TIME DELAY SWITCH

• US 3,660,792 A
• Filed: 12/16/1970
• Issued: 05/02/1972
• Est. Priority Date: 12/16/1970
• Status: Expired due to Term

• Current Assignee: Edwin H. Strain, Nalini R. Das
• Original Assignee: Edwin H. Strain, Nalini R. Das
• Inventors: Strain, Edwin H., Das, Nalini R.
• Primary Examiner(s): Harris, George
• Assistant Examiner(s): Morgan, Dewitt M.
• Application Number:
  US05/098,496
• Time in Patent Office: 503 Days
• Field of Search: 337/81,86,87,88,102,103,104,105,106,107,337,338,339,340,341,377
• US Class Current: 337/102
• CPC Class Codes: H01H 61/02 wherein the thermally-sensitive member is heated indirectly, e.g. resistively, inductively

Abstract

A switch which embodies a fail safe feature achieved by means for interrupting the switch circuit when the switch contacts remain closed for longer than a predetermined time period, said switch comprising a support having first and second terminals to one of which a bimetallic element is conductively connected, and third and fourth terminals to which respective ends of a heater element are connected, a conductive strip disposed in normally nonconductive relation to any of the terminals, and a contact member attached to the second terminal, with the bimetallic element and conductive strip being normally spaced out of electrical contact with one another, and with the conductive strip and contact member being normally in electrical contact with one another.

Claims

1. A fail safe switch comprising a support having first and second spaced terminals, a heater element for connection to an external source of heater current, third and fourth terminals on the support and connected to respective ends of the heater element, a bimetallic element adjacent said heater element and connected to said first terminal, a conductive strip adjacent said bimetallic element and mounted on said support in normally nonconductive relation to any of said terminals, and a contact member adjacent said strip and connected to said second terminal, said bimetallic element and conductive strip being normally spaced out of electrical contact with one another, and said conductive strip and contact member being normally in electrical contact with one another.

2. A fail safe switch comprising a casing having first, second, third and fourth spaced electrical terminals, a contact member anchored to said casing and connected to said first terminal, an elongated bimetallic element having one end anchored to the casing and connnected to said second terminal, the opposite end of the bimetallic element extending within the casing toward said contact member and movable along a predetermined path when heated, an elongated flexible conductive strip anchored at one end to the casing in normally nonconductive relation to any of said terminals and with its opposite end disposed normally in electrical contact with said contact member, a midportion of said strip being disposed in the path of movement of the bimetallic element and normally spaced out of electrical contact therewith, and heating means adjacent said bimetallic element and connected at its respeCtive ends to said third and fourth terminals for initially heating the element to cause its movement into electrical contact with the conductive strip and for continued subsequent heating of the element to cause it to forcibly flex the conductive strip in a manner to disrupt the electrical contact between the strip and contact member.

3. A switch as set forth in claim 2 wherein said bimetallic member carries a fixed contact on its movable end, and the conductive strip carries two spaced fixed contacts one of which is positioned for engagement by the fixed contact on the bimetallic element and the other being positioned for engagement with said contact member.

4. A switch as set forth in claim 2 wherein said bimetallic element is structured so that it will bend sufficiently to move the conductive strip out of engagement with the contact member at the end of a predetermined time period.