Extended minimum dwell shock sensor

• US 5,212,357 A
• Filed: 08/14/1991
• Issued: 05/18/1993
• Est. Priority Date: 08/14/1991
• Status: Expired due to Term

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Hamlin, Inc. (Littelfuse Incorporated)
• Inventors: Reneau, Daniel R.
• Primary Examiner(s): SCOTT, JAMES R
• Application Number:
  US07/745,205
• Time in Patent Office: 643 Days
• Field of Search: 200/61.45 R, 200/61.45 M, 200/61.53, 335/205, 335/206
• US Class Current: 200/61.45M
• CPC Class Codes: H01H 35/147 the switch being of the reed switch type

Abstract

A shock sensor achieving the advantages of extended minimum dwell and extended total dwell employs a reed switch in a housing mounted coaxial to the reed switch. The shock sensor employs a magnet of cylindrical shape, which is coaxial with the reed switch and slidably mounted to activate the reed switch. The shape of the activation magnet, which also serves as an acceleration detecting mass, is that of a cylindrical shell which extends along the axis of the reed switch. The shell has a ring portion extending radially inward and of short axial extent on the end of the magnet which lags in activation. A spring extends between an abutment and the magnet within the shell. When the shock sensor is subjected to an acceleration, the magnet is moved by the acceleration force from a non-activating position. Further extending the activation dwell time of the sensor and, in addition, providing an extended minimum dwell time, is the shape of the magnetic field created by the ring at the first abutting end of the magnet.

Claims

1. A shock sensor comprising:

a) a housing having a first abutment and a second abutment spaced a fixed distance from the first abutment;

b) an activation magnet slidably mounted on the housing and having a first portion adapted to engage against the first abutment and a second portion adapted to engage against the second abutment, wherein the first portion has a greater magnetic flux than the second portion;

c) a reed switch mounted to the housing to be responsive to the position of the activation magnet and coaxial with the magnet such hat the reed switch is activated when the magnet travels to a pre-selected activation position during movement of the magnet in response to an initial acceleration force applied to the sensor;

d) a means for biasing the magnet such that the first portion engages against the first abutment and the reed switch remains unactivated until the housing is subjected to a pre-selected level of acceleration, such that a pre-selected level of acceleration will cause the magnet to slide on the housing past the pre-selected activation position to activate the reed switch.

2. The shock sensor of claim 1 wherein the activation magnet second portion comprises a cylindrical shell with portions defining an interior cylindrical cavity of a first diameter and the first portion comprises a cylindrical ring which is fixed to the shell and has portions defining a second interior cavity of a diameter which is less than the first diameter.

3. The shock sensor of claim 2 further comprising a nonmagnetic cylindrical component located within the shell interior cavity and having portions defining an interior cylindrical cavity coaxial with the second interior cavity and of substantially the same diameter as the second interior cavity.

4. The shock sensor of claim 1 wherein the activation magnet first portion comprises an annular ring of magnetic material, and the activation magnet second portion comprises a cylinder of nonmagnetic material.

5. The shock sensor of claim 1 wherein the activation magnet is a cylinder of constant exterior diameter and having portions defining an interior cylindrical cavity of constant interior diameter and the first portion comprises material of greater magnetic intensity than the material of the second portion.

6. A shock sensor comprising:

a) a housing;

b) an activation magnet slidably mounted to the housing, the magnet having a cylindrical shell portion with portions defining an interior cylindrical cavity of a first diameter and the magnet having a cylindrical ring portion integral with the shell portion and having portions defining a second interior cylindrical cavity coaxial with the shell interior cylindrical cavity and of a diameter which is less than the first diameter;

c) a reed switch mounted on the housing to be responsive to the position of the activation magnet and coaxial with the magnet such that the reed switch is activated when the magnet travels to a pre-selected activation position during movement of the magnet in response to an initial acceleration force applied to the housing; and

d) a means for biasing the magnet in an unactivated position until the housing is subjected to a pre-selected level of acceleration, such that a pre-selected level of acceleration will cause the magnet to slide on the housing past the pre-selected activation position to activate the reed switch.

7. The shock sensor of claim 6 further comprising a nonmagnetic cylindrical component located within the shell interior cavity and having portions defining an interior cylindrical cavity coaxial with the second interior cavity and of substantially the same diameter as the second interior cavity.

8. The shock sensor of claim 6 further comprising:

a) a first abutment located on the housing and a second abutment located on the housing and spaced a fixed distance from the first abutment; and

b) portions of the cylindrical shell opposite the ring portion of the magnet which define a rounded profile, and wherein the biasing means comprises a spring extending between the second abutment and the ring portion, the rounded profile adapted to direct the spring into the shell interior cavity as the magnet moves from a position adjacent the first abutment to a position adjacent the second abutment.

9. The shock sensor of claim 8 wherein the magnet shell interior cavity is dimensioned to enclose the spring when the magnet engages against the second abutment.

10. The shock sensor of claim 6 wherein the housing has a first abutment and a second abutment spaced a fixed distance from the first abutment, and wherein the biasing means comprises a spring extending between the second abutment and the ring portion of the magnet, wherein the spring biases the magnet against the first abutment when the housing is not subjected to a pre-selected level of acceleration, and wherein the spring extends within the shell portion interior cylindrical cavity.

11. The shock sensor of claim 6 wherein the activation magnetic comprises a polymeric host material having magnetic particles suspended therein.

12. A shock sensor comprising:

a) a housing;

b) a cylindrical nonmagnetic carriage having an axial length and having portions defining a cylindrical interior cavity;

c) an annular activation magnet having an axial length less than the carriage axial length and the activation magnet is fixed to the carriage and has portions defining an interior opening which is coaxial with the carriage interior cavity;

d) a reed switch mounted on the housing to be responsive to the position of the activation magnet and coaxial with the magnet such that the reed switch is activated when the magnet travels to a pre-selected activation position during movement of the carriage in response to an initial acceleration force applied to the housing; and

e) a means for biasing the magnet such that the magnet in a position which does not activate the reed switch when the acceleration force applied to the housing is less than a pre-selected amount.

13. The shock sensor of claim 12 wherein the housing has a first abutment and a second abutment spaced a fixed distance from the first abutment, and wherein the biasing means comprises a spring extending between the first abutment and the activation magnet, and wherein the spring biases the magnet against the second abutment when the sensor housing is not subjected to a pre-selected level of acceleration, and wherein the spring extends within the cylindrical interior cavity of the nonmagnetic carriage.

14. The shock sensor of claim 12 wherein the activation magnet comprises a polymeric host material having magnetic particles suspended therein.

15. A shock sensor comprising:

a) a housing;

a cylindrical integral activation magnet slidably mounted to the housing, the magnet having a first portion having a magnetic intensity of a certain level and a second portion integrally formed with the first portion and having a greater magnetic intensity;

c) a reed switch mounted on the housing to be responsive to the position of the activation magnet and coaxial with the magnet such hat the reed switch is activated when the magnet travels to a pre-selected activation position during movement of the carriage in response to an initial acceleration force applied to the housing; and

d) a means for biasing the magnet in an unactivated position until the housing is subjected to a pre-selected level of acceleration such that a pre-selected level of acceleration will cause the magnet to slide on the housing past the pre-selected activation position to activate the reed switch.

16. The shock sensor of claim 15 wherein the activation magnet comprises a polymeric host material having magnetic particles suspended therein.