We’ve all been there.
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The desire and effort put into choosing the right device such as a coating thickness gauge can leave you disappointed and frustrated knowing you’ve given it all you have.
A coating thickness gauge is an essential tool for assessing the quality of a coated component or a piece of equipment like a vehicle. It gives you specific data like how long the vehicle has before corrosion sets in. This kind of information can help you assess the vehicle’s value and consequently allow you to bargain the price more accurately.
This guide contains all the information you need to choose the correct coating thickness gauge, including various applications and typical buying considerations.
Want to know more? Then let’s dive right in.
I. What are the Types of Coating Thickness Gauge?
Coating thickness gauges are sometimes referred to as paint meters. However, their function is to measure the thickness of coating material to ascertain the level of protection of the coated material, often known as the substrate. Interestingly, there are three general categories of coating thickness gauges, including digital, destructive, and mechanical coating thickness gauges, all of which have specific application areas.
Digital coating thickness gauges are often very versatile as inspectors use them to measure almost any material’s coating thickness, including ferrous and non-ferrous materials. They are also very accurate with a repeatable thickness measurement.
On the other hand, destructive coating thickness gauges are suitable for multi-coat paints and non-metallic substrates. However, they are not ideal for risky job areas like underwater or highly flammable environments where mechanical coating thickness gauges are most suitable.
II. What are the Applications for Measuring Coating Thickness?
Measuring the coating thickness on components is often found in different industrial and domestic operations, including
For Typical Coating Materials
These materials include paints, plastic, and enamel.
Insulating Coatings
Paints, enamel, plastics, and ceramics acts as insulating coatings on components that inspectors must check against design requirements.
Non-Ferrous Coatings
include chrome, brass, lead, zinc, and copper.
Ferro-Magnetic Coatings
Electroplated Nickel is a typical example of a ferromagnetic coating.
For Typical Substrate Materials
Includes both insulating substrates and non-ferrous substrates like Tin and aluminum.
Insulating Substrates
Plastics, epoxy, and glass are often used as insulating substrates and need coating thickness gauges to ascertain quality.
Non-Ferrous Substrates
Aluminum, bronze, and copper are typical examples of non-ferrous substrates that require coating thickness gauges.
Ferro-Magnetic Substrates
Using electroplated Nickel for ferromagnetic coatings often requires coating thickness gauges for quality assessment.
For Typical Coating Measurement Application
Different applications require coating thickness gauges, including insulation coatings with materials like paint, plastic, and enamel.
Automotive Refinishing Detection
Finished surfaces in the automotive industry are critical to ascertain the quality and value of the product. A poorly finished surface is seen as having low value.
General Industrial Measurement
Industrial measurement of coatings, especially on metallic substrates, are common, especially in anti-corrosion applications.
III. What to Look for When Buying a Coating Thickness Gauge?
Deciding on the most suitable coating thickness gauge for assessing the quality of coatings can sometimes be challenging. You’ll need a thorough understanding of the inspection requirements. Most importantly, careful consideration of some critical factors and features is essential for this process. Here are the vital elements you should never fail to consider when buying a coating thickness gauge.
- Measuring Range and Accuracy
– Usually, the maximum and minimum thickness measurable by a coating thickness gauge determines its range, and its accuracy is the level of acceptable tolerance for error built into it. These parameters are essential when looking for a suitable coating thickness gauge. The higher the accuracy and range, the better the device though this might also mean a higher price. Typically, the accuracy of a coating thickness gauge often comes as ±(3%+1um) but can change based on the material under inspection
.
- Battery and Power
– Coating thickness gauges get power from different battery types, including AAA and rechargeable batteries. But rechargeable battery-powered devices are preferred for obvious reasons like the convenience and charging options, including USB chargers. Still, other coating measurement devices do not need batteries at all.
- Display
– Different types of coating thickness gauges utilize different types of reading output. While some have a side scale to indicate reading values, others have a display screen for you to see the readings. Though devices with a display screen are better for the sake of easy usage, you need to ensure that the readings displayed on the screen are also easy to read without being crowded.
IV. How to Choose a Coating Thickness Gauge?
Many factors often determine the choice of a suitable coating thickness gauge. However, the type of coating material and the thickness measurement method often dictate these factors’ most critical. You’ll usually be the judge of the most critical factors to consider in choosing any coating thickness gauge for your inspection needs. Here are the essential elements for selecting an accurate coating thickness gauge.
- Measurement Occasion
– The measurement occasion often refers to the flatness and width of the surface. A high-precision coating thickness gauge might be most suitable when these parameters are substantial. On the other hand, smaller objects will only require a general coating thickness gauge with a more general precision that will suffice.
- Size of the Measured Material
– Size matters. And in selecting a suitable coating thickness gauge, the size of the material under examination is an essential consideration. Certain coating measuring devices are ideal for small bolts, screws, and nuts. But when it comes to bigger components, a more convenient coating thickness gauge will be required. You might even need fixtures to make the operation more suitable for massive objects.
- Measurement Range
– Choosing a coating thickness gauge with a suitable measurement range is essent
ial. However, the type of coating on the object will significantly affect the measurement range you will require for a coating thickness gauge. Mostly, a thickness range of 0 – 2000 μm is often acceptable, but for thicker coatings used in an anti-corrosive and fireproof application, a thickness range of up to 0 – 5000 μm might be required.
- Instrument Accuracy –
Depending on your purpose of using a coating thickness gauge, the level of accuracy you require might vary considerably and might also affect your choice of a coating thickness gauge. Generally, home or domestic use of coating thickness gauges doesn’t require the highest level of accuracy, and a cheap entry-level device might be enough. However, industrial usage often requires higher accuracy, and a more specialized coating thickness gauge will be suitable.
- Price
– Your budget is a critical determining factor when choosing a suitable coating thickness gauge. The price a supplier offers to give you a coating thickness gauge will be an essential determiner for making your choice, as your budget is a primary consideration when choosing a coating thickness gauge.
- Ease of Use –
Choosing a coating thickness gauge that is difficult to use can be a deal-breaker when choosing a coating thickness gauge. A more intuitive device with a readable display gives you less stress while measuring the coating thickness. It also makes you more effective and faster while carrying out your inspection. Additionally, a new user will quickly understand how it works without going through rigorous training to use it.
- Data Entry – S
ome coating thickness gauges do not offer any form of compatibility with a computer. As such, you only have the option of entering the data you’ve collected into a sheet of paper or a hardcopy book. However, some manufacturers give you proprietary software that allows you to connect your measuring device with your computer so that you can enter the data you’ve collected directly into your computer.
- Other Considerations
– You might have to consider other factors such as instrument automation, a minimum, and maximum measurable area, minimum measurable curve, and data collection ability of a coating thickness gauge. These considerations are also crucial in choosing a suitable coating thickness measuring device for your peculiar quality assessment needs.
V. How to Perform the Calibration with Coating Thickness Gauge?
Like most devices and equipment used in assessing the quality of a component, the coating thickness gauge has some level of error tolerance built-in. It will often need periodic checks to ensure that this tolerance has not been exceeded. Consequently, you’ll need to perform a calibration process to ensure you keep your coating thickness gauge within an acceptable error tolerance limit.
To perform the calibration of a coating thickness gauge is pretty easy and quick as most manufacturers provide accompanying software that can guide a user through the process.
The first step is to take about 5 to 10 measurements on an uncoated object to determine a zero point for the coating. Then set a calibration foil on the uncoated object and repeat the exact 5 – 10 measurements to get the nominal value as much as the film thickness corresponds to the object’s coating, the better the accuracy of the coating thickness gauge.
VI. What is the Detection Process of Coating Thickness Gauge?
Depending on whether the material under examination is ferrous or non-ferrous, the detection principle of a coating thickness gauge can differ significantly. However, the detection process of a coating thickness gauge is the same regardless of the material type.
The detection process often begins activating the device by pressing a power button or a switch. It might take a few minutes for the device to automatically calibrate itself to its surroundings to get accurate readings, for which you’ll have to wait. Next, set your desired configurations on the device with the appropriate buttons and carefully place them on the object for inspection. When you are set, simply start the operation.
➤ Related Article: How to Check Car Paint Thickness with a Coating Thickness Gauge?
Conclusion
In conclusion, choosing a suitable coating thickness gauge shouldn’t be difficult and frustrating if you know what factors to consider. Depending on the type of material, the risk associated with the work environment, and the level of accuracy you desire, your choice of a coating thickness will often be between a digital, mechanical, or destructive coating thickness gauge. However, the most important consideration you should use in making your choice includes resolution, speed, accuracy, measurement range, and ease of use. Don’t also forget to consider your budget, as this is, in most cases, the most critical factor.
4.9/5 - (59 votes)
The importance of measuring coating thickness is discussed extensively in the “How to Measure Coating Thickness” article. When it comes to selecting a handheld portable coating thickness gauge, an incorrect instrument choice may result in a measurement failure (e.g., inability to obtain a value) or completely wrong results.
Even when a false reading is obtained with an incorrect gauge for the job, there’s also a high risk of assuming it’s accurate.
For more information, please visit AJR.
The above factors increase the chances of failing to meet a desirable coating thickness specification. The consequences may lead to the added costs of rework or lost contracts due to customer dissatisfaction.
This article explores the factors that influence choosing the most suitable gauge for a specific application, first time, and ensure the measurements are fully representable of the actual coating thickness.
INFLUENCING FACTORS
When it comes to choosing a suitable coating thickness gauge, it’s essential to consider several crucial factors. Each one of them will determine what type of instrument and measurement probe are required.
The Physical State of a Coating
Initially, for coatings in a liquid state or the so-called ‘uncured state’, the traditional Dry Film Thickness (DFT) gauges won’t work. For such applications, non-contact powder coating thickness gauges are required. They function by placing the probe at a calibrated distance from a measured surface, and readings are obtained using the ultrasonic measurement principle.
This method is limited to powder coating applications, where a thickness needs to be predicted before the final curing stage. Once the depth is known, it’s possible to potentially reduce the powder consumption that leads to leaner coating application processes with financial and ecological advantages.
However, for coatings is their stable (cured) state, Dry Film Thickness (DFT) gauges are ideal instruments for these applications. They also test layers non-destructively and cover a significantly wide range of applications. In this instance, a measurement probe needs to be applied to a surface for a reading to take place.
This article guides a reader to choose the appropriate DFT gauge for measurements of coatings in their finished “cured” state.
Coating and Base Material
DFT Gauges work using either magnetic induction or eddy current measurement methods. The main difference between the techniques is that the first measures the coating thickness on Ferrous (Fe) while the latter on Non-Ferrous (NFe) substrates. Some gauges incorporate both principles in one to cover all possible base materials. The principle of operation can be seen in Figure 1 and Figure 2.
Figure 1. Schematic diagram of a probe incorporating magnetic induction method.
Figure 2. Schematic diagram of a probe incorporating eddy current amplitude sensitive method.
The magnetic induction measurement method works by generating a low-frequency magnetic field that is produced by excitation current I~. A measurement coil μmeasures the resulting magnetic field.
The Eddy current test method, (amplitude sensitive) measures according to ISO 2360 and ASTM 7091 standards. A coil wrapped around the ferrite core is induced with an excitation current. It generates a high-frequency magnetic field that sends loops of electrical current into a base material, in planes perpendicular to the magnetic field. The same coil measures the resulting magnetic field.
In both methods, the measurement coil sends a signal to the instrument (DFT gauge), which converts it into numerical units we can understand, such as microns or mils.
In case a coating has the same chemical composition as a substrate, there’s no way for a measurement probe to recognise the difference. Hence, it’s essential to understand what material a coating consists of and whether it’s measurable on a given substrate using a DFT gauge.
The table below demonstrates typical applications for both magnetic induction and eddy current methods. We also extensively talk about magnetic induction and eddy current measurement principles in the “How to Measure Coating Thickness” article.
MEASUREMENT PRINCIPLES AND THEIR MAIN APPLICATIONS
Magnetic Induction
Eddy Current
Substrate (Base Material)
Ferromagnetic (e.g., Steel or Iron) μm
Electrically conductive non-ferrous metal (e.g., Aluminium)
The Main Field of Application
– Non-ferromagnetic coatings
– Electroplated coatings made of chromium, zinc, copper or aluminium
– Paint, enamel, varnish or plastic coatings
– Electrically non-conductive coatings
– Paint, enamel, varnish or plastic coatings
– Anodic coatings
Helmut Fischer GmbH offers a wide range of DFT gauges with built-in or interchangeable probes that use magnetic induction and eddy current methods. Learn more about the instruments we suggest following the link below:
COATING THICKNESS (DFT) GAUGES
Wide range of handheld dry film thickness gauges (DFT) for the measurement of coating thickness on ferrous and non-ferrous substrates
Coating Roughness
If a coating is rough, then there will be a higher variation in the measured coating thickness. It happens since a probe tip may rest on peaks or in troughs. Probes that aren’t influenced by rough coatings solve this challenge Figure 3.
Figure 2. A schematic diagram demonstrating how peaks and troughs affect coating thickness readings [A] and the effect of wide and dual-tip probes that take consistent readings on rough surfaces [B].
Wide and dual-tip probes have a larger measurement area and always sit on peaks. This way, the total thickness of a coating is consistently measured. A list of probes offered by Helmut Fischer GmbH, specifically designed to measure on rough surfaces consistently, can be found in Table 1.
FD13H probe. Probes for measurements on virtually all metals. The probes work with two test methods and are therefore able to measure coating thicknesses on non-ferrous metals as well as on ferrous metals. Because of the large pole tip, the probes are also well suited for measurements on rough surfaces.
FTD3.3 probe. This probe utilises the eddy current method. It is suitable for measurements of rough paint, lacquer, plastics, and anodised coatings on Non-ferromagnetic substrates.
V7FKB4 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Higher repeatability precision than single tip probes when measuring rough surfaces.
FKB10 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Uniquely suited for thick layers (up to 8mm). Provide a much higher measurement precision on rough surfaces than single tip probes.
Table 1: Probes for measurements on rough surfaces
The above probes work with the FMP family of instruments. You can learn more by following the link below:
Wide range of handheld dry film thickness gauges (DFT) for the measurement of coating thickness on ferrous and non-ferrous substrates
The Location of the Measurement Area
The location of the measurement area also plays a significant role in selecting the right DFT gauge for the job. When it comes to testing coating thickness on flat surfaces, most of the time, it’s possible to get away with a standard instrument setup. However, in case a measurement is taken too close to a sample’s edge, then readings get affected due to the magnetic field reaching beyond a specimen (Figure 3).
Figure 3. Graphical representation of an “edging” effect
In case a sample is small and a probe inevitably always lands near an edge, you can obtain more accurate results by using an appropriate “thin tip” probe. It is also suitable for measurements in intricate locations. Further below you can find two types of “thin tip” probes offered by Helmut Fischer GmbH for measurements on ferrous and non-ferrous substrates (Table 2).
FGA06H-MC probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Mechanical design is especially suited for precise probe positioning (e.g., near edges)
FTA2.4-MC probe. Measures electrically non-conducting coatings on non-ferromagnetic metal substrates. Mechanical design is especially suited for precise probe positioning (e.g., near edges)
Table 2: Tin Tip Probes
The FGA06H-MC probe works with FMP10 deltascope, FMP20 dualscope, FMP30 deltascope, FMP40 dualscope, and FMP100 dualscope. Meanwhile, FTA2.4-MC operates with FMP10 isoscope, FMP20 dualscope, FMP30 isoscope, FMP40 dualscope, and FMP100 dualscope. Follow the link below for more details about the FMP range of instruments and how to access probes’ technical information.
COATING THICKNESS (DFT) GAUGES
Wide range of handheld dry film thickness gauges (DFT) for the measurement of coating thickness on ferrous and non-ferrous substrates
Finally, it’s essential to consider that coating thickness measurements can also take place inside bores and holes. In this case, it’s often impossible to obtain a reading without a specialist probe.
Table 3 demonstrates suitable probes for measurements in hard to read locations.
FAW3.3 probe. Measures electrically non-conducting coatings on non-ferromagnetic metal substrate materials. It is suited for measurements on plane specimens or in pipes boreholes and recesses. It can also be used when surfaces exhibit a damp condition (acidic contamination of test surface).
FAI3.3-150 probe. Measures electrically non-conducting coatings on non-ferromagnetic metal substrate materials. Suited for measurements in pipes, boreholes, grooves, etc. Smallest permissible inside diameter: 9 mm. Maximum insertion depth: 150 mm.
FGABI1.3-150 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Suited for measurements in bore holes, pipes, or grooves. Smallest permissible inside diameter: 9mm. Maximum insertion depth: 150mm
FGABI1.3-260 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Suited for measurements in boreholes, pipes, or grooves. Smallest permissible inside diameter: 9mm. Maximum insertion depth: 260mm
Table 3: Probes for coating thickness measurements in hard to reach locations
Sample Geometry
Most of the time, the final sample geometry may be more complicated with round and concave surfaces, and as a result, the measuring can be problematic. As an example, in the automotive industry, most of the measurements acquired on car bodies are either on a convex or a concave surface.
Sample geometry has one of the most significant impacts on the coating thickness measurement readings, often producing a deviation from the real value (Figure 4). In this case, operators are forced to conduct a re-calibration for every shape. It adds complications to the measurement procedure with increased testing times and a substantially higher room for errors.
Figure 4. Measurement deviations due to geometry
To avoid errors generated from sample geometry, it is possible to use curvature compensation probes. In this way, an accurate coating thickness reading is always obtained, regardless of a specimen shape. Helmut Fischer GmbH offers a list of patented probes for measurements on ferrous and non-ferrous substrates you can find in the table below.
FTD3.3 probe. Measures paint, lacquer, plastic, and anodised coatings on non-ferromagnetic metal substrates. Excellent curvature compensation down to approximately 4 mm diameter shapes. Patented design. It is suited for measurements on curved surfaces such as car bodies
FGA06H probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Uniquely suited for small test areas and curved surfaces. High wear resistance of the tungsten carbide tip. It is not suited for very rough surfaces.
Table 4: Curvature compensation probes
Coating Thickness Extremes
Minimum and maximum coating thickness may require two different probes to acquire accurate results. At the same time, if acquired measurements are to be in the nanometer range, one will need to consider alternative methods, such as micro-sectioning or X-ray fluorescence (XRF).
The further away a probe is from the substrate, the weaker the resulting magnetic field, and vice-versa. As a result, extremely thin coatings of less than 3 microns have a much more significant variation in their measurement data. Here, the signal is too strong for the probe to recognise the difference between the presence and the absence of a coating.
When measuring thin coatings, it is advisable to use a motorised measurement stand. This instrument accessory ensures consistent readings are achieved and eliminates the possibility of thickness deviations caused by manual operation.
Measurement Stand
Motorised and fully automatic coating thickness measurement stand for precise and repetitive results.
Substrate Thickness
Thin substrate thickness can also have a dramatic influence on readings. Measurement distortion happens when the magnetic field reaches beyond the substrate material thickness (Figure 5).
Figure 5. Measurement distortion due to a thin metal substrate
When a substrate is too thin, standard probes may give misleading readings even after a corrective calibration. In these instances, Helmut Fischer GmbH offers a list of high-frequency probes. Their distinguishing feature is that eddy currents are induced in the skin of relatively thin substrates, to allow reliable coating thickness measurements without influence from the variation of substrate thickness.
Final Instrument Choice
The market is saturated with a broad range of coating thickness gauges, so it may initially seem too overwhelming to choose an instrument from the wide range of options available, especially when it doesn’t accurately explain what the right choice is.
In these instances, it may become extremely tempting to go for the cheapest option that the market offers. However, as attractive as it may be, the final decision should always be guided by the coating thickness measurement applications.
At Helmut Fischer GmbH, purchasing a coating thickness gauge isn’t just a matter of Googling online and pressing the “buy now” button, of course. Providing the customer has the right knowledge to make an informed decision; it can become that simple.
Further below two types of gauges are shown, that are offered by Helmut Fischer GmbH – DFT gauges with a built-in probe for straightforward applications and more advanced instruments that can accommodate numerous specialist probes for more challenging measurement tasks.
MP0/MP0R
Simple hand held gauges with a built-in probe for measurements on ferrous and non-ferrous substrates
Recommended article:Function Generators Explained
FMP100/150
Top end hand-held gauges with an interchangeable probes for a wide range of applications
How to Choose Your Right Coating Thickness GaugeThickness Gauge?
We’ve all been there.
The desire and effort put into choosing the right device such as a coating thickness gauge can leave you disappointed and frustrated knowing you’ve given it all you have.
A coating thickness gauge is an essential tool for assessing the quality of a coated component or a piece of equipment like a vehicle. It gives you specific data like how long the vehicle has before corrosion sets in. This kind of information can help you assess the vehicle’s value and consequently allow you to bargain the price more accurately.
This guide contains all the information you need to choose the correct coating thickness gauge, including various applications and typical buying considerations.
Want to know more? Then let’s dive right in.
I. What are the Types of Coating Thickness Gauge?
Coating thickness gauges are sometimes referred to as paint meters. However, their function is to measure the thickness of coating material to ascertain the level of protection of the coated material, often known as the substrate. Interestingly, there are three general categories of coating thickness gauges, including digital, destructive, and mechanical coating thickness gauges, all of which have specific application areas.
Digital coating thickness gauges are often very versatile as inspectors use them to measure almost any material’s coating thickness, including ferrous and non-ferrous materials. They are also very accurate with a repeatable thickness measurement.
On the other hand, destructive coating thickness gauges are suitable for multi-coat paints and non-metallic substrates. However, they are not ideal for risky job areas like underwater or highly flammable environments where mechanical coating thickness gauges are most suitable.
II. What are the Applications for Measuring Coating Thickness?
Measuring the coating thickness on components is often found in different industrial and domestic operations, including
For Typical Coating Materials
These materials include paints, plastic, and enamel.
Insulating Coatings
Paints, enamel, plastics, and ceramics acts as insulating coatings on components that inspectors must check against design requirements.
Non-Ferrous Coatings
include chrome, brass, lead, zinc, and copper.
Ferro-Magnetic Coatings
Electroplated Nickel is a typical example of a ferromagnetic coating.
For Typical Substrate Materials
Includes both insulating substrates and non-ferrous substrates like Tin and aluminum.
Insulating Substrates
Plastics, epoxy, and glass are often used as insulating substrates and need coating thickness gauges to ascertain quality.
Non-Ferrous Substrates
Aluminum, bronze, and copper are typical examples of non-ferrous substrates that require coating thickness gauges.
Ferro-Magnetic Substrates
Using electroplated Nickel for ferromagnetic coatings often requires coating thickness gauges for quality assessment.
For Typical Coating Measurement Application
Different applications require coating thickness gauges, including insulation coatings with materials like paint, plastic, and enamel.
Automotive Refinishing Detection
Finished surfaces in the automotive industry are critical to ascertain the quality and value of the product. A poorly finished surface is seen as having low value.
General Industrial Measurement
Industrial measurement of coatings, especially on metallic substrates, are common, especially in anti-corrosion applications.
III. What to Look for When Buying a Coating Thickness Gauge?
Deciding on the most suitable coating thickness gauge for assessing the quality of coatings can sometimes be challenging. You’ll need a thorough understanding of the inspection requirements. Most importantly, careful consideration of some critical factors and features is essential for this process. Here are the vital elements you should never fail to consider when buying a coating thickness gauge.
- Measuring Range and Accuracy
– Usually, the maximum and minimum thickness measurable by a coating thickness gauge determines its range, and its accuracy is the level of acceptable tolerance for error built into it. These parameters are essential when looking for a suitable coating thickness gauge. The higher the accuracy and range, the better the device though this might also mean a higher price. Typically, the accuracy of a coating thickness gauge often comes as ±(3%+1um) but can change based on the material under inspection
.
- Battery and Power
– Coating thickness gauges get power from different battery types, including AAA and rechargeable batteries. But rechargeable battery-powered devices are preferred for obvious reasons like the convenience and charging options, including USB chargers. Still, other coating measurement devices do not need batteries at all.
- Display
– Different types of coating thickness gauges utilize different types of reading output. While some have a side scale to indicate reading values, others have a display screen for you to see the readings. Though devices with a display screen are better for the sake of easy usage, you need to ensure that the readings displayed on the screen are also easy to read without being crowded.
IV. How to Choose a Coating Thickness Gauge?
Many factors often determine the choice of a suitable coating thickness gauge. However, the type of coating material and the thickness measurement method often dictate these factors’ most critical. You’ll usually be the judge of the most critical factors to consider in choosing any coating thickness gauge for your inspection needs. Here are the essential elements for selecting an accurate coating thickness gauge.
- Measurement Occasion
– The measurement occasion often refers to the flatness and width of the surface. A high-precision coating thickness gauge might be most suitable when these parameters are substantial. On the other hand, smaller objects will only require a general coating thickness gauge with a more general precision that will suffice.
- Size of the Measured Material
– Size matters. And in selecting a suitable coating thickness gauge, the size of the material under examination is an essential consideration. Certain coating measuring devices are ideal for small bolts, screws, and nuts. But when it comes to bigger components, a more convenient coating thickness gauge will be required. You might even need fixtures to make the operation more suitable for massive objects.
- Measurement Range
– Choosing a coating thickness gauge with a suitable measurement range is essent
ial. However, the type of coating on the object will significantly affect the measurement range you will require for a coating thickness gauge. Mostly, a thickness range of 0 – 2000 μm is often acceptable, but for thicker coatings used in an anti-corrosive and fireproof application, a thickness range of up to 0 – 5000 μm might be required.
- Instrument Accuracy –
Depending on your purpose of using a coating thickness gauge, the level of accuracy you require might vary considerably and might also affect your choice of a coating thickness gauge. Generally, home or domestic use of coating thickness gauges doesn’t require the highest level of accuracy, and a cheap entry-level device might be enough. However, industrial usage often requires higher accuracy, and a more specialized coating thickness gauge will be suitable.
- Price
– Your budget is a critical determining factor when choosing a suitable coating thickness gauge. The price a supplier offers to give you a coating thickness gauge will be an essential determiner for making your choice, as your budget is a primary consideration when choosing a coating thickness gauge.
- Ease of Use –
Choosing a coating thickness gauge that is difficult to use can be a deal-breaker when choosing a coating thickness gauge. A more intuitive device with a readable display gives you less stress while measuring the coating thickness. It also makes you more effective and faster while carrying out your inspection. Additionally, a new user will quickly understand how it works without going through rigorous training to use it.
- Data Entry – S
ome coating thickness gauges do not offer any form of compatibility with a computer. As such, you only have the option of entering the data you’ve collected into a sheet of paper or a hardcopy book. However, some manufacturers give you proprietary software that allows you to connect your measuring device with your computer so that you can enter the data you’ve collected directly into your computer.
- Other Considerations
– You might have to consider other factors such as instrument automation, a minimum, and maximum measurable area, minimum measurable curve, and data collection ability of a coating thickness gauge. These considerations are also crucial in choosing a suitable coating thickness measuring device for your peculiar quality assessment needs.
V. How to Perform the Calibration with Coating Thickness Gauge?
Like most devices and equipment used in assessing the quality of a component, the coating thickness gauge has some level of error tolerance built-in. It will often need periodic checks to ensure that this tolerance has not been exceeded. Consequently, you’ll need to perform a calibration process to ensure you keep your coating thickness gauge within an acceptable error tolerance limit.
To perform the calibration of a coating thickness gauge is pretty easy and quick as most manufacturers provide accompanying software that can guide a user through the process.
The first step is to take about 5 to 10 measurements on an uncoated object to determine a zero point for the coating. Then set a calibration foil on the uncoated object and repeat the exact 5 – 10 measurements to get the nominal value as much as the film thickness corresponds to the object’s coating, the better the accuracy of the coating thickness gauge.
VI. What is the Detection Process of Coating Thickness Gauge?
Depending on whether the material under examination is ferrous or non-ferrous, the detection principle of a coating thickness gauge can differ significantly. However, the detection process of a coating thickness gauge is the same regardless of the material type.
The detection process often begins activating the device by pressing a power button or a switch. It might take a few minutes for the device to automatically calibrate itself to its surroundings to get accurate readings, for which you’ll have to wait. Next, set your desired configurations on the device with the appropriate buttons and carefully place them on the object for inspection. When you are set, simply start the operation.
➤ Related Article: How to Check Car Paint Thickness with a Coating Thickness Gauge?
Conclusion
In conclusion, choosing a suitable coating thickness gauge shouldn’t be difficult and frustrating if you know what factors to consider. Depending on the type of material, the risk associated with the work environment, and the level of accuracy you desire, your choice of a coating thickness will often be between a digital, mechanical, or destructive coating thickness gauge. However, the most important consideration you should use in making your choice includes resolution, speed, accuracy, measurement range, and ease of use. Don’t also forget to consider your budget, as this is, in most cases, the most critical factor.
4.9/5 - (59 votes)
How to Choose a Correct Coating Thickness Gauge
The importance of measuring coating thickness is discussed extensively in the “How to Measure Coating Thickness” article. When it comes to selecting a handheld portable coating thickness gauge, an incorrect instrument choice may result in a measurement failure (e.g., inability to obtain a value) or completely wrong results.
Even when a false reading is obtained with an incorrect gauge for the job, there’s also a high risk of assuming it’s accurate.
The above factors increase the chances of failing to meet a desirable coating thickness specification. The consequences may lead to the added costs of rework or lost contracts due to customer dissatisfaction.
This article explores the factors that influence choosing the most suitable gauge for a specific application, first time, and ensure the measurements are fully representable of the actual coating thickness.
INFLUENCING FACTORS
When it comes to choosing a suitable coating thickness gauge, it’s essential to consider several crucial factors. Each one of them will determine what type of instrument and measurement probe are required.
The Physical State of a Coating
Initially, for coatings in a liquid state or the so-called ‘uncured state’, the traditional Dry Film Thickness (DFT) gauges won’t work. For such applications, non-contact powder coating thickness gauges are required. They function by placing the probe at a calibrated distance from a measured surface, and readings are obtained using the ultrasonic measurement principle.
This method is limited to powder coating applications, where a thickness needs to be predicted before the final curing stage. Once the depth is known, it’s possible to potentially reduce the powder consumption that leads to leaner coating application processes with financial and ecological advantages.
However, for coatings is their stable (cured) state, Dry Film Thickness (DFT) gauges are ideal instruments for these applications. They also test layers non-destructively and cover a significantly wide range of applications. In this instance, a measurement probe needs to be applied to a surface for a reading to take place.
This article guides a reader to choose the appropriate DFT gauge for measurements of coatings in their finished “cured” state.
Coating and Base Material
DFT Gauges work using either magnetic induction or eddy current measurement methods. The main difference between the techniques is that the first measures the coating thickness on Ferrous (Fe) while the latter on Non-Ferrous (NFe) substrates. Some gauges incorporate both principles in one to cover all possible base materials. The principle of operation can be seen in Figure 1 and Figure 2.
Figure 1. Schematic diagram of a probe incorporating magnetic induction method.
Figure 2. Schematic diagram of a probe incorporating eddy current amplitude sensitive method.
The magnetic induction measurement method works by generating a low-frequency magnetic field that is produced by excitation current I~. A measurement coil μmeasures the resulting magnetic field.
The Eddy current test method, (amplitude sensitive) measures according to ISO 2360 and ASTM 7091 standards. A coil wrapped around the ferrite core is induced with an excitation current. It generates a high-frequency magnetic field that sends loops of electrical current into a base material, in planes perpendicular to the magnetic field. The same coil measures the resulting magnetic field.
In both methods, the measurement coil sends a signal to the instrument (DFT gauge), which converts it into numerical units we can understand, such as microns or mils.
In case a coating has the same chemical composition as a substrate, there’s no way for a measurement probe to recognise the difference. Hence, it’s essential to understand what material a coating consists of and whether it’s measurable on a given substrate using a DFT gauge.
The table below demonstrates typical applications for both magnetic induction and eddy current methods. We also extensively talk about magnetic induction and eddy current measurement principles in the “How to Measure Coating Thickness” article.
MEASUREMENT PRINCIPLES AND THEIR MAIN APPLICATIONS
Magnetic Induction
Eddy Current
Substrate (Base Material)
Ferromagnetic (e.g., Steel or Iron) μm
Electrically conductive non-ferrous metal (e.g., Aluminium)
The Main Field of Application
– Non-ferromagnetic coatings
– Electroplated coatings made of chromium, zinc, copper or aluminium
– Paint, enamel, varnish or plastic coatings
– Electrically non-conductive coatings
– Paint, enamel, varnish or plastic coatings
– Anodic coatings
Helmut Fischer GmbH offers a wide range of DFT gauges with built-in or interchangeable probes that use magnetic induction and eddy current methods. Learn more about the instruments we suggest following the link below:
COATING THICKNESS (DFT) GAUGES
Wide range of handheld dry film thickness gauges (DFT) for the measurement of coating thickness on ferrous and non-ferrous substrates
Coating Roughness
If a coating is rough, then there will be a higher variation in the measured coating thickness. It happens since a probe tip may rest on peaks or in troughs. Probes that aren’t influenced by rough coatings solve this challenge Figure 3.
Figure 2. A schematic diagram demonstrating how peaks and troughs affect coating thickness readings [A] and the effect of wide and dual-tip probes that take consistent readings on rough surfaces [B].
Wide and dual-tip probes have a larger measurement area and always sit on peaks. This way, the total thickness of a coating is consistently measured. A list of probes offered by Helmut Fischer GmbH, specifically designed to measure on rough surfaces consistently, can be found in Table 1.
FD13H probe. Probes for measurements on virtually all metals. The probes work with two test methods and are therefore able to measure coating thicknesses on non-ferrous metals as well as on ferrous metals. Because of the large pole tip, the probes are also well suited for measurements on rough surfaces.
FTD3.3 probe. This probe utilises the eddy current method. It is suitable for measurements of rough paint, lacquer, plastics, and anodised coatings on Non-ferromagnetic substrates.
V7FKB4 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Higher repeatability precision than single tip probes when measuring rough surfaces.
FKB10 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Uniquely suited for thick layers (up to 8mm). Provide a much higher measurement precision on rough surfaces than single tip probes.
Table 1: Probes for measurements on rough surfaces
The above probes work with the FMP family of instruments. You can learn more by following the link below:
Wide range of handheld dry film thickness gauges (DFT) for the measurement of coating thickness on ferrous and non-ferrous substrates
The Location of the Measurement Area
The location of the measurement area also plays a significant role in selecting the right DFT gauge for the job. When it comes to testing coating thickness on flat surfaces, most of the time, it’s possible to get away with a standard instrument setup. However, in case a measurement is taken too close to a sample’s edge, then readings get affected due to the magnetic field reaching beyond a specimen (Figure 3).
Figure 3. Graphical representation of an “edging” effect
In case a sample is small and a probe inevitably always lands near an edge, you can obtain more accurate results by using an appropriate “thin tip” probe. It is also suitable for measurements in intricate locations. Further below you can find two types of “thin tip” probes offered by Helmut Fischer GmbH for measurements on ferrous and non-ferrous substrates (Table 2).
FGA06H-MC probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Mechanical design is especially suited for precise probe positioning (e.g., near edges)
FTA2.4-MC probe. Measures electrically non-conducting coatings on non-ferromagnetic metal substrates. Mechanical design is especially suited for precise probe positioning (e.g., near edges)
Table 2: Tin Tip Probes
The FGA06H-MC probe works with FMP10 deltascope, FMP20 dualscope, FMP30 deltascope, FMP40 dualscope, and FMP100 dualscope. Meanwhile, FTA2.4-MC operates with FMP10 isoscope, FMP20 dualscope, FMP30 isoscope, FMP40 dualscope, and FMP100 dualscope. Follow the link below for more details about the FMP range of instruments and how to access probes’ technical information.
COATING THICKNESS (DFT) GAUGES
Wide range of handheld dry film thickness gauges (DFT) for the measurement of coating thickness on ferrous and non-ferrous substrates
Finally, it’s essential to consider that coating thickness measurements can also take place inside bores and holes. In this case, it’s often impossible to obtain a reading without a specialist probe.
Table 3 demonstrates suitable probes for measurements in hard to read locations.
FAW3.3 probe. Measures electrically non-conducting coatings on non-ferromagnetic metal substrate materials. It is suited for measurements on plane specimens or in pipes boreholes and recesses. It can also be used when surfaces exhibit a damp condition (acidic contamination of test surface).
FAI3.3-150 probe. Measures electrically non-conducting coatings on non-ferromagnetic metal substrate materials. Suited for measurements in pipes, boreholes, grooves, etc. Smallest permissible inside diameter: 9 mm. Maximum insertion depth: 150 mm.
FGABI1.3-150 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Suited for measurements in bore holes, pipes, or grooves. Smallest permissible inside diameter: 9mm. Maximum insertion depth: 150mm
FGABI1.3-260 probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Suited for measurements in boreholes, pipes, or grooves. Smallest permissible inside diameter: 9mm. Maximum insertion depth: 260mm
Table 3: Probes for coating thickness measurements in hard to reach locations
Sample Geometry
Most of the time, the final sample geometry may be more complicated with round and concave surfaces, and as a result, the measuring can be problematic. As an example, in the automotive industry, most of the measurements acquired on car bodies are either on a convex or a concave surface.
Sample geometry has one of the most significant impacts on the coating thickness measurement readings, often producing a deviation from the real value (Figure 4). In this case, operators are forced to conduct a re-calibration for every shape. It adds complications to the measurement procedure with increased testing times and a substantially higher room for errors.
Figure 4. Measurement deviations due to geometry
To avoid errors generated from sample geometry, it is possible to use curvature compensation probes. In this way, an accurate coating thickness reading is always obtained, regardless of a specimen shape. Helmut Fischer GmbH offers a list of patented probes for measurements on ferrous and non-ferrous substrates you can find in the table below.
FTD3.3 probe. Measures paint, lacquer, plastic, and anodised coatings on non-ferromagnetic metal substrates. Excellent curvature compensation down to approximately 4 mm diameter shapes. Patented design. It is suited for measurements on curved surfaces such as car bodies
FGA06H probe. Measures non-ferrous and non-metallic coatings on steel or iron substrates. Uniquely suited for small test areas and curved surfaces. High wear resistance of the tungsten carbide tip. It is not suited for very rough surfaces.
Table 4: Curvature compensation probes
Coating Thickness Extremes
Minimum and maximum coating thickness may require two different probes to acquire accurate results. At the same time, if acquired measurements are to be in the nanometer range, one will need to consider alternative methods, such as micro-sectioning or X-ray fluorescence (XRF).
The further away a probe is from the substrate, the weaker the resulting magnetic field, and vice-versa. As a result, extremely thin coatings of less than 3 microns have a much more significant variation in their measurement data. Here, the signal is too strong for the probe to recognise the difference between the presence and the absence of a coating.
When measuring thin coatings, it is advisable to use a motorised measurement stand. This instrument accessory ensures consistent readings are achieved and eliminates the possibility of thickness deviations caused by manual operation.
Measurement Stand
Motorised and fully automatic coating thickness measurement stand for precise and repetitive results.
Substrate Thickness
Thin substrate thickness can also have a dramatic influence on readings. Measurement distortion happens when the magnetic field reaches beyond the substrate material thickness (Figure 5).
Figure 5. Measurement distortion due to a thin metal substrate
When a substrate is too thin, standard probes may give misleading readings even after a corrective calibration. In these instances, Helmut Fischer GmbH offers a list of high-frequency probes. Their distinguishing feature is that eddy currents are induced in the skin of relatively thin substrates, to allow reliable coating thickness measurements without influence from the variation of substrate thickness.
Final Instrument Choice
The market is saturated with a broad range of coating thickness gauges, so it may initially seem too overwhelming to choose an instrument from the wide range of options available, especially when it doesn’t accurately explain what the right choice is.
In these instances, it may become extremely tempting to go for the cheapest option that the market offers. However, as attractive as it may be, the final decision should always be guided by the coating thickness measurement applications.
At Helmut Fischer GmbH, purchasing a coating thickness gauge isn’t just a matter of Googling online and pressing the “buy now” button, of course. Providing the customer has the right knowledge to make an informed decision; it can become that simple.
Further below two types of gauges are shown, that are offered by Helmut Fischer GmbH – DFT gauges with a built-in probe for straightforward applications and more advanced instruments that can accommodate numerous specialist probes for more challenging measurement tasks.
MP0/MP0R
Simple hand held gauges with a built-in probe for measurements on ferrous and non-ferrous substrates
FMP100/150
Top end hand-held gauges with an interchangeable probes for a wide range of applications
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