Active RFID asset tracking tag with current-sensing cable clamp

• US 10,126,334 B2
• Filed: 05/22/2017
• Issued: 11/13/2018
• Est. Priority Date: 04/16/2014
• Status: Active Grant

• Current Assignee: Emanate Wireless, Inc.
• Original Assignee: Emanate Wireless, Inc.
• Inventors: Sugar, Gary L.
• Primary Examiner(s): Le, Thien M
• Assistant Examiner(s): Habib, Asifa
• Application Number:
  US15/601,223
• Publication Number:
  US 20170254838A1
• Time in Patent Office: 540 Days
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G06K 19/0702 the arrangement including a battery
• CPC Class Codes: G06K 19/0716 at least one of the integrated circuit chips comprising a sensor or an interface to a sensor
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/07758 arrangements for adhering the record carrier to further objects or living beings, functioning as an identification tag

Abstract

Configurations are provided for measuring electrical current flow through an AC power cable to a host device. An enclosure is provided that includes various components, such as components of an active RFID tag. A cable clamp is provided that is configured to attach the enclosure to the AC power cable. The cable clamp includes magnetic sensors that are responsive to electrical current flowing through the AC cable to generate signals indicative of the current flowing through the AC cable.

Claims

1. A method for measuring the electrical current flowing through an electrical power cable to determine power consumption by a power consuming device connected to the electrical power cable, comprising:

affixing a single magnetic field sensor to an outer insulator of the electrical power cable, wherein the outer insulator of the electrical power cable is wrapped around two or more insulated inner conductors carrying electrical current in equal but opposite directions in the electrical power cable;

physically constraining the magnetic field sensor to the outer insulator of the electrical power cable so that it does not change position for a period of time;

obtaining a first plurality of magnetic field strength measurements from the magnetic field sensor while it is physically constrained to the outer insulator of the electrical power cable;

calculating, with a computing device coupled to the single magnetic field sensor, a root mean squared (RMS) value of the first plurality of magnetic field strength measurements; and

deriving, with the computing device, a measure of the electrical current flowing through the electrical power cable based on the RMS of the first plurality of magnetic field strength measurement, wherein deriving includes scaling the RMS value of the first plurality of magnetic field strength measurements by a constant and

computing, with the computing device, the constant during a calibration procedure after the magnetic field sensor is physically constrained to the outer insulator of the electrical power cable by;

supplying an electrical current of a known RMS current level to the electrical power cable;

obtaining a second plurality of magnetic field strength measurements from the magnetic field sensor while the electrical current of the known RMS current level is flowing through the electrical power cable;

calculating an RMS value of the second plurality of magnetic field strength measurements; and

dividing the RMS value of the second plurality of magnetic field strength measurements by the known RMS current level to derive the constant.

2. The method of claim 1, wherein the electrical power cable has a circular cross-section.

3. The method of claim 1, further comprising:

deriving, with the computing device, a measure of power consumption of the power consuming device based on the measure of electrical current flowing through the electrical power cable during operation of the power consuming device.

4. The method of claim 1, wherein the single magnetic field sensor is a single inductive coil.

5. The method of claim 1, wherein the computing device is contained within an RFID tag.

6. The method of claim 1, wherein the computing device is contained within an RFID tag, wherein the RFID tag is connected by a cable to a package that includes the single magnetic sensor.

7. An apparatus to determine power consumption by a power consuming device connected to an electrical power cable comprising:

a single magnetic field sensor configured to be affixed to an outer insulator of the electrical power cable, wherein the outer insulator of the electrical power cable is wrapped around two or more insulated inner conductors carrying electrical current in equal but opposite directions in the electrical power cable;

an analog-to-digital converter coupled to an analog output of the single magnetic field sensor and configured to convert the output to a digital output; and

a processor coupled to the analog-to-digital converter to receive the digital output of the analog-to-digital converter for a first plurality of magnetic field strength measurements from the magnetic field sensor while it is physically constrained to the outer insulator of the electrical power cable, to compute a root mean squared (RMS) value of the first plurality of magnetic field strength measurements and to derive a measure of the electrical current flowing through the electrical power cable based on the RMS of the first plurality of magnetic field strength measurements, wherein the processor is configured to scale the RMS value of the first plurality of magnetic field strength measurements by a constant computed ruing a calibration procedure after the magnetic field sensor is physically constrained to the outer insulator of the electrical power cable, and during which calibration procedures an electrical current of a known RMS current level is supplied to the electrical power cable, a second plurality of magnetic field strength measurements are obtained from the magnetic field sensor while the electrical current of the known RMS current level is flowing through the electrical power cable, and the processor calculates an RMS value of the second plurality of magnetic field strength measurement and divides the RMS value of the second plurality of magnetic field strength measurements by the known RMS current level to derive the constant.

8. The apparatus of claim 7, wherein the electrical power cable has a circular cross-section.

9. The apparatus of claim 7, wherein the processor is configured to:

derive, with the computing apparatus, a measure of power consumption of the power consuming device based on the measure of electrical current flowing through the electrical power cable during operation of the power consuming device.

10. The apparatus of claim 7, wherein the single magnetic field sensor is a single inductive coil.

11. The apparatus of claim 7, wherein the analog-to-digital converter and the processor are contained within an RFID tag, wherein the RFID tag is connected by a cable to a package that includes the single magnetic sensor.