Current sensing relay

• US 5,872,499 A
• Filed: 10/07/1997
• Issued: 02/16/1999
• Est. Priority Date: 12/02/1994
• Status: Expired due to Fees

• Current Assignee: Peder U. Poulsen
• Original Assignee: Peder U. Poulsen
• Inventors: Poulsen, Peder U.
• Primary Examiner(s): DONOVAN, LINCOLN D
• Application Number:
  US08/946,369
• Time in Patent Office: 497 Days
• Field of Search: 335/78-86, 335/124, 335/128, 335/177-179, 335/182, 361/139, 361/143, 361/160, 361/166
• US Class Current: 335/177
• CPC Class Codes: H01H 3/503 making use of electromagnets

Abstract

An electromagnetic relay, having ON and OFF states, for connecting a source of electrical current to a load, said relay comprising: an armature movable between ON and OFF positions corresponding, respectively, to said ON and OFF states of said relay; a magnetic core surrounded by first windings forming a holding coil to magnetize said core when a first portion of electrical current is passed through said holding coil and consequently to cause said armature to move from said OFF position to said ON position as a result of a magnetic attraction produced between said magnetic core and said armature, resulting in causing a second portion of electrical current to flow through said load; said magnetic core additionally surrounded by second windings forming a load coil through which said second portion of said electrical current flows when said armature is in said ON position, said load coil producing a magnetic field which counteracts a magnetic field produced by said holding coil; and parameters of said load coil being selected such that, when said second portion of said electrical current reaches a predetermined level, a resulting loss in magnetic attraction between said armature and said magnetic core will cause said armature to be released, interrupting flow of said electrical current through said holding coil, and causing said relay to switch from said ON state to said OFF state.

Claims

1. An electromagnetic relay, having ON and OFF states, for connecting a source of electrical current to a load, said relay comprising:

(a) an armature movable between ON and OFF positions corresponding, respectively, to said ON and OFF states of said relay;

(b) a magnetic core surrounded by first windings forming a holding coil to magnetize said core when a first portion of electrical current is passed through said holding coil and consequently to cause said armature to move from said OFF position to said ON position as a result of a magnetic attraction produced between said magnetic core and said armature, resulting in causing a second portion of electrical current to flow through said load;

(c) said magnetic core additionally surrounded by second windings forming a load coil through which said second portion of said electrical current flows when said armature is in said ON position, said load coil producing a magnetic field which counteracts a magnetic field produced by said holding coil; and

(d) parameters of said load coil being selected such that, when said second portion of said electrical current reaches a predetermined level, a resulting loss in magnetic attraction between said armature and said magnetic core will cause said armature to be released, interrupting flow of said electrical current through said holding coil, and causing said relay to switch from said ON state to said OFF state.

2. An electromagnetic relay, as defined in claim 1, further comprising:

attenuation means disposed in series with said holding coil, serving to pre-select strength of said magnetic field produced by said holding coil.

3. An electromagnetic relay, as defined in claim 1, further comprising:

(a) a negative temperature coefficient resistor disposed in series with said load coil;

(b) a shunt resistor disposed in parallel with said load coil and said negative temperature coefficient resistor; and

(c) said shunt resistor being selected to carry a main part of said second portion of electrical current, presence of said negative temperature coefficient resistor resulting in a delayed action due to gradual rise of said second portion of electrical current through said load coil as temperature of said negative temperature coefficient resistor rises, until said magnetic field produced by said load coil increases sufficiently to cause said relay to switch from said ON state to said OFF state.