Marker for locating a buried object

• US 4,873,533 A
• Filed: 10/09/1987
• Issued: 10/10/1989
• Est. Priority Date: 11/18/1986
• Status: Expired due to Fees

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Oike, Tomoyasu
• Primary Examiner(s): Hille, Rolf
• Assistant Examiner(s): Johnson, D.
• Application Number:
  US07/106,343
• Time in Patent Office: 732 Days
• Field of Search: 343/719, 343/744, 340/571, 340/572, 324/329
• US Class Current: 343/744
• CPC Class Codes: F16L 1/11 for the detection or protection of pipes in the ground
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00

Abstract

A marker for positioning near a buried object wherein the marker can be detected to locate the buried object. The marker includes a passive resonant type antenna which becomes inoperative when the initial position for the buried marker is changed. A lead wire and/or a mercury switch that is a part of the antenna serve to make the antenna inoperative due to such change in the initial position of the marker.

Claims

1. A marker for positioning in proximity to a buried object, the marker being detected to locate the buried object by use of the fact that an antenna of the passive resonance type having a coil and capacitor connected in a closed series circuit for operation, which forms a part of the marker, is resonantly responsive to an electromagnetic wave of a specified frequency transmitted to the marker, the marker including means forming a part of the series circuit for opening the series circuit in response to a change, such as inclination and displacement, of the marker from its initial position of installation thereby preventing the occurrence of any resonant response by the marker to an electromagnetic wave transmitted subsequent to the occurrence of such change, said means including a switch which is position sensitive for presenting an electrical open or closure, said switch presenting an electrical open in response to the inclination of the marker from its initial position of installation.

2. A marker according to claim 1 wherein said switch is a mercury switch.

3. A marker for positioning in proximity to a buried object, the marker being detected to locate the buried object by use of the fact that an antenna of the passive resonance type having a coil and capacitor connected in a closed series circuit for operation, which forms a part of the marker, is resonantly responsive to an electromagnetic wave of a specified frequency transmitted to the marker, the marker including means forming a part of the series circuit for opening the series circuit in response to a change, such as inclination and displacement, of the marker from its initial position of installation thereby preventing the occurrence of any resonant response by the marker to an electromagnetic wave transmitted subsequent to the occurrence of such change, said means including a lead wire, formed from a part of the coil, which can be fixedly secured to the buried object whereby said lead wire can be broken to open the series circuit in response to displacement of the marker from its initial position of installation.

4. A marker for positioning in proximity to a buried object, the marker being detected to locate the buried object by use of the fact that an antenna of the passive resonance type having a coil and capacitor connected in a closed series circuit for operation, which forms a part of the marker, is resonantly responsive to an electromagnetic wave of a specified frequency transmitted to the marker, the marker including means forming a part of the series circuit for opening the series circuit in response to a change, such as inclination and displacement, of the marker from its initial position of installation thereby preventing the occurrence of any resonant response by the marker to an electromagnetic wave transmitted subsequent to the occurrence of such change, said means including a switch which is position sensitive for presenting an electrical open or closure, said switch presenting an electrical open in response to the inclination of the marker from its initial position of installation, and a lead wire, formed from a part of the coil, which can be fixedly secured to the buried object whereby said lead wire can be broken to open the series circuit in response to displacement of the marker from its initial position of installation.

5. A marker according to claim 4 wherein said switch is a mercury switch.