Measuring the paint or measuring the wall.
On a painted, galvanised or anodised metal part there are two different questions that sound like one: how thick is the coating, and how thick is the metal underneath. Each one needs a different instrument.
You want the coating's thickness — paint, galvanising, anodising, chrome plating — on metal: that's a QC.
You want the base metal's thickness, even though it's painted, without stripping the part: that's a QS with echo-echo mode.
The coating, or through it.
QC: coating thickness
On a ferrous substrate (steel, iron), the probe generates a magnetic field that attenuates according to the coating's thickness; the instrument translates that attenuation into a thickness value. On a non-ferrous substrate (aluminium, brass, non-magnetic stainless steel), the probe induces high-frequency currents in the base metal and measures the change in impedance caused by the coating on top.
Models with automatic substrate detection identify which base they're on without manual selection. In both cases, the QC measures the coating itself — it says nothing about the condition of the metal underneath.
QS: wall thickness, through the paint
On uncoated metal, a single echo is enough — the one that bounces off the back wall (pulse-echo mode). On painted metal, the QS5 uses echo-echo mode: instead of a single echo, it measures the time between two internal echoes — the paint/metal interface and the back wall — and so discards the paint thickness from the calculation, with no need to strip the part to measure it.
That's the key difference from normal mode: if you measure a painted part in pulse-echo by mistake, the paint's thickness gets added to the metal's, and the result comes out higher than the true value.
By what you need to know.
| What you want to know… | Instrument | Why |
|---|---|---|
| The thickness of the paint, galvanising, anodising or chrome plating | QC | Measures the non-conductive coating directly on the base metal |
| The metal's thickness, without stripping the part | QS, echo-echo mode | Discards the paint thickness from the calculation and measures only the metal wall |
| Ferrous substrate (steel, iron) | QC, ferrous or automatic model | Magnetic induction principle |
| Non-ferrous substrate (aluminium, brass, non-magnetic stainless steel) | QC, non-ferrous or automatic model | Eddy current principle |
| Coating on a non-metallic substrate (plastic, wood) | Neither | The QC only measures coatings on metal; it's outside its scope |
| Mapping corrosion or pitting under the paint, not the paint's thickness | QS5 with B-Scan | Analyses the condition of the metal surface, not the paint layer |
What usually goes wrong, and why.
Confusing the two questions
"How thick is the paint?" and "is the metal underneath the paint sound?" are different questions, and each one needs a different instrument — the QC doesn't report on the metal's condition, and the QS in echo-echo mode doesn't report on the paint's thickness.
Using a QC probe for the wrong substrate
Using a ferrous-substrate probe on aluminium, or vice versa, gives meaningless readings or no reading at all. If you work with both substrates, the model with automatic detection avoids the mistake.
Measuring a painted part in pulse-echo mode
Without activating echo-echo mode, the paint's thickness gets added to the metal's in the reading, and the result comes out higher than what the wall actually measures.
Expecting the QC to measure on plastic or wood
The QC measures coatings on a metallic substrate. A coating on plastic or wood is outside its scope, even if the paint itself is identical.
One instrument for each question.
I need the coating's thickness
Paint, galvanising, anodising or chrome plating, on ferrous or non-ferrous substrates. QC5 (automatic substrate detection) and QC3 series.
See the QC instruments
I need the metal's thickness, without stripping it
Echo-echo mode on painted or coated parts. QS5 DLE series, with corrosion mapping included.
See the QS instruments
Coating or wall?
Tell us what you need to know, whether the substrate is ferrous or non-ferrous, and whether the part is painted. We'll confirm the instrument and the model that fits.
