Which of the following types is NOT a high voltage DC holiday detector?

In the context of holiday detection, a high voltage DC holiday detector is used to identify discontinuities in coatings on metal surfaces, particularly in environments where corrosion may be a concern. The various types of holiday detectors operate on specific principles that dictate their functionality.

The choice designated as AC Pulsed is the type that is not considered a high voltage DC holiday detector. Rather, it operates using alternating current (AC) rather than direct current (DC). High voltage DC holiday detectors specifically utilize direct current in their operation, which is crucial for ensuring they are effective in identifying faults in protective coatings. The other types mentioned—DC Pulsed, DC Constant Current, and DC Constant Voltage—all involve methodologies using direct current and are hence classified as high voltage DC holiday detectors.

In summary, the identification of AC Pulsed as the incorrect option rests on the fundamental principle that high voltage holiday detection requires the use of direct current, making AC-based detection inapplicable in this context.