US4679111A — Resistance to ground checker

Claim 1

Independent Claim 141 words

A circuit arrangement for checking resistance to ground of a normally ungrounded coil of a motor comprising: a source of a low-level d.c. voltage, said source having first and second output terminals between which the d.c. voltage is established; means for establishing a conductive connection between said first output terminal and the motor coil; grounding means for connection to a point at ground potential relative to the motor coil; current responsive means connected between said grounding means and said second output terminal of said source for producing an output signal proportional to the amplitude of current flow between said second terminal and said grounding means when said grounding means are connected to the point at ground potential; and motor control means connected for preventing operation of the motor when the output signal from said current responsive means reaches a selected value.

Claim 2

Dependent Claim 141 words

A circuit arrangement for checking resistance to ground of a normally ungrounded coil of a motor comprising: a source of a low-level d.c. voltage, said source having first and second output terminals between which the d.c. voltage is established; means for establishing a conductive connection between said first output terminal and the motor coil; grounding means for connection to a point at ground potential relative to the motor coil; current responsive means connected between said grounding means and said second output terminal of said source for producing an output signal proportional to the amplitude of current flow between said second terminal and said grounding means when said grounding means are connected to the point at ground potential; and motor control means connected for preventing operation of the motor when the output signal from said current responsive means reaches a selected value.

Claim 3

Dependent Claim 47 words

A circuit arrangement as defined in claim 1 wherein said current responsive means comprise: a differential amplifier having an output and inverting and non-inverting inputs; and an impedance connected between said inputs and in series between said grounding means and said second output terminal of said source.

Claim 4

Dependent Claim 30 words

A circuit arrangement as defined in claim 2 wherein said current responsive means further comprise feedback means connected between said output and one of said inputs of said differential amplifier.

Claim 5

Dependent Claim 33 words

A circuit arrangement as defined in claim 3 wherein said feedback means comprise a resistance connected in parallel with a capacitor, said capacitor having a value selected to filter out 60 Hz current.

Claim 6

Dependent Claim 42 words

A circuit arrangement as defined in claim 2 wherein said impedance comprises a first diode connected to be forward biassed by the d.c. voltage between said output terminals of said source when a ground fault current flows between the coil and ground.

Claim 7

Dependent Claim 21 words

A circuit arrangement as defined in claim 5 further comprising a second diode connected in parallel opposition with said first diode.

Claim 8

Dependent Claim 42 words

A circuit arrangement as defined in claim 1 further comprising voltage limiting means connected to said source for limiting the voltage across said output terminals to a selected value when a current is flowing between said second terminal and said grounding means.

Claim 9

Dependent Claim 27 words

A circuit arrangement as defined in claim 7 wherein said voltage limiting means comprise at least one Zener diode connected between said output terminals of said source.

Claim 10

Dependent Claim 28 words

A circuit arrangement as defined in claim 8 wherein said at least one Zener diode is composed of two Zener diodes connected in series in a back-to-back connection.

Claim 11

Dependent Claim 44 words

A circuit arrangement as defined in claim 1 wherein said means for establishing a conductive connection comprise high voltage isolation means connected to said first output terminal and via which the conductive connection is established between said first output terminal and the motor coil.

Claim 12

Dependent Claim 15 words

A circuit arrangement as defined in claim 10 wherein said isolation means comprise an inductor.

Claim 13

Dependent Claim 46 words

A circuit arrangement as defined in claim 7 wherein said voltage limiting means are constructed for causing the selected value to which the voltage across said output terminals is limited to be at least equal to the voltage established across said output terminals by said source.

Claim 14

Dependent Claim 21 words

A circuit arrangement as defined in claim 2 wherein said impedance is conductively connected to said inputs of said differential amplifier.

Claim 15

Dependent Claim 145 words

In combination: a motor having at least one normally ungrounded coil; and a circuit arrangement for checking the resistance to ground of said normally ungrounded coil, said circuit arrangement comprising: a source of a low-level d.c. voltage, said source being independent of said motor and having first and second output terminals between which the d.c. voltage is established; means for establishing a conductive connection between said first output terminal and said coil; grounding means connected to a point at ground potential relative to said coil; current responsive means connected between said grounding means and said second output terminal of said source for producing an output signal proportional to the amplitude of current flow between said second terminal and said grounding means; and motor control means connected for receiving the output signal and preventing operation of said motor when the output signal reaches a selected value.

Claim 16

Dependent Claim 145 words

In combination: a motor having at least one normally ungrounded coil; and a circuit arrangement for checking the resistance to ground of said normally ungrounded coil, said circuit arrangement comprising: a source of a low-level d.c. voltage, said source being independent of said motor and having first and second output terminals between which the d.c. voltage is established; means for establishing a conductive connection between said first output terminal and said coil; grounding means connected to a point at ground potential relative to said coil; current responsive means connected between said grounding means and said second output terminal of said source for producing an output signal proportional to the amplitude of current flow between said second terminal and said grounding means; and motor control means connected for receiving the output signal and preventing operation of said motor when the output signal reaches a selected value.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1990-07-06	1991-01-05	1991-07-07	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1994-07-06	1995-01-05	1995-07-07	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1998-07-06	1999-01-05	1999-07-07	$7700.00	Window Closed / Lapsed

Resistance to ground checker

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