED WITH A TUNGSTEN CARBIDE WHEEL; AND (3) A BREAK FIXTURE CONSISTING OF TWO FLAT PLATFORMS MOUNTED ON A COMMON BASE, ONE HIGHER THAN THE OTHER, TO FORM A BREAKING EDGE. SAMPLE PREPARATION INVOLVES USING THE GLASS CUTTER TO SCRIBE A LINE ACROSS THE WIDTH OF EACH GLASS PANEL AND THE APPLICATION OF FIVE TEST STRIPS OF FOIL PERPENDICULAR TO THE SCRIBE LINE. THE BREAKING PROCEDURE ENTAILS CENTERING THE TEST PANEL ON THE BREAK FIXTURE SO THAT THE SCRIBE LINE AND THE BREAK EDGE ARE ALIGNED, AND THEN APPLYING SUFFICIENT HAND PRESSURE TO THE OVERHANGING PORTION OF THE PANEL IN ORDER TO CAUSE A SWIFT, CLEAN BREAK AT THE SCRIBE LINE. AN OHMETER IS THEN USED TO TEST THE RELATIVE CONDUCTIVITY OF EACH STRIP OF FOIL; EACH TEST STRIP THAT HAS A RESISTANCE GREATER THAN 100 KILOHMS SHOULD BE CONSIDERED BROKEN. A PARTICULAR MAKE OF FOIL IS CONSIDERED TO BE SUITABLE FOR ALARM USE IF A MINIMUM OF 17 TO 20 STRIPS HAVE BEEN TESTED AND FOUND WITHIN THE 100+ KILOHM RANGE. ILLUSTRATIONS OF THE TEST EQUIPMENT AND PROCEDURE ARE PROVIDED.