Expandable electronic protection system

• US 4,075,674 A
• Filed: 12/05/1975
• Issued: 02/21/1978
• Est. Priority Date: 12/18/1972
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Obenhaus, Robert E., Squiers, David J.
• Primary Examiner(s): Moose, Jr., Harry E.
• Application Number:
  US05/637,912
• Time in Patent Office: 809 Days
• Field of Search: 317/13 C, 317/13 R, 317/41, 317/14 J, 361/27, 361/25, 361/37, 361/106
• US Class Current: 361/27
• CPC Class Codes: H02H 3/04 with warning or supervision in addition to disconnection, e.g. for indicating that protective apparatus has functioned watching of pilot wires H02H1/0084; protection of protective arrangements H02H7/008; indication of the state of electronic switches H03K17/18
• CPC Class Codes: H02H 5/042 using temperature dependent resistors

Abstract

The disclosure relates to a protection system for electric motors and the like wherein a plurality of condition responsive PTC impedances are utilized in a bridge circuit to sense predetermined changes in the condition being sensed and proceed to interrupt current flow to a motor or the like being protected. The protection circuit is capable of sensing short circuits or impedances below a predetermined minimum across the sensors to thereby provide an alarm condition also. On the occurrence of the alarm condition, a lockout circuit is energized to prevent application of power to the motor, etc. until after power has been removed from the entire electric circuit and then reapplied thereto. The protection circuit of the present disclosure is also capable of either automatic or manual reset. There is also provided a pop-up flag and remote overload light which can be operated upon sensing of an alarm condition. The pop-up flag is designed to remain in the alarm condition even after removal of the alarm condition and later proper operation when operation is in the manual reset mode.

Claims

1. A protection circuit which comprises,

a. a source of power,

b. a first switch means in series with said source of power,

c. circuit means responsive to an alarm condition to open said first switch means, and

d. lockout means responsive to opening of said switch to maintain said switch open upon removal of said alarm condition, said circuit means includes a second switch means responsive to said alarm condition to open said first switch means and said lockout means includes means responsive to opening of said first switch means to close said second switch means.

2. A protection circuit as set forth in claim 1 further including means for closing said first switch means subsequent to an opening thereof.

3. A protection circuit as set forth in claim 2 wherein said means for closing said switch subsequent to opening thereof includes means for cutting off said source of power.

4. A protection circuit as set forth in claim 1 wherein said second switch means includes a normally nonconducting semiconductor, said lockout means locking said semiconductor into its conducting state upon sensing of said alarm condition.