All You Need to Know About Thickness Gauges

What is a thickness gauge?

A thickness gauge is a hand-held measuring device used to measure the thickness of a given materials or sample. They are frequently used in product manufacturing and engineering operations that require a specific object thickness in order to comply with governmental regulations.

How does a thickness gauge work?

This will depend on the type of thickness gauge, however, ultrasonic thickness gauges work by measuring the amount of time taken for sound to travel from the gauge through the material to the rear end of the object and back to the gauge. Through this, the gauge can then process data based on the amount of time taken for sound to pass through the designated sample.

Types of thickness gauge

Ultrasonic thickness gauge

Ultrasonic thickness gauges employ sound waves to measure the thickness of a sample by measuring the amount of time taken for sound to travel through the sample and back to the meter.

Coating thickness gauges

Coating thickness gauges are highly-versatile thickness gauge models designed specifically for measuring the thickness of non-magnetic and insulation coatings on ferrous materials such as steel, and non-ferrous materials including plastic and brass, that is applied to industrial-grade tools.

These gauges can measure the thickness of moulded plastic on industrial saws, drills and grinding tool handles as well as medical products used in surgery and dentistry to ensure adequate comfort and safety. Certain varieties of thickness meters such as paint coating thickness gauges can also be used to measure the thickness of paint in car auto-repair and bodywork garages.

What can be measured with a thickness gauge?

Digital thickness gauges and meters are highly-versatile devices that can be used in a wide span of applications:

Vehicle / automotive industry – Most types of thickness gauges are used in the automotive industry and can be used to measure the thickness of metal sheets and highlight imperfections in car bodywork, as well as for measuring the thickness of glass panes used in vehicle windscreens. Ultrasonic thickness testing gauges are often required for highlighting manufacturing flaws, whilst specialist paint coating thickness gauges are used in car auto-repair and bodywork garages for applying the appropriate thickness of metallic paints.

Engineering & manufacturing – Following on from the automotive industry, large factories and engineering plants that produce anything from toys to vehicle and machine parts often require a thickness gauge to ensure the quality and consistency of parts on the production line. In engineering, aircraft parts in particular, need to be rigorously checked for flaws and imperfections; thickness gauges are used to accurately measure thickness of materials to ensure safety.

Jewellers – Specialist gold testing meters can be used to measure the thickness of gold and other precious metals. By using ultrasonic thickness measurement equipment, jewellers can detect whether a gold item contains a core of different material.

Building & construction – Thickness gauges are often used for testing the thickness of walls and building materials. By conducting thickness testing, builders and surveyors can ensure that solid walls do not contain any imperfections that are likely to make the building unstable. Similarly copper piping and industrial pipelines can also be tested on a regular basis in order to detect corrosion.

Highway & local authorities - Thickness gauges can also be used to test the thickness of supporting metal and concrete columns for bridges to ensure they comply with regulation and do not deteriorate prematurely.  These devices are most commonly used to detect air pockets in concrete and corrosion on steel frames and supports.

Tanks of fuel/ chemicals – Ultrasonic testing gauges can indicate whether excessive corrosion is taking place in storage tanks of fuel, chemicals.

Archaeology – Students and scientists can use non-destructive ultrasonic testing methods in order to analyse the thickness of excavated pots and sensitive materials.

Glass manufacturing – Ultrasonic thickness gauges are used to measure thickness of glass in furniture mirrors, housing window panes and in vehicle windscreens and reflective surfaces.

Medical – Coating thickness gauges are used to ensure that moulded plastic coatings on medical tools and utensils offer sufficient protection and are safe for use.

Industrial tools – One of the most common applications for coating thickness gauges, industrial-grade tools such as saws and power tools require adequate coatings to ensure the tool are both hard-wearing and safe to handle.

Thickness gauge calibration

The calibration process for thickness gauges will differ depending on the type of thickness gauge you are using. Coating thickness gauges can be calibrated in several ways including one-point calibration, foil calibration and two-foil calibration. Ultrasonic thickness gauges require approved calibration blocks.

One-point calibration

One point calibration is a standard calibration process that does not require foils, the procedure is conducted on a non-coated test piece by applying the gauge probe as close as possible to a designated measuring point. This calibration procedure only has one reference point which is the zero value hence the label ‘one-point’.

Foil calibration (Two-point calibration)

 This calibration procedure uses a calibration foil with a known thickness. To begin, a one-point calibration procedure is conducted, then a foil is placed on a non-coated test piece. The probe is then placed in the same designated measuring area, pointers on the device are then used to change the displayed thickness value until this corresponds to the thickness value of the foil.

This procedure is often chosen over one-point calibration when the users requires higher accuracy. In order to achieve this, a foil needs to have a thickness slightly greater than the layer thickness of the test object.

Two-foil calibration

Often used for more difficult thickness testing procedures, the two-foil calibration procedure requires two foils of different thicknesses (these are usually graduated, with foil one around 0.5x the test object thickness and the second around 1.0x object thickness). This calibration method utilises two reference points for the probe that relate to the thicker and thinner values.

This process is most commonly used for rough or un-even materials.

Ultrasonic calibration

The standard procedure for calibrating an ultrasonic thickness gauge is to use approved calibration blocks (also known as ultrasonic calibration standards) to check the linearity of the gauge; the blocks range in size from 1.5mm to 50mm. A typical procedure would include 4-5 separate tests with different mm blocks to ensure consistency. A probe is placed in a designated area on the calibration block, from which sound waves are emitted and received once the sound has penetrated to the rear side of the block; this test is then repeated starting with thinner blocks and moving up to the thicker blocks after each consecutive test.

Note: Some ultrasonic thickness gauges require the use of a coupling gel in order to eliminate gaps between the testing surface and the transducer.

Things to consider when buying a thickness gauge

Sample material – The sample material can influence the type of thickness gauge you need. A thickness gauge is ideal for most metals, plastics and ceramics, however rubber and composite products may require more advanced gauges with higher levels of penetration.

Thickness – When buying a thickness gauge you will need to ensure the thickness measuring range is adequate for the sample you wish to measure. Thicker materials tend to be measured at lower frequencies whilst, thinner samples require higher frequencies.

Geometry/ surface – The surface of the sample can affect the gauges ability to couple and obtain an accurate thickness measurement. Measurements on convex samples may need non-contacting immersion gauges for adequate sound coupling.

Resolution/ Precision – More expensive, professional thickness meters typically offer higher levels of precision compared with standard models. Higher precision may be required when dealing with fine samples such as lenses, glass and paints.

Cost – There are many types of thickness gauge for sale on the market today, ranging from highly sophisticated ultrasonic approved models to low-cost thickness gauge models. When buying a thickness gauge, it is crucial to consider the features you need on a regular basis; for example, if you are working to legislation you will require a certified thickness gauge which will be typically more expensive than a standard thickness gauge.