Holiday testing circuit for coated surface inspection

A device for detecting defects in a coating applied to a surface of a metallic asset, the device comprising:

• a detection circuit, including
• a probe having a conductive tip configured to be moved along the coated surface of the metallic asset during inspection;
• a switched input signal generator for providing a switched input signal to the conductive probe;
• a measurement device for measuring a signal response of the detection circuit, wherein the signal response is a function of the switched input signal and one or more electrical properties of the metallic asset and the coated surface of the metallic asset contacted by the conductive tip, and wherein the signal response is one or more of:
• a transient voltage magnitude,
• a magnitude of current flow through the probe,
• a rate of change of the measured voltage over time, and
• an amount of current flowing through the probe over time;
• and
• a processor operatively connected to the measurement device, wherein the processor is configured to compare the measured signal response to a baseline signal response, wherein the baseline signal response is the signal response of the circuit measured in the absence of a holiday,
• wherein the detection circuit is configured to detect a holiday based on the measured signal response and without any common ground connection between the detection circuit and the metallic asset,
• wherein the detection circuit is configured to measure one or more of a peak voltage and an average voltage, and wherein during operation the processor is configured to monitor changes in the measured voltage and detect a holiday when the voltage achieved during a given cycle period drops below a threshold voltage.

A device for detecting defects in a coating applied to a surface of a metallic asset, the device comprising:

• a detection circuit, including
• a probe having a conductive tip configured to be moved along the coated surface of the metallic asset during inspection;
• a switched input signal generator for providing a switched input signal to the conductive probe, wherein the input signal is a square wave having a switching frequency in the range of 10 kHz-100 kHz and a peak voltage in the range of 5-10V;
• a measurement device for measuring a signal response of the detection circuit, wherein the signal response is a function of the switched input signal and one or more electrical properties of the metallic asset and the coated surface of the metallic asset contacted by the conductive tip, and wherein the signal response is one or more of:
• a transient voltage magnitude,
• a magnitude of current flow through the probe,
• a rate of change of the measured voltage over time, and
• an amount of current flowing through the probe over time;
• and
• a processor operatively connected to the measurement device, wherein the processor is configured to compare the measured signal response to a baseline signal response, wherein the baseline signal response is the signal response of the circuit measured in the absence of a holiday,
• wherein the detection circuit is configured to detect a holiday based on the measured signal response and without any common ground connection between the detection circuit and the metallic asset.

A device for detecting defects in a coating applied to a surface of a metallic asset, the device comprising:

• a detection circuit, including
• a probe having a conductive tip configured to be moved along the coated surface of the metallic asset during inspection,
• a power source,
• a switched input signal generator configured to generate a high-voltage switched input signal using the power source and output the high-voltage switched input signal to the conductive probe, wherein during operation the signal generator and probe are configured to create a voltage potential at the conductive tip suitable for arcing between the metallic asset and the conductive tip when the conductive tip is proximate to a defect in the coating,
• a sensing resistor,
• a measurement device for measuring a signal response of the detection circuit, wherein the signal response is a change in one or more electrical parameters of the switched input signal as a function of arcing between the metallic asset and the conductive tip, wherein the measurement device measures one or more of a voltage and a current across the sensing resistor, and wherein the sensing resistor is provided at one of:
• a low-voltage side of the detection circuit wherein the low-voltage side is between a power source and the switched input signal generator, and
• a high-voltage side of the detection circuit wherein the high-voltage side is between the switched input signal generator and the probe,
• wherein the detection circuit is configured to detect arcing based on the measured signal response, thereby detect the existence of a holiday, and wherein the detection circuit is configured to detect arcing without reference to any common ground connection between the detection circuit and the metallic asset.