- Measuring range
- 0.0 to 500 µm with F500; 0.0 to 1500 µm with N1500; 0.0 to 2000 µm with N2000
- Accuracy
- ±(2% H + 0.3 µm) after five-point calibration, H being the standard value
- Repeatability
- ≤ (0.8% H + 0.1 µm) on F500 and N1500 with the hand press stand; ≤ ±(1% H + 0.2 µm) on N2000
- Probes
- F500 magnetic induction; N1500 and N2000 eddy current
- Minimum substrate thickness
- 0.1 mm on a ferromagnetic substrate; 0.03 mm on a non-ferrous substrate
- Minimum measuring area
- 7 mm
- Display
- 240 × 160 dot matrix LCD with Max, Min, Avg and Stdev of the last nine readings
- Calibration
- Zero point plus one to five calibration points
- Body
- 148 × 76 × 26 mm, four AAA alkaline cells
- Probe size
- F500 and N1500 110 mm long by 15 mm diameter; N2000 95.5 mm long by 30 mm diameter
A coating that is only a few micrometres thick is where a general-purpose gauge stops being useful. The reading is small, the tolerance is tighter than the reading, and the difference between one operator and the next becomes visible in the numbers. This instrument is aimed at that end of the work.
Product overview
One body, three probes, five ways of buying it. The body carries the display, the calibration and the statistics; the probe carries the coil and sets which method is applied and over what range.
The probes are deliberately small. Two of them are the size of a thick pen and read an area not much wider than a screw head, which is what makes a bolt, a bracket or a stamped contact readable at all. The third is wider and is aimed at painted board material and thicker coatings.
The body is held in one hand and the probe in the other, on a cable. A hand press stand can replace the hand for the two thin-coating probes, and that is the configuration the tighter repeatability figures belong to.
How the instrument measures a thin coating
Both methods measure a gap. Over a ferromagnetic substrate, the probe drives a magnetic circuit through the coating and measures how much the gap weakens it. Over a conductive non-ferrous substrate, the probe drives an alternating field and measures the eddy currents induced in the metal beneath, which change with the distance to the probe.
Neither method measures the coating directly. Both measure the effect of distance on a field, which is why the substrate has to be known before the number means anything, and why the instrument shows which substrate it believes it is on.
What makes a thin coating readable is the stability of that signal, not the size of the display. The probe digitises close to the coil, the instrument compensates for temperature, and the calibration corrects the offset on the bare part and the gain against foils of known thickness. The accuracy figure is quoted after a five-point calibration because that is the condition under which the linearity has been corrected; a one-point calibration leaves the far end of the range uncorrected.
The statistics on the screen are part of the measurement rather than a convenience. Taking several readings on one part and reading the spread tells the inspector whether the surface or the technique is the source of the variation.
How to select the right probe
The substrate decides the method, and the method decides the probe. Iron and ferromagnetic alloys take the magnetic probe; copper, aluminium, brass, magnesium and zinc take one of the eddy current probes.
The coating decides nothing about the method and everything about the range. A thin zinc or paint layer on steel sits inside the magnetic probe’s range with resolution to spare; a thick coating on aluminium needs the longer eddy current range.
The size of the part decides the probe more often than the range does. Where the measuring spot has to fit between a thread and a shoulder, the narrow probes are the only ones that will sit flat. Where the part is board material or a broad panel, the wider probe is easier to keep square.
The stand is a decision about the acceptance limit. If the tolerance is wide compared with the reading, hand pressure is good enough. If the tolerance is tight, the stand removes a variable the operator cannot feel.
Measurement limitations and selection considerations
A coating over a substrate thinner than the probe expects is not measurable, whatever the display says. Below the stated minimum substrate thickness the field passes through the part and into whatever is behind it, and the reading becomes a property of the bench rather than of the part. Thin sheet, foil and small machined parts are where this bites.
Edge and curvature effects are the second limit. Near an edge or on a tight radius the field has less material around it, and the reading drifts low rather than failing. The minimum area and radius are conditions of validity, not targets.
The method cannot separate layers. Primer, topcoat and clear coat on the same panel are read as one film, and a plated layer under paint is invisible to the reading. Where the individual layer thickness is the acceptance criterion, a cross-section is the only answer.
Finally, the probe is a precision part with a wear surface. A dropped or dragged probe drifts, and the drift appears as a slow change in the readings rather than as a fault. Checking against a known foil at the start of a shift is cheaper than discovering it at the end of one.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
