Current status circuit for a variable frequency motor

• US 5,705,989 A
• Filed: 07/19/1996
• Issued: 01/06/1998
• Est. Priority Date: 07/19/1996
• Status: Expired due to Term

• Current Assignee: Veris Industries LLC (Schneider Electric SE)
• Original Assignee: Veris Industries LLC (Schneider Electric SE)
• Inventors: Holce, Kent J., Cota, Roger S.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): GOINS, DAVETTA WOODS
• Application Number:
  US08/684,465
• Time in Patent Office: 536 Days
• Field of Search: 340/660, 340/648, 340/669, 340/658, 364/578, 364/495, 361/84, 361/774, 361/76.39, 324/111, 324/220, 324/127, 342/119, 342/129
• US Class Current: 340/660
• CPC Class Codes: G01R 19/15 Indicating the presence of current

Abstract

A sensor linked with a power cable to produce a first signal in response to the presence of at least one of a sensed current and a sensed voltage within the power cable. The measuring circuit is electrically connected to the sensor to produce a second signal in response to the first signal representative of the magnitude of at least one of the sensed current and the sensed voltage within the power cable. The measuring circuit also produces a third signal in response to the first signal representative of a sensed frequency of at least one of the sensed current and the sensed voltage within the power cable. The measuring circuit includes a model of a set of predetermined relationships between a plurality of reference frequencies and a reference amplitude for each of the reference frequencies for at least one of the sensed voltage and the sensed current of the power cable. The measuring circuit compares the second signal and the third signal to the model to produce a resultant signal indicative of an alarm condition. By including the frequency of the sensed signal in the determination of whether the motor is operating properly, accurate determination of alarm conditions can be made.

Claims

1. A measuring system comprising:

(a) a sensor linked with a power cable to produce a first signal in response to the presence of at least one of a sensed current and a sensed voltage within said power cable;

(b) a measuring circuit electrically connected to said sensor to produce a second signal in response to said first signal representative of the magnitude of at least one of said sensed current and said sensed voltage within said power cable, and produce a third signal in response to said first signal representative of a sensed frequency of at least one of said sensed current and said sensed voltage within said power cable;

(c) said measuring circuit including a model of predetermined relationships between a plurality of reference frequencies and a reference amplitude for each of said reference frequencies for at least one of said sensed voltage and said sensed current of said power cable; and

(d) wherein said measuring circuit compares said second signal and said third signal to said model to produce a resultant signal indicative of an alarm condition.

2. The measuring system of claim 1 wherein said sensor includes a transformer magnetically linked with said power cable to produce said first signal in response to the presence of said sensed current within said power cable.

3. The measuring system of claim 1 wherein said sensor includes an electrical conductor electrically attached to said power cable to produce said first signal in response to said sensed voltage within said power cable.

4. The measuring system of claim 1 wherein said model includes a plurality of frequency bands and an associated amplitude value for each of said frequency bands.

5. The measuring system of claim 4 wherein each of said associated amplitude values for said model is determined during operation of said measuring system.

6. The measuring system of claim 5 wherein each of said associated amplitude values for said model is changed during operation of said measuring system according to the following criteria:

(a) if said resultant signal is indicative of an alarm condition then said associated amplitude value is not changed;

(b) said associated amplitude value is updated with said second signal if said second signal is greater than a respective one of said associated amplitude values; and

(c) said associated amplitude value is updated with said second signal if said second signal is less than said respective one of said associated amplitude values by at least a predetermined percentage thereof.

7. A measuring system comprising:

(a) a sensor linked with a power cable to produce a first signal in response to the presence of at least one of a sensed current and a sensed voltage within said power cable;

(b) a measuring circuit electrically connected to said sensor to produce a second signal in response to said first signal representative of the magnitude of at least one of said sensed current and said sensed voltage within said power cable, and produce a third signal in response to said first signal representative of a sensed frequency of at least one of said sensed current and said sensed voltage within said power cable;

(c) said measuring circuit including a model of predetermined relationships between a plurality of reference frequencies and a reference amplitude for each of said reference frequencies for at least one of said sensed voltage and said sensed current of said power cable;

(d) said model including a plurality of frequency bands and an associated amplitude value for each of said frequency bands;

(e) each of said associated amplitude values for said model being determined during operation of said measuring system;

(f) each of said associated amplitude values for said model being changed during operation of said measuring system according to the following criteria;

(i) if said resultant signal is indicative of an alarm condition then said associated amplitude value is not changed;

(ii) said associated amplitude value is updated with said second signal if said second signal is greater than a respective one of said associated amplitude values;

(iii) said associated amplitude value is updated with said second signal if said second signal is less than a predetermined percentage change of said respective one of said associated amplitude values; and

(g) wherein said measuring circuit compares said second signal and said third signal to said model to produce a resultant signal indicative of an alarm condition.