Thickness is the coating contract, and the test method decides whether the number means anything. XRF and eddy current each have windows and limits.
This intermediate guide covers coating thickness testing with XRF and eddy current.
Common Mistakes and How to Avoid Them
The pitfalls that show up most often in real projects, with the cause and the practical fix.
| Mistake | Why It Happens | Practical Fix |
|---|---|---|
| 1. Wrong method for the coating | False number | Match method to coating |
| 2. Uncalibrated instrument | False readings | Calibrate per standards |
| 3. Testing one spot | Variation hidden | Test per plan |
| 4. Position off-spec | Edge effect | Follow the spec |
| 5. XRF on wrong alloy | Wrong thickness | Set the alloy |
| 6. Eddy current on metal film | No reading | Use XRF |
| 7. No record | Trend invisible | Record per batch |
| 8. Standards not followed | Disputes | Follow the standard |
Best Practices That Hold Up in Production
The operating disciplines that separate a reliable line from a reactive one.
- Match the method to the coating
- Calibrate per the standard
- Test per a written plan
- Follow the spec position
- Record every reading
Implementation Roadmap
A practical sequence that can be adapted to your own project.
Process Flowchart
Thickness test flow
A step-by-step sequence with notes and cautions so every shift follows the same order.
- XRF reads metal films; eddy current reads non-conductive films.
- Position effects distort readings.
- Never test at an edge unless the spec says so.
- Calibrate on the same alloy.
Working Data & Formula Notes
Test data
Reference values for coating thickness testing.
| Component / Parameter | Working Value / Role | What Changes Mean (annotation) |
|---|---|---|
| XRF | Metal films | Alloy matters |
| Eddy current | Non-conductive films | Metal films fail |
| Calibration | Per standards | False readings mislead |
| Position | Per spec | Edges distort |
Reference Data
Specifications and references cited in this guide. Confirm final parameters with your line supplier.
Method selection
| Coating | Method | Note |
| Nickel or chrome | XRF | Alloy corrected |
| Paint or powder | Eddy current | Non-conductive |
| Anodize | Eddy current | Per type |
| Multi-layer | XRF | Per layer |
Implementation Cases
Case 1 - XRF on the wrong alloy
Situation. Nickel readings were 20% high; the XRF alloy setting did not match the substrate.
Approach. The alloy was set correctly, calibration was checked, and the batch was re-tested.
Outcome. Readings matched the lab; the alloy setting is now verified before testing.
Case 2 - eddy current on a metal film
Situation. An operator used eddy current on nickel and got no useful reading; the method was wrong for the coating.
Approach. XRF replaced eddy current for the metal film and the method card was updated.
Outcome. Thickness passed; the method card prevents the mistake.
Frequently Asked Questions
Which method for what?
XRF for metal films, eddy current for non-conductive films.
Why calibrate?
Uncalibrated instruments produce false readings and wrong gates.
Why test per plan?
One spot hides variation; a plan shows the batch.
Why position matters?
Edges and curves distort the reading; follow the spec.
Why the alloy setting?
XRF thickness depends on the alloy; a wrong setting gives a wrong number.
Why record every reading?
The record builds the trend and settles disputes.
What standards?
ISO or ASTM thickness methods per your customer spec.
What if readings vary?
Check position, calibration and sample plan before blaming the line.
Who owns the method card?
QC, with the standard referenced on the card.
What Would You Like to Solve?
Tell us your coating types, substrate and current method. We can help set the method card, calibration and test plan for your lab.
Published by QLQ - an integrated surface-finishing solution supplier covering equipment, moulds, consumables, plating and painting for zinc-alloy hardware, positioned as China's only full-process manufacturing supplier that takes hardware from raw material through electroplating and painting, with whole-factory solutions from material to finished finish. Values cited are project references; confirm with your line supplier before specification.