Why Coating Thickness Readings Change Between Different Probes Malaysia

Different coating thickness probes can produce slightly different readings—even when they are used on the same painted metal surface.

This does not automatically mean that one instrument is faulty.

For coating inspection work in Malaysia, the result may be affected by the probe design, substrate material, surface shape, calibration method and operator technique. Understanding these factors helps users obtain more repeatable measurements from instruments such as the Landtek CM-8826F/N coating thickness meter.

What Does a Coating Thickness Probe Measure?

A coating thickness meter normally determines the distance between the probe and the underlying metal substrate.

The measurement method depends on the substrate:

Ferrous measurement is commonly used for non-magnetic coatings over steel or iron.
Non-ferrous measurement is commonly used for non-conductive coatings over aluminium and other suitable non-ferrous metals.

The CM-8826F/N is a dual-function model designed for both ferrous and non-ferrous applications. Its external probe is useful when the measurement location is difficult to reach or when the display needs to remain visible during inspection.

However, the probe still needs to be selected, calibrated and positioned correctly.

Why Do Different Probes Produce Different Readings?

1. Different Probe Designs

Not every probe has the same internal coil, magnetic circuit, contact surface or measurement response.

Differences in probe construction may affect how the instrument responds to:

Thin coatings
Thick coatings
Small components
Curved surfaces
Rough surfaces
Edges and corners
Different metal substrates

This means two different coating thickness meters may not show exactly the same value at one location.

A small difference does not necessarily indicate a defect. The user should consider the instrument accuracy, calibration condition and actual surface variation.

2. Ferrous and Non-Ferrous Measurement Are Different

A probe configured for steel should not be treated as identical to one used for aluminium.

For example:

Paint on mild steel normally requires ferrous measurement.
Paint on aluminium panels normally requires non-ferrous measurement.
Galvanised steel may require more careful interpretation because the substrate and coating system can be more complex.
Plastic, wood, glass and concrete are generally not suitable substrates for a conventional Fe/NFe coating thickness meter.

Before measuring, confirm the underlying material instead of judging only by the visible coating.

3. Calibration Was Performed on a Different Substrate

A coating thickness meter may be checked on the supplied zero plate and then used on an actual industrial component.

The result can change because the actual part may have a different:

Metal composition
Electrical conductivity
Magnetic property
Surface roughness
Thickness
Shape
Curvature

For better repeatability, perform the zero check and calibration on an uncoated sample that is similar to the actual workpiece, where possible.

If an identical uncoated sample is unavailable, record the limitation and verify the instrument using suitable reference foils or standards.

4. The Surface Is Curved

Probe response may change when measuring:

Small pipes
Cylindrical tanks
Curved vehicle panels
Steel rods
Rounded corners
Small fabricated components

A probe calibrated on a flat plate may produce a different result on a strongly curved surface.

The smaller the component or tighter the curvature, the more carefully the reading should be evaluated.

For pipe or curved-surface inspection, use a consistent probe position and repeat the measurement several times.

5. Measurements Are Taken Too Close to an Edge

Readings near an edge, hole, weld or corner may be less stable because the probe’s measurement field is affected by the surrounding geometry.

Avoid measuring directly beside:

Sheet-metal edges
Bolt holes
Weld beads
Sharp corners
Cut-outs
Raised markings
Deep surface defects

Where an edge measurement is unavoidable, take several readings from consistent positions and note the measurement location in the inspection report.

6. Probe Pressure and Angle Are Inconsistent

The probe should normally contact the surface firmly and vertically.

Unstable readings may occur when the operator:

Tilts the probe
Slides it across the surface
Applies uneven pressure
Measures while the probe is moving
Allows the probe cable to pull sideways
Places the probe over dirt or loose particles

Place the probe down smoothly, wait for the reading and lift it vertically before taking the next measurement.

An external probe such as the one used with the CM-8826F/N gives the operator more flexibility, but the probe cable should not interfere with positioning.

7. The Coating Surface Is Rough or Uneven

Industrial coatings are not always perfectly uniform.

Real coating thickness may vary because of:

Spray pattern
Brush marks
Surface preparation
Corrosion pits
Sandblasting profile
Powder-coating distribution
Multiple coating layers
Local repair work

One reading should not be used to represent an entire component.

Take multiple measurements and use the average, minimum and maximum values according to the inspection requirement.

8. The Probe Tip Is Dirty or Damaged

Paint residue, metal dust, oil or dirt on the probe tip can prevent proper contact.

Before testing:

Inspect the probe tip
Remove loose contamination carefully
Check the probe cable
Confirm that the connector is secure
Look for visible wear or damage
Perform a zero check

Do not scrape the probe tip using sharp tools because this may damage the contact surface.

9. Temperature Can Affect Measurement Stability

A large temperature difference between the instrument, probe, reference plate and workpiece may influence measurement stability.

This may occur when moving the instrument between:

An air-conditioned office and a hot factory
Indoor storage and an outdoor site
A cool vehicle and a sun-heated metal surface
Dry storage and a humid production area

Allow the instrument and workpiece to stabilise where practical before performing precision comparison measurements.

10. The Actual Coating Is Not Uniform

Sometimes the instrument is blamed even though the coating itself genuinely varies.

This is common on:

Repainted vehicle panels
Protective steel structures
Fabricated machinery
Storage tanks
Marine components
Powder-coated enclosures
Repaired or touched-up areas

To determine whether the variation comes from the instrument or the coating, check the meter on a suitable zero plate and reference foil before repeating the surface measurement.

Five-Step Checking Method for More Repeatable Results

Use this simple procedure before deciding that the coating thickness meter is inaccurate.

Step 1 – Confirm the Substrate

Determine whether the base material is:

Steel or iron
Aluminium or another suitable non-ferrous metal
An unsupported non-metallic material

Select the correct Fe or NFe measurement function.

Step 2 – Perform a Zero Check

Check the instrument using a suitable uncoated substrate.

Whenever possible, use an uncoated sample with similar material, thickness and shape to the actual component.

Step 3 – Check with a Reference Foil

Place a known reference foil on the zero plate or representative uncoated substrate.

Compare the displayed reading with the reference value and adjust the instrument according to the operating procedure if required.

Step 4 – Take Multiple Readings

Take at least several readings within the selected inspection area.

Do not rely on only one measurement. Observe whether the readings are consistent or whether the coating itself changes across the surface.

Step 5 – Avoid Problematic Locations

Keep a reasonable distance from:

Edges
Holes
Welds
Sharp curves
Heavy surface contamination
Damaged coating

If these areas must be inspected, document the position and interpret the reading carefully.

External Probe vs Built-In Probe

A built-in probe coating thickness meter can be convenient for quick, one-handed inspection on open and relatively flat surfaces.

An external probe model such as the Landtek CM-8826F/N may be more suitable when:

The measurement point is difficult to reach
The user needs to see the display while positioning the probe
The inspection area is inside machinery or a fabricated structure
Probe positioning requires more flexibility
Repeated industrial measurements are required

However, an external probe does not automatically guarantee higher accuracy. Calibration, positioning, substrate condition and operator technique remain important.

When Should the Instrument Be Checked?

Further checking may be required when:

The meter cannot complete a zero check
Readings remain unstable on a clean reference plate
Reference-foil results are consistently outside the expected tolerance
The probe cable or connector is damaged
The probe has been dropped
Different readings continue after correct calibration
The instrument is required for quality documentation or audited inspection

A calibration certificate confirms instrument performance under specified calibration conditions. It does not remove errors caused by an unsuitable substrate, poor probe placement or incorrect field procedures.

Choosing a Coating Thickness Meter in Malaysia

Before selecting a model, confirm:

Ferrous, non-ferrous or dual-function measurement
Built-in or external probe
Expected coating thickness range
Minimum component size
Flat or curved surface
Required accuracy
Calibration and documentation needs
Indoor, outdoor or factory application

The CM-8826F/N is particularly relevant for users who need dual Fe/NFe measurement with the flexibility of an external probe.

It may be considered for automotive paint inspection, metal fabrication, machinery maintenance, protective coating checks and general industrial applications in Selangor, Kuala Lumpur, Johor, Penang and other parts of Malaysia.

Need Help Checking Your Coating Thickness Meter?

Send MTM Precision a clear photograph of the instrument, probe, model label, workpiece and the unstable or unexpected reading.

Also tell us:

Substrate material
Expected coating thickness
Surface shape
Calibration method used
Reference-foil value
Several repeated readings

This information helps determine whether the variation is caused by calibration, probe positioning, substrate condition, coating variation or a possible instrument problem.

MTM Precision Sdn Bhd
Showroom & Service Centre: No. 29-1 & 29-2, Jalan Bandar 18, Pusat Bandar Puchong, 47160 Puchong, Selangor, Malaysia
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my