Coating Thickness Gauge QualiCTG I: Dual-Principle Non-Destructive Measurement
Accurate coating thickness measurement protects product quality, prevents premature corrosion, and keeps production lines within specification. The QualiCTG I coating thickness gauge delivers non-destructive coating measurement on both ferrous and non-ferrous metal substrates through a single integrated probe. It combines magnetic induction and eddy current principles in one handheld instrument, so inspectors do not need to switch probes when moving between steel and aluminum parts.
Designed for paint inspection, galvanizing verification, and plating thickness checks, the QualiCTG I serves quality control teams across automotive, metal finishing, and hardware manufacturing operations. This page explains how the gauge works, where it applies, and how to specify it for your inspection workflow.
How a Coating Thickness Gauge Works
A coating thickness gauge measures the distance between a probe tip and a metal substrate without damaging the coating. The QualiCTG I uses two electromagnetic principles to cover both ferromagnetic and non-ferromagnetic substrates: magnetic induction for ferrous metals and the eddy current method for non-ferrous metals. The gauge selects the correct principle automatically when the probe contacts the surface.
Magnetic Induction on Ferrous Substrates
The magnetic induction method measures non-magnetic coatings on ferromagnetic substrates such as steel, iron, and nickel. The probe contains a permanent magnet and a coil. When the probe touches the coated surface, it generates a magnetic field that passes through the non-magnetic coating (paint, lacquer, zinc, chrome, or plastic) and into the ferrous substrate beneath.
The strength of that magnetic field depends on the distance between the probe tip and the substrate surface. A thicker coating increases that distance, which weakens the magnetic flux the coil detects. The gauge's electronics convert this flux change into a thickness reading. Because ferromagnetic materials attract magnetic fields strongly, this method delivers fast, reliable results on steel and iron parts.
Eddy Current Method on Non-Ferrous Substrates
The eddy current method measures non-conductive coatings on electrically conductive, non-ferromagnetic substrates such as aluminum, copper, and brass. This principle relies on Faraday's law of electromagnetic induction. The probe drives a high-frequency alternating current through a coil, which produces an oscillating magnetic field at the probe tip.
When this field reaches the conductive substrate, it induces circulating currents (eddy currents) in the metal surface. These eddy currents generate their own opposing magnetic field. The probe measures the resulting impedance change, which varies with the distance between the coil and the substrate. A thicker coating means a greater distance and a weaker eddy current response. The gauge converts that impedance shift into a precise thickness value.
Automatic Substrate Detection
The QualiCTG I integrates both sensor types into a single probe. During the measurement stroke (the moment the spring-loaded probe retracts into the instrument body upon contact), the gauge tests the substrate's magnetic response. It identifies whether the base metal is ferromagnetic or non-ferromagnetic and applies the correct measurement algorithm. This automatic detection eliminates manual mode switching, reduces operator error, and speeds up mixed-substrate inspection tasks.
How to Select and Specify a Coating Thickness Gauge
Choosing the right coating thickness gauge starts with understanding your substrates and coatings. Consider these factors:
- Substrate type. Confirm whether your parts are ferrous (steel, iron), non-ferrous (aluminum, copper, brass), or a mix. The QualiCTG I handles both with its dual-principle probe.
- Coating range. Match the gauge's measurement range to the thickest coating you expect to encounter. The QualiCTG I covers 0 to 2,000 micrometers, which suits most paint, plating, and powder coating applications.
- Accuracy requirements. For critical corrosion protection inspections, verify that the gauge's accuracy (plus or minus 2.5% + 1 micrometer for the QualiCTG I) meets the applicable standard or customer specification.
- Surface geometry. The minimum radius of curvature the QualiCTG I can measure is 5 mm on convex surfaces and 25 mm on concave surfaces. If your parts have tighter curves, plan probe placement accordingly or consider a gauge with a smaller probe diameter.
- Minimum substrate thickness. The substrate must be thick enough for the measurement principle to function correctly: at least 0.30 mm for ferrous metals and 0.05 mm for non-ferrous metals on this model.
- Data handling. Decide whether on-board storage (320 readings), statistical display (min, max, mean, standard deviation), and USB export meet your reporting needs, or whether you need Bluetooth or larger memory.
- Calibration method. The QualiCTG I supports zero calibration (on the bare substrate) and point calibration (using a known-thickness calibration shim). Confirm that your quality system accepts these methods.
Frequently Asked Questions
What Is a Coating Thickness Gauge Used For?
A coating thickness gauge measures the thickness of surface coatings (paint, plating, lacquer, powder coating, or plastic film) on metal substrates without destroying the coating. Quality control teams use it to verify that applied coatings meet minimum and maximum thickness specifications, which directly affect corrosion protection, adhesion, and appearance. It is a standard non-destructive testing tool in automotive, metal finishing, and manufacturing industries.
How Does the QualiCTG I Detect the Substrate Type Automatically?
The QualiCTG I probe contains both a magnetic induction sensor and an eddy current sensor. When the probe contacts the coated surface, the instrument tests the substrate's magnetic response during the measurement stroke. If the substrate is ferromagnetic, the gauge applies the magnetic induction algorithm. If the substrate is non-ferromagnetic but conductive, it applies the eddy current algorithm. This automatic detection takes less than 0.5 seconds.
What Coatings Can the QualiCTG I Measure?
The gauge measures any non-conductive coating on a metal substrate: paint, lacquer, enamel, powder coating, plastic film, rubber, and similar materials. On ferrous substrates, it also measures non-magnetic metallic layers such as zinc, chrome, copper, and aluminum plating. The key requirement is a sufficient difference in magnetic or conductive properties between the coating and the substrate.
How Do I Calibrate the QualiCTG I?
The QualiCTG I supports two calibration modes. Zero calibration requires placing the probe on the uncoated (bare) substrate to set the zero reference. Point calibration uses a certified calibration shim of known thickness placed on the bare substrate. Together, these methods correct for substrate-specific variations in magnetic permeability or electrical conductivity, ensuring accurate readings on your actual parts.
Does Surface Roughness Affect Measurement Accuracy?
Yes. Rough or textured surfaces increase the effective distance between the probe and the substrate, which can produce higher readings. For rough coatings, take multiple measurements across the area and use the statistical average function. Calibrating on a representative uncoated surface with similar roughness further reduces this error.
Can I Use the QualiCTG I on Curved Parts?
The gauge measures accurately on convex surfaces with a radius of curvature of 5 mm or larger and on concave surfaces with a radius of 25 mm or larger. The minimum measurement area requires a flat or gently curved zone at least 15 mm in diameter around the probe contact point. For very small or tightly curved parts, position the probe at the flattest region and avoid edges.
