Ground fault detection based on capacitive sensing

Patent metadata

Field	Value
Publication number	US-2016054370-A1
Application number	US-201514835696-A
Country	US
Kind code	A1
Filing date	Aug 25, 2015
Priority date	Aug 25, 2014
Publication date	Feb 25, 2016
Grant date	—

Abstract

A ground fault detection system based on capacitive sensing suitable for use in detecting a ground fault condition in electronic equipment (such as a PCBA) with a circuit ground electrically isolated from an isolation ground (such as chassis ground). The capacitive sensing system includes a capacitive sensor capacitively coupled to the system isolation ground, and a capacitance/data converter that captures sensor capacitance measurements for conversion to sensor data representative of a ground short. In one embodiment, the capacitive sensor includes a sensor electrode capacitively coupled to the system isolation ground by one of projected capacitance and a floating capacitor (such as 33 pf), and the CDC unit further includes sensor excitation circuitry configured to drive the sensor electrode, such that a sensor capacitance (projected or floating capacitance) is representative of an electrical condition of the system isolation ground. For sensing by projected capacitance, the capacitive sensor can include a driven shield.

First claim

1 . A ground fault detection system based on capacitive sensing, suitable for use in detecting a ground fault condition in electronic equipment including a circuit ground electrically isolated from an isolation ground, where the ground fault condition occurs when the circuit ground shorts to the system isolation ground, comprising:
a capacitive sensor capacitively coupled to the system isolation ground, such that a sensor capacitance of the sensor capacitor is representative of an electrical condition of the system isolation ground; and a capacitance-to-data conversion (CDC) unit coupled to the capacitive sensor, and referenced to the circuit ground, and configured to capture sensor capacitance measurements for conversion into corresponding sensor data, including:
capacitance acquisition circuitry configured to acquire measurements of sensor capacitance for the sensor electrode; and
data conversion circuitry configured to convert the sensor capacitance into sensor data representative of the electrical condition of the system isolation ground, including an isolated condition in which the circuit ground is isolated from the system isolation ground, and a ground fault condition in which the circuit ground shorts to the system isolation ground.

2 . The system of claim 1 , wherein
the capacitive sensor includes a sensor electrode capacitively coupled to the system isolation ground by one of projected capacitance and a floating capacitor; and the CDC unit further includes sensor excitation circuitry configured to drive the sensor electrode, such that a sensor capacitance of the driven sensor electrode is representative of an electrical condition of the system isolation ground.

3 . The system of claim 2 , wherein
the capacitive sensor further includes a sensor shield disposed over and insulated from the sensor electrode; the CDC unit further includes shield drive circuitry configured to drive the sensor shield to generate a shield E-field such that the sensor E-field is concentrated in the direction of the system isolation ground.

4 . The system of claim 2 , wherein the CDC unit is configured to convert sensor capacitance into sensor data based on capacitive charge transfer, and
wherein the sensor excitation circuitry is configured to provide sensor excitation at an excitation frequency with excitation/charging and transfer/discharging phases; and wherein the capacitance acquisition circuitry is configured to acquire measurements of sensor capacitance based on capacitive charge transfer by integrating charge stored into the sensor electrode during the excitation/charging phase, and then discharged from the sensor electrode during the transfer/discharging phase.

5 . The system of claim 1 further comprising a data processing unit configured to process the sensor data to detect a ground fault condition as an abrupt change in sensor data corresponding to the measured sensor capacitance.

6 . The system of claim 1 ,
wherein the electrical equipment includes at least one PCBA configured with electronic circuitry, and installed in a chassis; and
wherein the circuit ground is a PCB/local ground, and the system isolation ground is a chassis/system isolation ground.

Assignees

• Texas Instruments Inc

Inventors

• Fomin Evgeny
• Wang Andrew

Classifications

• G01R31/312 Primary

  by capacitive methods · CPC title

• G01R1/18

  Screening arrangements against electric or magnetic fields, e.g. against earth's field · CPC title

• G01R31/025 Primary

  Physics · mapped topic

• G01N27/22

  by investigating capacitance · CPC title

• G01R31/52

  Testing for short-circuits, leakage current or ground faults · CPC title