Certain ACPD versions take the current input and voltage measurement functions and combine them into a single probe.

In TSC equipment these are generally kept apart. This allows the current input points to be widely separated to produce a more uniform electric field giving more accurate sizing. In addition this approach allows many voltage probes to be associated with a single input current for monitoring purposes.

General advantages of ACPD include:

• Works on any metal type, including welds.
• Probes are inexpensive. This makes the technique ideal for monitoring, on-site or in a laboratory environment, using spot-welded pins.
• Very small increments in crack depth can be detected by comparing readings taken periodically with the same fixed probe.
• Provides a detailed crack profile, including information on on crack bridging.
• In a metal with large skin-depth, compared to the voltage probe size, inclination of the crack to the metal surface can be estimated.
• The a.c. skin effect concentrates currents at the surface so the currents required are much smaller than for d.c. potential drop.
• Defect depth can be measured with no upper limit.