# US 2013/0154620 A1 · Displacement tamper sensor and method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0154620 A1 - Document ID: US20130154620A1 - Status: Published application - Kind: A1 - Application number: 13/463,591 - Filed: 2012-05-03 - Published: 2013-06-20 - Earliest claimed: 2011-12-19 - Assignees: Tyco Safety Products Canada Ltd. - Inventors: Andrei Bucsa; Stephen D.W. Fosty - Web page: https://patentgrep.com/patent/US20130154620A1 ## CPC - G01R 23/02: Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage - G01R 19/00: Arrangements for measuring currents or voltages or for indicating presence or sign thereof (G01R5/00 takes precedence; for measuring bioelectric currents or voltages A61B5/24) - G06F 17/00: Digital computing or data processing equipment or methods, specially adapted for specific functions (information retrieval, database structures or file system structures therefor G06F16/00) - H02H 3/087: for DC applications - H02J 7/865: {Battery or charger load switching, e.g. concurrent charging and load supply (H02J7/50 takes precedence)} - F16H 59/105: {consisting of electrical switches or sensors} - G01B 7/003: {for measuring position, not involving coordinate determination (coordinate measuring G01B7/004)} - G01B 7/14: for measuring distance or clearance between spaced objects or spaced apertures (G01B7/30 takes precedence) - G01D 5/2457: {Incremental encoders having reference marks} - H02H 3/06: with automatic reconnection - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - F16H: GEARING - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR ## Abstract A displacement sensor for sensing displacement of a first surface relative to a second surface includes a coil mounted on the first surface, and encircling a region in plane; and a conductor extending lengthwise from the second surface through the region. The conductor has a volume that varies along its length. An AC source drives the coil to generate a magnetic field that pierces the region and induces eddy currents in the conductor. Eddy current losses resulting from the eddy currents vary in dependence on the volume of the conductor above and beneath the plane. A sensing circuit is coupled to the AC source to detect changes in eddy current losses, and thereby displacement. Detection of displacement may be used to signal tamper/intrusion. The sensor may further include a visual or audible output to signal such displacement. ## Claims ### Claim 1 A displacement sensor for sensing displacement of a first surface relative to a second surface, said displacement sensor comprising a coil mounted on said first surface, and encircling a region in plane; a conductor extending lengthwise from said second surface through said region, said conductor having a volume that varies along its length; an AC source to drive said coil to generate a magnetic field that pierces said region and induces eddy currents in said conductor, and whereby eddy current losses resulting from said eddy currents vary in dependence on the volume of said conductor above and beneath said plane; a sensing circuit coupled to said AC source to detect changes in eddy current losses, and thereby displacement. ### Claim 2 (depends on 1) The displacement sensor of claim 1, wherein said conductor comprises a frustro-conical portion. ### Claim 3 (depends on 1) The displacement sensor of claim 1, wherein said conductor comprises a bolt having frustro-conical head. ### Claim 4 (depends on 1) The displacement sensor of claim 1, wherein said AC source drives said coil at a frequency between about 1 kHz and 1 MHz. ### Claim 5 (depends on 1) The displacement sensor of claim 1, further comprising a gasket, and wherein said coil is mounted to said gasket. ### Claim 6 (depends on 5) The displacement sensor of claim 5, wherein said gasket is formed of at least one of rubber, silicone, plastic, Textolite, Teflon, paper, or other insulating material. ### Claim 7 (depends on 6) The displacement sensor of claim 6, wherein said AC source and said sensing circuit are mounted to said gasket. ### Claim 8 (depends on 5) The displacement sensor of claim 5, wherein said gasket is mounted to a cabinet. ### Claim 9 (depends on 1) The displacement sensor of claim 1, wherein said AC source comprises a transistor oscillator. ### Claim 10 (depends on 1) The displacement sensor of claim 1, wherein said sensing circuit further comprises an audible or visible output for signaling displacement. ### Claim 11 A method of sensing displacement of a first surface relative to a second surface, said method comprising mounting a coil mounted on said first surface, encircling a region in plane; providing a conductor having a volume that varies along its length, extending from said second surface through said region, said conductor; driving said coil to generate a time varying magnetic field that pierces said region and induces eddy currents in said conductor, and whereby eddy current losses resulting from said eddy currents vary in dependence on the volume of said conductor above and beneath said plane; detecting changes in eddy current losses resulting from said driving to detect displacement. ### Claim 12 (depends on 11) The method of claim 11, further comprising signaling a tamper condition in response to sensing displacement of said first surface relative to said second surface.