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Ultrasonic Thickness Gauge

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NDT-KITS supply high performance ut thickness gauge, our new product UE0073 with Live Color A-Scan and B-Scan, it’s very useful for customer to validate the testing results and check the bottom outline of testing part. The Adjustable GAIN, GATE and blanking function make it suitable to measure thickness on rough surface parts and super thick plate.

By using the Past Zero Detection Technology, our ut thickness gauge testing value is not affected by the echo intensity, material attenuation coefficient, gain and gate height, so the testing data has higher reliability. Our thickness gauge has real 0.01mm resolution; it can easily distinguish two test blocks that the thickness difference is only 0.01mm.

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Ultrasonic Thickness Gauge: The Ultimate Guide

Table of Contents


Have you ever asked yourself how an ultrasonic thickness gauge works as an inspection tool? 

Various materials, including metals, cast, alloys, plastics, and ceramics, are employed in the manufacturing industry to produce different components. But while the properties of these component materials are important for things like strength and durability, quality inspectors often rely on these properties to ascertain a product’s quality.

But here is the thing, the thickness specification often serves as the basis upon which other properties are derived and, as such, forms the basis of inspection for quality inspectors.

This guide outlines all you need to know about ut thickness gauge as an accurate inspection tool for measuring material thickness and how it works. 

So, if you’re ready, let’s dive in.

I. What is an Ultrasonic Thickness Gauge?

The ultrasound thickness gauge is a non-destructive method for assessing the thickness of a material, and it is widely used in various industries. Also, many materials can be measured with this technique by merely understanding the time it takes for the ultrasonic waves to return to the surface. Some materials that can be measured with ultrasonic thickness tester include metal, fiberglass, plastic, ceramic, composite, glass, or rubber. 

The travel of ultrasonic waves through metals has been observed to occur at a constant speed. Still, it can vary slightly with factors like temperature. However, the source of the wave is often from a piezoelectric sensor inbuilt into the measuring sensor head, which also records the reflected wave. 

II. Advantages of Ultrasonic Thickness Gage

Ultrasonic thickness gage has several benefits when compared to other inspection methods and these advantages include

  • Broad measurement range: Ultrasonic gauges are suitable for measuring as wide as 0.08 mm to 635 mm. It only depends on the material and transducer selection.
  • Highly accurate: The use of digital ultrasonic gauges gives highly reliable, accurate, and repeatable results.
  • Rapid response: Measurements often take one to two seconds for every point while displaying results as digital readouts.
  • Flexible: Using a proper setup, an ultrasonic gauge can be used by virtually all engineering materials, including metals, fiberglass, plastics, and composites.
  • Simple to use: Most ultrasonic gauging applications available employ uncomplicated pre-programmed gauge setups with only a small amount of operator contact.

III. How does Ultrasound Thickness Gauge Work?

You may already know that an ultrasonic thickness gage measures the thickness of components like pipes, tubes, and tanks, but how does it work?

This method is a high precision measuring technique using the time it takes for sound waves to travel through a sample piece after it has been projected by an ultrasonic transducer which acts as a probe to measure the thickness of sample material. 

However, since sound waves reflect from material boundaries, recording the echo time from the other side of the sample piece can help gauge the thickness, just like radars measure distance. The resolution can be as small as 0.001 mm. Also, multiple echo models can measure the metal thickness of coated components without removing the coating.

IV. Limitations of Ultrasonic Thickness Gauge

Admittedly, ultrasonic thickness tester has numerous benefits and a wide array of applications in different industries. At the same time, it also has its limitations, and some of them are listed below. 

  • It must undergo separate calibration for every material tested
  • Contact with the material must be adequate to get an accurate reading
  • Surface rust is a challenge for some devices to achieve a precise measurement 
  • Coupling material is required for some devices to couple the material and the probe
  • Reading the results requires some level of technical expertise

V. What can Ultrasonic Thickness Gauges be Used for? 

Especially in the manufacturing industry, ultrasonic thickness gauges have popular usage, especially for metals used for different products and components. Some regular instances of metals that are measured include.

Pipes and tanks – involve measuring corrosion in metal pipes and tanks and precision thickness measurement while manufacturing.

Automotive sheet metal – involves measuring complex shapes and geometry of automotive metals. 

Small-diameter tubing – involves measuring wall thickness and concentricity of the tubing.

Castings – involves thickness of hollow and complex geometry of ferrous and nonferrous castings. 

Turbine blades – involves the turbine blades of aircraft engine hollow wall thickness measurement. 

Machined parts: – involves wall thickness of machine parts during manufacturing against the design specification.

VI. What Materials can be Measured with an Ultrasound Thickness Gauge?

Most methods of measurements or inspection are sometimes limited in their use for specific materials. Fortunately, ultrasonic thickness testers have varied applications for numerous materials for different purposes, highlighted below. 

  1. Erosion – This process occurs when wearing a protective coating or substrate intended to protect a component caused by friction during repetitive mechanical movements. Nonetheless, an ultrasound thickness gauge does a great job of measuring the thickness of coated materials. 
  2. Corrosion – Metals often undergo a corrosion process when exposed to natural elements like moisture from the atmosphere. However, an ultrasonic thickness gauge is a precision non-destructive inspection tool that can measure the extent of corrosion in hidden internal parts of metals with access to a single face. 
  3. Metals – Ultrasonic thickness gauges are often used to measure various forged, machined, rolled, cast, or extruded metal components with a thickness range of between 0.2mm to 500mm, dependent on the grain formation. 
  4. Ceramics – almost all structural and electronic ceramics, for instance, ceramic tubing and valves, turbine blades, containers, and ceramic coatings, are better suited for ultrasonic gauging. Ultrasonic gauges are also employed for measuring elastic modulus using sound velocity measurement.
  5. Other Materials – With its ability to measure general metals and plastics, ultrasonic gauges are additionally used in a broad range of different applications, only a few of which are listed here, including rubber, glassware, soft contact lenses, wax patterns, and biological samples including soft tissues. 


If you want to know how to use ultrasonic thickness gauge? Click to know more. 

VII. Types of Ultrasonic Thickness Gages

Ultrasonic thickness gauges often come in different types based on application or transducers’ setup. However, the popular categories that are often considered include corrosion gauges and precision gauges. 

  • Corrosion Gauges

These ultrasonic thickness gauges are application-based. They measure corrosion in metals using the travel time interval of echoes between the front and back walls of the component. But that’s not all. They are also equipped to measure times between consecutive multiple echoes. 

  • Precision Gauges

On the other hand, precision ultrasonic thickness gauges are often used for various other materials apart from metals, including plastics, ceramics, glassware, and other materials used in the manufacturing industries. These gauges can measure a wide range of wall thicknesses of between 0.2mm to 500mm with good accuracy and precision hence the name. 


Check the top 10 ultrasonic thickness gauge manufacturers for your needs on various ut thickness gage.

VIII. Theory of Operation of UT Thickness Gauges

There are fundamental concepts and essential theories that you might need to understand to make sense of the operations of ut thickness measurement tool. These theories revolve around the types of wave patterns produced by different transducer setups and different probe methods to measure sample thickness accurately.

  • Single Echo 

To measure thickness using single-echo probes requires a dual element transducer with wave path compensation. The procedure generally involves measuring two thicknesses t1 and t2, for uncoated and coated components, respectively, then multiplying them with the velocity of sound for steel which is the material. 

The velocity of sound is often slower for materials with coatings like paints than that of uncoated metal. Hence, the single echo method will produce thickness greater than the combined thickness of coating and metal with a significantly greater, unknown value for paint thickness. Still, it is not merely a matter of subtracting the paint thickness measurement from the overall single echo measurement result. 

It means that adequate consideration should be given to an unknown coating constant when employing the single echo method in ultrasonic thickness gauges. 

  • Multiple Echo 

On the other hand, the multiple echo method of ultrasonic thickness probes often involves the consideration of time measurements of a minimum of three successive back wall echoes. Invariably, the multiple echo method only measures the time between echoes without considering if the materials (steel) are coated or not. Every time measured between echoes is considered the same. 

Moreover, for the multiple echo method, the thickness meter establishes thickness by adding the individual thicknesses t1, t2, and t3, dividing the result by six, and then multiplying the result with the velocity of sound for the steel material. What you get as the resultant thickness calculation from the instrument is, therefore, the exact measurement of just the steel thickness ignoring the coating thickness.

The velocity of sound is different for different materials. It is expressed in meters per second or inches per microsecond. For instance, sound travels through steel faster at 0.233 inches per microsecond than it travels through plastic 0.086 inches per microsecond.

IX. How do you Calibrate Ultrasonic Thickness Gages?

The process is commonly known as gauge calibration for ultrasonic thickness gages, often involves turning time measurement of echoes into thickness measurement using the velocity of sound in a standard sample material.

  • Velocity and Zero Calibration

For velocity calibration, the gauge takes the speed of sound in a standard sample of the test material then collects the value for determining the thickness from measured time intervals. However, material density and elasticity, grain structure, material composition, and temperature often affect sound velocity.

On the other hand, zero calibration measures a material sample of established thickness to determine a zero offset value that compensates for the portion of the total pulse travel time that indicates factors other than the main sound path for the test sample.

  • Calibration Certification

Calibration certification involves documenting the measurement precision of a thickness gauge for specific test conditions. Manufacturers’ calibration certification is often done with standard thickness reference with traceable thickness to international standard institutes.


➤ Related Article: How to Choose an Ultrasonic Thickness Gauge?

➤ Related Article: How to use Ultrasonic Thickness Gauge? 

➤ Related Article: Top 10 Ultrasonic Thickness Gauge Manufacturers

X. Factors that can Impact the Performance and Accuracy of Ultrasonic Thickness Gage

Different factors associated with test material, equipment, user skill, and component geometry can affect the level of accuracy for an application.


  1. Material-related factors


◼︎ Acoustic properties of the test material

Several acoustic properties that can affect the accuracy of and range of ultrasonic thickness measurements include: 

Sound scattering – In various materials such as cast iron, fiberglass, and composite materials, sound energy can scatter from individual grain edges or borders between different materials. 

Sound absorption – In many materials, including low-density plastics and rubber, sound energy is absorbed very rapidly.

Velocity variations – Without consistency in the sound velocity of material, there cannot be an accurate ultrasonic thickness measurement. 

Phase reversal or phase distortion – Ultrasonic gauges sometimes adopt the typical position where the test sample is supported by air or a liquid which has lower acoustic resistance than other materials.


◼︎ Physical properties of the test material 

Physical properties like shape, size, and surface finish of the test samples are critical considerations to determine the boundaries of measurement range and accuracy.

Surfaces roughness – Rough surfaces often lead to sound reverberations and consequently increase the minimum thickness measured. Therefore, a smooth surface on any side is necessary for accurate measurements. 

Taper or eccentricity – Returning echo is usually distorted for misaligned, tapered, or angled contact and back surfaces leading to inaccurate measurements. 

Curvature – Similar to misaligned test samples, curve-surfaced samples need properly aligned transducers to get accurate measurements.


  1. Operator-related factors


  • Beam alignment 

This consideration usually involves holding the transducer flat on flat surfaces and centering the transducers on the curve for curved surfaces. 

  • Coupling technique 

Where couplants are employed for measuring contact transducers, the couplant layer thickness becomes part of the measurement. A section of the zero offsets balances it. 


  1. Equipment-related factors


Though instrument design considerations like digital sampling rate often set the boundaries of range and accuracy for ultrasonic gauges, in applications, the range and accuracy are eventually determined by a combination of gauge, setup, transducer, and material-related factors.


In conclusion, the ultrasound thickness gauge is a useful inspection tool with various benefits that include high result accuracy, limited access requirement, and a wide range of measurements. 

Notwithstanding, you also need to choose the right ut thickness gauge for the right application as transducers’ setup, material grain structure, and acoustic nature of the material can be determining factors for an accurate result.

But whichever ultrasonic thickness gage you choose, you need to ensure suitability for your required application. It is from a supplier with a consistent track record of successful delivery. That’s all that matters. 

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