A practical guide to matching inspection requirements with instrument capabilities, probe configurations, frequency range, data acquisition, and performance verification. Choose the technique first—then the equipment that can demonstrate it works.
Assess access, expected crack orientation, geometry, lift-off, and scan coverage. Portable flaw detectors with suitable surface or pencil probes may be appropriate.
Consider rotating bolt-hole probes, multilayer techniques, encoder support, probe diameter, and the ability to distinguish structural features from discontinuities.
Evaluate bobbin, rotating, array, or specialized probes; differential and absolute channels; frequency mixing; encoded acquisition; and historical data comparison.
Choose a calibrated conductivity instrument appropriate to the material, thickness, curvature, temperature, and conductivity range.
Confirm that the instrument and probe support the actual measurement: nonconductive coating thickness, conductive-layer thickness, displacement, or another parameter.
Assess encircling or surface probe geometry, part speed, triggering, sorting outputs, repeatability, and integration with production controls.
Electrical conductivity, magnetic permeability, wall thickness, component geometry, and expected flaw depth influence the eddy current response. Frequency is not simply a depth setting: sensitivity, phase discrimination, probe response, and interference also matter.
Confirm the instrument can operate over the full required frequency range, with appropriate frequency increments and stable performance. Multifrequency capability is especially valuable when different responses must be compared or mixed—for example, in tubing inspection or layered structures. It does not guarantee detection of deeper flaws.
Measures the response of an individual sensing arrangement relative to a reference or balance condition. Often useful for general wall loss, conductivity changes, and localized discontinuities, depending on design.
Responds to differences between sensing elements or positions. Often emphasizes localized changes while reducing some slowly varying background responses; behavior depends on probe geometry.
Uses separate excitation and pickup functions. Probe design and spacing determine sensitivity and suitability for particular material and flaw conditions.
Common in tube or product inspection where circumferential coverage and repeatable movement are important. Confirm fill factor, diameter, speed, and coverage.
Provide specialized coverage or spatial information, often with additional acquisition and analysis requirements. Evaluate resolution and scan indexing.
Displacement, conductivity, coating, and production-line probes may require dedicated electronics and calibration approaches rather than general-purpose flaw detectors.
Frequency range, probe drive, gain, phase rotation, impedance-plane display, and channel-specific controls.
Filtering, sampling rate, mixing, dynamic range, and signal stability. Excessive filtering can distort or suppress relevant indications.
Raw-data recording, encoder inputs, channel count, data format, review software, historical comparison, and reporting capability.
Connector type, impedance matching, multiplexing, scanner interface, power requirements, and vendor-supported probe modes.
Battery life, environmental rating, weight, ruggedness, speed, remote operation, and integration with automation.
Calibration services, spare parts, software licensing, training, repair turnaround, and long-term data accessibility.
Eddy current array systems use multiple sensing elements to inspect an area or circumference with improved coverage and spatially referenced data. ECA is not a single probe design: coil geometry, operating mode, multiplexing, excitation, acquisition, and software vary substantially between surface arrays and tubing arrays.
Evaluate array width, element dimensions, coil orientation, overlap, lift-off tolerance, surface conformity, and sensitivity to cracks in different directions. Encoded scanning can support C-scan displays and repeatable location mapping, but positional accuracy depends on the encoder and scanning technique.
Confirm compatibility with the tube diameter, alloy, wall thickness, support structures, and expected degradation. Evaluate circumferential and axial coverage, probe centering, pull speed, array geometry, channel modes, and the ability to review raw signals and historical data. Do not assume surface-array performance translates to tubing.
Ask how many sensing elements are acquired, how they are excited and sampled, and whether multiplexing introduces dead time, cross-talk, or speed limits. The number of coils is not necessarily the number of simultaneously acquired independent channels.
Compare effective sample rate per element, scan speed, encoder resolution, synchronization, missed-data handling, and file size. Verify that acquisition density is sufficient for the smallest relevant indication at the intended inspection speed.
Look for impedance-plane signals, strip charts, C-scan or other mapped displays, channel selection, signal review, calibration tools, annotation, export, and traceability. A C-scan is a spatial representation of measured response—not a direct photograph of flaw geometry or depth.
Demonstrate detection, characterization, and sizing using representative flaws, geometries, lift-off conditions, and scanning speeds. Check edge effects, element-to-element variation, probe wear, complex geometry, and orientation sensitivity. More elements do not automatically mean better probability of detection.
| Inspection | Typical system considerations | Demonstrate before purchase |
|---|---|---|
| Surface flaw detection | Portable instrument; suitable surface/pencil probe; adjustable phase, gain, and filtering | Required flaw sensitivity under representative lift-off and geometry |
| Bolt-hole inspection | Rotating probe/scanner; appropriate diameter; recording where required | Coverage, orientation response, and reliable indication detection |
| Heat exchanger tubing | Multiple frequencies/channels; bobbin and specialized probe support; mixing and recording | Tube-specific flaw response, supports/deposits, noise, and data review workflow |
| Conductivity testing | Calibrated conductivity meter; suitable frequency and probe | Accuracy on representative materials and operating conditions |
| Automated line testing | Sensor geometry; high-speed processing; sorting and control interfaces | Detection reliability at actual line speed and production variation |
| Surface ECA | Array geometry and orientation; multiplexing; encoding; C-scan and signal review software | Crack-orientation response, coverage, spatial resolution, repeatability, and performance at scan speed |
| Tubing ECA | Tube-compatible array probe; channel modes; circumferential coverage; encoded pull and raw-data review | Response to representative tubing degradation, support structures, pull speed, and channel-to-channel consistency |
Use the equipment directory to find manufacturers, then review the specialized technical resources relevant to your inspection.
Educational selection guidance only. Applicable procedures, codes, specifications, and demonstrated technique performance govern actual examinations. Verify internal resource links before publishing.