How to choose an eddy current tester
By Grant, Inspection Tool Specialists. Reviewed November 2026.
Three things decide which eddy current tester you need: whether the material conducts electricity, the defect or property you must find, and whether you inspect parts by hand or in-line on a moving product. Answer those first. The reference you calibrate against matters as much as the instrument.
This guide covers portable eddy current flaw detectors, conductivity meters and calibration blocks. Pipe and tube inspection is covered in the section on in-line systems.
How eddy current testing works
A coil carries alternating current, which induces eddy currents in the surface of a conductive material. A crack, a change in alloy, a change in thickness or a change in the distance between the coil and the surface all alter the coil's impedance, and the instrument displays that change. Eddy current works only on electrically conductive materials. Lift-off, the gap between probe and surface, changes the reading, so the probe must be held steadily and at the same distance as the reference.
Which instrument for which job?
| Job | Instrument | Typical in our range |
|---|---|---|
| Surface crack detection on conductive metal, including aviation work | Portable eddy current flaw detector | TMD-301, MET802, MET801, MET804 |
| Sorting alloys, checking heat treatment, conductivity checks | Eddy current conductivity meter | TMD-102 |
| Setting up and checking the instrument against known defects | Calibration block set | Eddy current calibration block set |
| In-line inspection of tube or wire | Dedicated station with a close-fit coil | Designed around the product; see below |
Calibrate against a reference, not a brochure
An eddy current result means nothing unless the instrument has been set up against a reference of the same material, similar geometry and a known defect. Calibration blocks give that reference. If the customer has no reference, the first step is to make one, with defects of known size, before any instrument is chosen or quoted.
In-line tube and wire inspection
For tube or wire moving through production, the tube's diameter, wall thickness, material and line speed decide the coil and the station layout. We ask for a demonstration first: the manufacturer shows detection of a tube with a known pinhole, alongside a sound reference tube. That sets the achievable sensitivity and avoids rejecting good tube. We would not recommend a model for an in-line station until that demonstration has been done.
Probe, frequency and surface
- Probe type: a surface probe suits flat or gently curved parts; a pencil probe suits small areas and bores; a coil around the product suits tube and wire. Choose the probe for the geometry, not the instrument.
- Frequency: lower frequencies penetrate deeper, and higher frequencies show surface defects more clearly. Frequency is set against the depth of the defect you must find.
- Magnetic materials: magnetic steel and iron affect the reading and need the probe and reference chosen for them.
- Coatings and roughness: a coating adds to the lift-off, and a rough surface gives noise. Clean the surface and use the same condition on the reference.
Procedure and standards
The procedure or specification your customer works to sets the reference standards and the acceptance criteria. Send it with the enquiry, because it determines the calibration, the records and the reporting.
Which instrument should I buy?
| Application | Suggested starting point |
|---|---|
| Portable crack detection, entry level | MET802 portable eddy current flaw detector |
| Portable flaw detection, aviation or demanding work | TMD-301 digital eddy current flaw detector |
| Higher-specification portable flaw detection | MET801 or MET804 |
| Alloy sorting and conductivity checks | TMD-102 conductivity meter |
| Calibration reference for any of the above | Eddy current calibration block set |
As a guide to our current range, including VAT: calibration blocks from about R6,200; the MET802 from about R31,500; the conductivity meter from about R82,900; the TMD-301 from about R187,300; the MET801 from about R203,000; the MET804 from about R442,000. Prices change, so check the product pages and confirm the probes and blocks each quote includes.
Questions we will ask you
Tell us the material and alloy, whether it is magnetic, the shape and size of the part or tube, the defect you need to find and its smallest size, the surface condition and any coating, whether inspection is by hand or in-line and at what speed, the procedure or specification you work to, and what records you must keep. With that we can recommend an instrument and provide pricing.