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Video-based Fire Detection Systems Used in Metal Recycling

Video-based Fire Detection Systems Used in Metal Recycling Centers

Why do metal recycling facilities catch fire?

The number of metal recycling plant fires has risen over the last few years. An increased amount of lithium ion batteries found in the waste stream may be what is causing most fire incidents.

Recycling centers will receive flammable materials like lubricants, paints, grease, oil, propane, and gas tanks mingled with recyclables. As recycled materials are cut, crushed, compacted, or shredded, traces of flammable substances can ignite when pressure is applied.

With more lithium-ion batteries in consumer goods and an emphasis on recycling, we see more battery waste in recycling facilities. This makes it difficult for facility managers to prevent recycling fires. When lithium-ion batteries are broken or crushed, they can become hot, start to smoke, and start a facility fire. Thus, magnifying an already hazardous condition when added to the scrap metal recycling process.

Devices for Detecting Metal Recycling Fires

There are various fire detection sensors available today that alert recycling managers of fire formation. Different devices have different varying detection timing during the progression of a fire. The following chart shows the relative detectability of fire detection devices at different stages of fire development with corresponding damage levels.

With the number of fire outbreaks increasing in recycling centers, the pressure is on for facility owners. Finding a solution that minimizes fire risks and keeps employees safe is nothing, but a taxing task.

Infrared cameras are the only device to detect a hot spot and show early signs of fire formation. Recycling facility managers are finding that fire alarms and smoke detectors are not giving enough warning time. Having slow response warning systems make it difficult to prevent an industrial fire.

Because of this, industrial and manufacturing centers are beginning to lean towards solutions that use thermal cameras for early warning fire detection. By installing a video-based fire detection system, managers have increased control over industrial fire safety.

Graph of fire progression, showing infrared cameras are the first to detect fire.

How can infrared cameras see fire?

Before forming black smoke or flames, infrared cameras (IR) are the first to detect signs of a fire. IR cameras give employees, first responders, and the fire department enough time to avoid and prevent a fire. Infrared cameras can spot high temperatures at an early stage, serving as a heat detector video surveillance system in your facility.

Calibrated IR cameras can report temperature measurements from specific spots, lines, and areas on live or recorded images. IR cameras are available in different wavebands, pixel resolutions, lens configurations, and communication protocols to meet various installation requirements.

Implementing IoT with Fire Protection Systems

The industrial internet of things (IoT) refers to connected sensors, instruments, and other devices networked into software applications. IoT applications use predictive video analytics and artificial intelligence (AI). These connected networks create systems that can monitor, collect, exchange, analyze, and deliver valuable insights into a system or process.

Fire safety is an area that realizes the benefits of IoT when combined with thermal imaging cameras. With IoT fire alarm systems, safety alerts can be sent to hundreds of people quickly and effectively. Communication options could include voice calls, texts, and emails to targeted recipients to establish quick and effective awareness.

Early fire detection technology can improve emergency planning by using algorithms to prepare better emergency and safety plans.

The system can consider factors such as:

The number of people in the facility.
The location of the fire.
The rate at which the fire is spreading.
The direction of the fire.

This helps prevent congestion by guiding workers to different locations for optimum safety routing.

Video-based fire detection system showing different thermal images of different areas in a facility.

How do metal recycling facilities benefit from installing an infrared video-based fire detection system?

Before early fire detection, material handlers in the waste and recycling industry would unknowingly spread hot materials. Accidently increasing the size of the fire hazard. With fire detection systems that implement early alert notifications, machine operators can avoid problem spots and prevent spreading potential fire hazards.

Fire detection camera systems that leverage IoT are typically less expensive to install and maintain than traditional industrial fire alarm systems. Because the early fire detection software resides in the cloud, there is no need for a dedicated facility computer server. This allows users to access the fire detection system from any device, anywhere, anytime with an available internet connection.

Available communication technology can be added to existing fire detectors, such as smoke alarms, making retrofitting existing systems for IoT easy. By warning earlier on the pathway to ignition, metal recycling center operators avoid costly and potentially life threatening fires.

Sample IoT EFD Configuration for Waste Facilities

Ensure you install a system that meets all your needs!

Industrial and manufacturing facilities benefit when working with experienced fire detection integrators. Experts in the field should thoroughly examine installation sites before designing a detection system. This ensures your fire detection system includes the best fit sensors in the best locations.

Early fire detection IoT systems are easily configurable and can operate in settings beyond metal recycling. Other industrial settings that benefit from infrared fire detection systems include: coal, biomass, industrial laundry, wood processing, trash bunkers, and more.

20+ Page Guide to Fire Detection Systems

Find All Your Answers in Our Guide

Find a reliable fire detection system.
Save money in the long run.
Know the must-have features.
Find a system that adapts to your business needs.
Understand the importance of safety and security.

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MoviTHERM2024-08-16T17:23:05-07:00Thursday, March 21, 2024|Blog|

Coal Pile Monitoring Applications for Fire Prevention

Overview

Companies that store, handle, and transport coal are finding ways to mitigate and prevent fire damage from spontaneous combustion by implementing the Industrial Internet of Things (IIoT) with early fire detection technologies, like infrared cameras.

Heat, oxygen, and fuel are the essential ingredients needed to start and keep a fire burning. In the spontaneous combustion of coal, coal acts as the fuel that, when exposed to air, leads to oxidation, and produces heat.

The general reaction for the oxidation of coal is as follows:

Coal + O2 → CO + CO2 + H2O + HEAT

Suppose the heat generated by the oxidation process is not allowed to dissipate but is retained. In that case, the coal body temperature increases, thus accelerating the reaction rate exponentially, and if not treated, it can result in spontaneous combustion. Studies estimate that for every 18°F rise in temperature, the reaction rate can double.

The oxidation of coal can occur anywhere coal is accumulated and exposed to oxygen. The risk of spontaneous combustion exists at multiple points along the coal supply chain.

Coal Supply Chain

The early detection of hot spots in coal piles is critical if the spontaneous combustion process is to be avoided. Unfortunately, though, detecting early-stage fire formation within a coal pile is difficult. For example, the surface temperature of the coal pile may be near ambient, with internal temperatures being much, much higher. Traditional methods of installing thermocouples can be used but are susceptible to damage during material transport. Spot measurements can also be used but do not detect gradient effects. Monitoring temperature trends over time is generally more helpful in detecting the early onset of coal pile heating with mitigation measures deployed before the situation becomes dangerous.

Coal Supply Chain Diagram

Early Fire Detection using Infrared (IR) Camera Systems
An infrared camera can see areas of warming-up on a coal pile early in the fire development process before forming smoke particles or flames. Even subtle changes in temperature just below the surface show as warm spots in a thermal image. IR camera systems are the first to alert on the pathway to ignition before a coal fire develops.

Pathway to Ignition
IR cameras operate on the heat transfer principle of radiation. The infrared camera has a focal plane array of detector elements that sense infrared light radiated from object surfaces. The radiation captured by the infrared camera detector is digitized, converted to data, and displayed as a viewable image. Calibrated IR cameras can report temperature measurements from specific spots, lines, and areas on live or recorded images. IR cameras are available in different pixel resolutions, lens configurations, and enclosure configurations to meet various installation requirements.

Graph of fire progression, showing infrared cameras are the first to detect fire.

What is IIoT (Industrial Internet of Things)?

The industrial internet of things (IIoT) refers to interconnected sensors, instruments, and other devices networked into industrial software applications that use advanced predictive analytics and artificial intelligence (AI). These connected networks create systems that can monitor, collect, exchange, analyze, and deliver valuable insights into a system or process. IIoT revolutionizes automation by using cloud computing to simplify integration and enhance process control.

IIoT and Early Fire Detection (EFD)

Fire safety is an area that can realize the benefits of IIoT when combined with infrared camera systems. By connecting sensors that alert at different stages of fire development and varying conditions for fire formation, potential fires can more readily be detected and prevented. With IIoT, safety alerts are sent to hundreds of people quickly and effectively. Communication options include voice calls, text, and email to targeted recipients, thus helping create quick and effective awareness. Another advantage to IIoT EFD is scalability. Facility managers can connect multiple facilities into central monitoring and alarming dashboards viewed from anywhere globally. Understanding the situation at all facilities improves the oversight and management of multiple systems from a single control point.

IIoT EFD systems can improve emergency planning by using algorithms to help quickly prepare better emergency and evacuation plans. For example, analytics can consider factors such as the number of people in the facility, facility maps, location of the fire, the rate at which fire is spreading, and the direction of the fire to come up with better evacuation plans. Analytics-based evacuation plans can prevent congestion by guiding workers to different locations for optimum evacuation routing.

Advantages of IIoT EFD with Infrared Cameras are summarized below:

IR cameras can detect fire formation at the earliest stages.
Fast and broad notification to keep workers out of harm’s way.
Cloud-based connectivity and computing minimize hardware requirements.
Automatic software updates keep systems running optimally.
Capability to control external processes, alarms, and extinguishing systems.

MoviTHERM has developed its iEFD solution for coal pile monitoring. This solution integrates fire detection and other monitoring technologies to track temperatures and detect the formation of smoke particles at critical coal supply chain locations. MoviTHERM iEFD alerts the appropriate personnel when temperatures exceed expected limits or when smoke particles are present within the environment.

The following graphic illustrates a sample MoviTHERM iEFD solution for coal pile monitoring.

iEFD IIoT Pile Monitoring Diagram

Conclusion

MoviTHERM iEFD does not replace existing fire detection and response protocols. Instead, the system functions as an early warning system – detecting areas where ignition may occur. New detection methods for heat, smoke, and fire are in continual development and include wireless capabilities that make integration into MoviTHERM iEFD a straightforward exercise. Beyond alarms and notifications, MoviTHERM iEFD uses IIoT connectivity to provide automation controls like initiating and directing an extinguishing system.

Because MoviTHERM iEFD leverages cloud computing, it requires less hardware with a reduced installation burden and cost than legacy detection systems. Available communication technology can be added to existing detectors, making MoviTHERM iEFD retrofitting easy. By warning earlier on the pathway to ignition, those responsible for coal inventory management can avert costly and potentially life-threatening fires before they are permitted to start and spread.

MoviTHERM has installed its IIoT iEFD system for coal pile monitoring and has the expertise to advise facility owners and managers about upgrading existing monitoring systems or prescribing its new iEFD system.

20+ Page Guide to Fire Detection Systems

Find All Your Answers in Our Guide

Find a reliable fire detection system.
Save money in the long run.
Know the must-have features.
Find a system that adapts to your business needs.
Understand the importance of safety and security.

Download Now

MoviTHERM2024-08-16T17:23:13-07:00Thursday, March 21, 2024|Blog|

Biomass Pile Monitoring Applications for Fire Prevention

Overview

Biomass Power Generation facilities are finding ways to mitigate and prevent fire damage by implementing the Industrial Internet of Things (IIoT) with early fire detection technologies, like infrared cameras.

Biomass Power Generation facilities use renewable organic material from plants and animals as a fuel source to generate electricity for industrial and commercial applications. Biomass materials are transported to the generation plant, stored in piles or silos, and burned in a boiler to produce high-pressure steam to drive the rotation of a series of turbine blades connected to a generator that produces electricity. During the storage phase, the biomass materials are most susceptible to fire.

Biomass Pile Monitoring Diagram

Biomass is commonly stored in bulk outdoor piles near the power generation facility. These mounds of material are especially prone to self-heating as they naturally decompose. The decomposition process is accelerated as moisture is introduced from rain and humidity, generating even more heat. As most biomass materials are good insulators, the internal pile heat generated is not allowed to escape and cool, thus increasing temperatures and spreading to a larger internal area. Eventually, the material begins to smolder. Smoldering and flameless fires are more easily ignited than flaming fires and more challenging to extinguish.

The early detection of a bulk pile fire is critical if a biomass fire is to be avoided. Unfortunately, though, detecting early-stage fire formation within a bulk pile fire is difficult. For example, the surface temperature of a pile may be at ambient while the internal temperature could be more than 200°C. Traditional methods using linear heat detection cable can be used but are susceptible to damage during material transport and generally not recommended. Spot measurements are also used but do not detect gradient effects. Monitoring the temperature trends over time is generally more helpful in detecting the early onset of heating where mitigation measures can be deployed before the situation becomes dangerous.

Early Fire Detection using Infrared (IR) Camera Systems

IR camera systems are the first to alert before a fire develops. They see a warming-up of material early in the fire development process before forming smoke particles or flames.

IR cameras operate on the heat transfer principle of radiation. The infrared camera has a focal plane array of detector elements that sense infrared light radiated from object surfaces. The radiation captured by the infrared camera detector is digitized, converted to data, and displayed as a viewable image. Calibrated IR cameras can report temperature measurements from specific spots, lines, and areas on live or recorded images. IR cameras are available in different wavebands, pixel resolutions, lens configurations, and communication protocols to meet various installation requirements.

What is IIoT (Industrial Internet of Things)?

The “industrial internet of things” (IIoT) refers to interconnected sensors, instruments, and other devices networked into industrial software applications that use advanced predictive analytics and artificial intelligence (AI). These connected networks create systems that can monitor, collect, exchange, analyze, and deliver valuable insights into a system or process. IIoT is revolutionizing automation by using cloud computing to simplify integration and enhance process control.

IIoT and Early Fire Detection (EFD)

Fire safety is an area that can realize the benefits of IIoT when combined with infrared camera systems. By connecting sensors that alert at different stages of fire development and varying conditions for fire formation, potential fires can more readily be detected and prevented. With IIoT, safety alerts are sent to hundreds of people quickly and effectively. Communication options include the capability to communicate via voice calls, text, and email to targeted recipients, thus helping create quick and effective awareness. Another advantage to IIoT EFD is scalability. Facility managers can connect multiple facilities into a central monitoring and alarming dashboard. Understanding the situation at all facilities improves the oversight and management of multiple systems from a single control point.

IIoT EFD systems can improve emergency planning by using algorithms and analytics to help quickly prepare better emergency and evacuation plans. For example, analytics can consider factors such as the number of people in the facility, facility maps, location of the fire, the rate at which fire is spreading, and the direction of the fire to come up with better evacuation plans. Analytics-based evacuation plans can prevent congestion by guiding workers to different locations for optimum evacuation routing.

Advantages to IIoT EFD with Infrared Camera systems are summarized below:

IR cameras to detect fire formation at the earliest stages.
Fast and broad notification to keep workers out of harm’s way.
Cloud-based connectivity and computing minimize hardware requirements.
Automatic software updates keep systems running optimally.
Capability to trigger external processes, alarms, and extinguishing systems.

MoviTHERM has effectively deployed IIoT EFD systems for biomass pile monitoring. These systems integrate multiple fire detection and monitoring technologies to track critical temperatures and detect smoke particles at critical locations within the power generation facility. These systems alert the appropriate personnel when temperatures exceed expected limits or when smoke particles are present within the environment.

The following graphic illustrates a sample MoviTHERM IIoT Early Fire Detection solution for pile monitoring.

iEFD IIoT Pile Monitoring Diagram

Conclusion

It is important to note that the system discussed is not designed to replace existing fire detection and response protocols. Instead, the system functions as an early warning system – detecting areas where ignition may occur. Additionally, new detection methods for heat, smoke, and fire are in continual development. Many new detection devices include wireless capabilities that make integration into an IIoT EFD a straightforward exercise. Beyond alarms and notifications, IIoT EFD systems can provide automation controls like initiating and directing an extinguishing system.

Because IIoT EFD systems leverage cloud computing, they require less hardware with a reduced installation burden than legacy detection systems. Available communication technology can be added to existing detectors making IIoT retrofitting of existing systems an easy process. By warning earlier on the pathway to ignition, those responsible for biomass bulk management can avert costly and potentially life-threatening fires before they are permitted to start and spread.

MoviTHERM has installed IIoT EFD systems for biomass pile monitoring in power generation facilities and has the expertise to advise facility owners and managers about how to upgrade existing monitoiring systems or prescribe new IIoT EFD systems.

20+ Page Guide to Fire Detection Systems

Find All Your Answers in Our Guide

Find a reliable fire detection system.
Save money in the long run.
Know the must-have features.
Find a system that adapts to your business needs.
Understand the importance of safety and security.

Download Now

MoviTHERM2024-08-16T17:23:22-07:00Thursday, March 21, 2024|Blog|

What is Infrared Non Destructive Testing and How Does it Work?

Infrared non-destructive testing (NDT) has been around for more than 30 years but has recently gained more momentum.

The momentum is primarily driven by the need for faster inspection times on large aerospace structures. The most widely spread NDT method to date is still ultrasound (UT), but it has its limitations with respect to rapid, large area inspection capabilities.

Infrared non-destructive testing is based on the principle of thermal wave imaging. It is considered an active thermography method, as opposed to a passive method. The active part comes from using an external heat source to warm up the part. Whereas in standard thermography, the camera is usually capturing heat, inherent to the process. For example, when using a thermal camera to check for the temperature of an electrical motor that is in operation.

A passive method does not lend itself very well to an NDT inspection, since the part is typically at room temperature. We call that also being in a state of thermal equilibrium. A workpiece in that state would not create any useful information or thermal contrast when imaged. Hence, the need for an active excitation.

Excitation Methods

The most used methods of excitation for infrared non-destructive testing applications are either a Xenon Flash Lamp or a Halogen Lamp. The flash method is used for “Flash Thermography”. A large amount of energy is stored in a flash generator, on average 6 kilo Joules or above. Upon the start of measurement, the stored energy is discharged in the Xenon flash bulb.

Example of a Flash Thermography System

The discharge happens in a flash in only about 2 milliseconds. This creates a rapid increase of temperature on the surface of the workpiece, which also starts to dissipate immediately. A thermal camera pointed at the part is being used to record a thermal image sequence, thus monitoring the temperature decay on the surface of the part. What happens during this time is that the energy on the surface starts to penetrate the material via a thermal wave. The thermal wave propagates back to the surface and creates a temporal pattern of heat conduction (or the lack thereof).

Infrared Non-Destructive Testing

For example, if the thermal wave encounters a void, the heat flow is slowed down. This manifests itself on the surface during the image recording sequence. Although, this technology can not technically “look into” the part, it indirectly can.

Flash thermography is limited with respect to how deep it can find defects. This is due to the rapid heat discharge. There is another active excitation method that helps overcome this limitation. That method is referred to as “Transient Thermography”. The concept is very similar. The difference is the way the heat is being induced into the part.

Foam Core Disbond

Neither the flash method nor the transient method will ever heat up the part surface to any temperatures of concern. Remember, we are talking about a “Non” Destructive Method. An infrared non-destructive testing procedure only requires a temperature increase of about 8 to 10 degrees Celsius above ambient. This increase is enough for creating enough thermal contrast in the result images.

Download Our Starter Guide

For Infrared NDT Systems

Learn how Infrared NDT works
Learn what type of defects you can find
Learn how large of an area you can inspect
Learn how this method compliments UT inspections
Learn how to save valuable inspection time

Download Now

MoviTHERM2024-08-16T17:23:32-07:00Thursday, March 21, 2024|Blog|

Vibro Thermography NDT Technique

Vibro-Thermography is an active thermography method that uses mechanical vibration to locate cracks. It is considered an active thermography method because this method does not rely on existing heat being present in the part that is being inspected. Vibro-Thermography uses ultrasonic frequencies to excite the specimen. These ultrasonic frequencies are typically in the range of 20,000 to 45,000 Hz or 20kHz to 45kHz. A common excitation source for creating these vibrations is an ultrasonic welder.

Vibro-Thermography belongs to the non-destructive test methods. It is the only one that is not non-contact since the ultrasonic horn or transducer needs to be in contact with the workpiece. During the measurement, these vibrations propagate through the part. If a crack is encountered, the crack surfaces rub together from the vibration. The friction from these vibrations creates a small heat signature that the thermal camera can detect.

Vibro-Thermography Setup

The photo above shows a Vibro-Thermography measurement setup. The setup consists of a high-speed thermal camera, an Ultrasonic Transducer with Power electronics (not visible) and a workpiece.

The ultrasonic transducer is placed onto the workpiece. An ‘H’-style gantry allows the transducer to be lowered with the assistance of a pneumatic motion stage. The pressure for the stage is adjustable and allows for variation of the contact pressure for the transducer. A softer coupling medium is used to avoid scratching the part. The medium used in this example is a piece of aluminum foil.

Upon excitation of the part, in this case, a piece of a brake rotor, any cracks will show up as local increase in temperature. The workpiece is propped up on a couple of pieces of wood to decouple the vibration from the work surface.

Performing vibro-thermography on metal parts typically requires a very fast thermal camera. Fast in this context refers to the integration time of the detector as well as the frame rate of the camera. This is due to the heat conductivity of metals. Any small increase in temperature around the crack surfaces will dissipate within milliseconds.

Cracks covered by the ultrasonic transducer won’t be visible. There is a considerable amount of energy being coupled into the workpiece from the transducer. It is therefore normal to see the area around the transducer to warm up. This warm up is not indicative of a defect or crack, but rather the vibrations and resulting friction between the transducer and the workpiece.

Crack detection on turbine blade.

These two images show a Titanium turbine blade being inspected for cracks. Vibro-Thermography is a very useful method for crack detection. The turbine blade is placed on top of some wood and the ultrasonic transducer is wrapped in aluminum foil.

The image on the right has been artificially post-colored with a thermographic color palette. Cold regions appear in blue and warm regions in orange to bright yellow.

There are two cracks that are clearly visible. One big advantage of using Vibro-Thermography is that even complex-shaped parts can be inspected.

The standard non-destructive test method most commonly used in the industry is dye penetrant testing. For that method, it is required to brush a liquid dye onto the part and let it seep into possible crack surfaces. Then the part is being washed. The dye usually stays in the crack and starts to fluoresce when excited with a UV or black light. The drawback of this method is, that it is time-consuming and messy. Dye penetrant testing also cannot detect sub-surface or buried cracks, as there is no chance for the dye to penetrate into the crack.

Vibro-Thermography is better suited in this case, since it even detects near-surface, buried cracks. It can also detect micro-cracks. The thermal conductivity of the part makes the crack surface light up in the thermal camera image. It also enlarges the size due to the thermal bleed or blooming effect. The heat generated by the crack surface diffuses into the surrounding area of the material, thus enlarging the appearance of the crack size. This in turn helps with the detection of micro-cracks.

Micro cracks in a turbine blade.

This example shows a different kind of turbine blade. This blade had been previously inspected with the dye penetrant method. The cracks found are marked with “S” and some black lines.

After inspecting the same turbine blade with vibro-thermography, the actual level of defects and cracking became apparent. The color palette chosen for these two result images is a grayscale palette. Cracks show up as dark spots.

As can be seen in the result image – especially in the lower image – the turbine blade is riddled with sub-surface micro cracks. This level of cracking could have led to a catastrophic failure of the turbine engine, which would have gone unnoticed using only dye penetrant testing.

Do you have an application for crack detection in metals or other materials? MoviTHERM offers a feasibility study testing service. This allows you to prove this method before investing in a Vibro-Thermography System.

Download Our Starter Guide

For Infrared NDT Systems

Learn how Infrared NDT works
Learn what type of defects you can find
Learn how large of an area you can inspect
Learn how this method compliments UT inspections
Learn how to save valuable inspection time

Download Now

MoviTHERM2024-08-16T17:23:41-07:00Thursday, March 21, 2024|Blog|

Using Infrared Thermography for Battery Inspection

Battery Inspection using Active Thermography becomes more important in order to stay competitive. Manufacturers of lithium-ion Batteries (LIB) are challenged with maximizing battery performance and minimizing costs to keep the adoption of LIB technology economically attractive.

From toothbrushes to automobiles, earbuds to mobile devices, and toys to semi-trucks, lithium-ion Battery technology is finding its way into just about everything. As such, the demand for battery materials, innovation in electrode design, improvements in manufacturing, and optimization of charge density are ever-increasing.

In this article, we discuss how active thermography and non-destructive testing (NDT) can be used for battery inspection at various stages of the manufacturing process to minimize electrode defects, optimize material usage, and ensure product quality.

Lithium-Ion Battery Anatomy

A lithium-ion battery consists of multiple parts with the cell acting as the primary component. The cell is the workhorse of the battery and is comprised of the following materials:

Current Collectors

The current collectors are the two battery ends with positive and negative connection points. These connections points are used for charging (power to) and discharging (power from) the battery.

Cathode

The cathode stores lithium and is the positive electrode made from a chemical compound metal oxide.

Anode

The anode stores lithium and is the negative electrode typically made from carbon.

Separator

The separator restricts the flow of electrons inside the battery but allows for lithium ions to pass back and forth from the cathode and anode electrodes.

Electrolyte

The electrolyte fills between the electrodes and carries the lithium ions from the anode and cathode during charge and discharge.

Battery Inspection Anatomy

Lithium-Ion Battery Operation

The operation of a lithium-ion battery is all about the back-and-forth movement of lithium ions between the cathode (+) and anode (-) electrodes. The ions move in one direction during charging (absorbing power) and in the opposite direction during discharge (supplying power). When the ions no longer flow the battery is either fully charged or discharged.

Charge Phase (Absorbing Power)

During the charge phase, with external power applied, lithium ions will migrate from the positive cathode to the negative anode through the separator and electrolyte. At the same time, electrons will flow from the cathode to the anode, however, unlike the lithium ions, the electrons cannot pass through the separator and take a different path around the outer circuit. Arriving at the anode, the electrons and ions combine. The battery is fully charged and ready to use when no more ions can flow.

Battery Inspection Anatomy

Discharge Phase (Power From)

During the discharge phase, the lithium atoms in the anode are ionized and separated from their electrons. The lithium ions migrate through the separator and electrolyte from the negative anode to the positive cathode. Simultaneously, the free electrons flow from the anode to the cathode electrode via the outer circuit, providing power to an external device like a laptop computer. The ions and electrons recombine at the cathode becoming electrically neutral. The battery is fully discharged when no more ions can flow and needs charging to supply power again.

Battery Inspection Anatomy

Lithium-ion Battery Manufacturing Process

The following graphic illustrates the battery manufacturing process, which includes three major parts: electrode preparation, cell assembly, and battery electro chemistry activation.

movitherm battery inspection battery manufacturing

Battery Manufacturing Process

1. Slurry Preparation:

the active material (AM), conductive agent, and binder are mixed to form a uniform slurry with the solvent.

2. Coating and Drying:

The slurry is pumped into a slot die, coated on both sides of the current collector (Al foil for cathode and Cu foil for the anode), and delivered to drying equipment to evaporate the solvent.

3. Calendering:

The electrodes are compressed by driving through a two-cylinder press. This will help adjust the physical properties (bonding, conductivity, density, porosity, etc.) of the electrodes.

4. Cutting Electrodes:

The ﬁnished electrodes are stamped and slitted to the required dimension to ﬁt the cell design. The electrodes are then sent to the vacuum oven to remove the excess water.

5. Cell Assembly:

After the electrodes are well prepared, they are sent to the dry room with separators for cell production. The electrodes and separator are winded or stacked layer by layer to form the internal structure of a cell. The aluminum and copper tabs are welded on the cathode and anode current collector, respectively.

6. Electrolyte Filling & Formation:

The cell stack is then transferred to the designed enclosure. Manufacturers use a variety of packaging depending on the cell application. The enclosure is ﬁlled with electrolyte before the ﬁnal sealing and completes the cell production.

Battery / Electrode Performance

At a basic level, any factors that impact the travel of lithium-ions between the cathode and anode electrodes within a battery will impact performance of that battery. As such, the design, manufacturing, and operation of a battery should be to optimize ion and electron flow.

Within the manufacturing process there are instances when defects and flaws might be introduced into the battery product. For example, during the Coating & Drying step the forming electrodes become potentially susceptible to the following:

Uneven compound spread/thickness variation
Variation in carbon to polymer binder ratio
Scratches
Air bubbles/blisters

Other performance damaging factors can result from the introduction of contamination particles into the electrode foils. During coating, calendaring, and slitting electrode foils can be exposed to delaminated particles, abraded metallic particles, and dust from the production environment.

The introduction contaminants, defects, and flaws will adversely affect the ion / electron ability to travel within the electrochemical cell and thus reduce battery performance.

Active Thermography for Battery Inspection and Quality Control (QC)

IR Thermography has shown to be an effective non-destructive testing method for QC in multiple industries for various applications. The basic operation of an IR camera is based upon the heat transfer principle of radiation. The infrared camera has within it a focal plane array of detector elements that “see” infrared light radiated from object surfaces. The radiation captured by the infrared camera detector is digitized, converted to data, and displayed as an image that can be viewed in the visible spectrum. Certain infrared cameras are radiometrically calibrated to record and display measurement units. Infrared cameras are available with different sensors and pixel resolutions to see specific infrared wavebands.

Advanced Thermography for Battery Inspection and Quality Control (QC)

Flash Thermography for Battery Inspection

Battery Inspection using active Thermography involves the excitation of the target and has been found to be most effective in the detection of flaws and contaminants of battery electrodes. Flash IR thermography is a form of active thermography where the target is exposed to a flash of thermal energy and the subsequent change in surface temperature is monitored by an IR camera. A thermal wave signal sequence is acquired by a computer with real-time image signal processing and analysis revealing how the thermal energy passes from the surface to the interior of the target. If the target has voids or defects, the thermal conduction paths will be disrupted. These disruptions lead to temperature differences on the surface that are detected by IR thermography.

Flash Thermography for Battery Inspection

In general, an increase in the temperature profile suggests the presence of contaminants and agglomerates, while a decrease in the temperature profile indicates pinholes and blisters.

Another Battery Inspection application uses active flash thermography directly following the cell assembly stage where anode and cathode electrodes are welded together, and arrester tabs are attached. Welds are critical since they determine internal contact resistance which impacts charging times, power output, and heat generation. Additionally, weld strength against wear and fatigue will determine the lifetime of the battery.

By analyzing the heat propagation through the weld with advanced thermography, determinations can be made about the weld structure and electric conductivity. In general, high thermal conductivity indicates good welds that are uniform with good penetration and positive current flow.

movitherm battery inspection performance detractors

Battery Performance Detractors

Conclusion

Battery Inspection and Monitoring electrodes, cells, and batteries along the production path can help identify faults and defects early, allowing for quick production condition adjustment. Identifying product quality issues closer to generation points will reduce scrap, improve product quality, and optimize production costs.

Active thermography has proven to be an effective inline NDT method for evaluating and diagnosing the production of lithium-ion batteries. It can be used to identify the introduction of contamination particles and the formation of defects during the electrode creation stages. Additionally, Battery Inspection using active thermography can be an effective tool for evaluating welds in cell creation and battery packing.

MoviTHERM2024-08-16T17:23:50-07:00Thursday, March 21, 2024|Blog|

What You Need to Know Before Buying an Elevated Body Temperature Screening System

Elevated Body Temperature Screening

This article discusses six topics you need to know before buying a thermal camera. There are so many options out there, it can quickly can overwhelming. Especially when you have no background in using thermal cameras for elevated body temperature screening or “EBT”.

This “6 Things you need to know before buying a thermal camera for elevated body temperature screening” article and accompanying video is intended for readers that are in the research and decision making process. Which thermal camera screening solution is right for me?

I have witnessed about 30 new “solutions” and entire new companies enter the market, just in the past two month alone. There is so much misinformation out there and so many false claims, that I felt compelled to write this article and make this video. The COVID-19 crisis has brought out the best in people and unfortunately also the worst.

A lot of companies are currently investing significant sums of money into technology they do not understand the first thing about. A lot of vendors out there didn’t even know how a thermal camera worked two months ago and are now calling themselves experts.

Elevated body temperature screening (EBT) not only requires an in depth understanding about thermography, but also a solid understanding of physiological effects of the human body. In particular, how the body thermally regulates.

Visit our Youtube channel for more educational video content: https://www.youtube.com/user/movitherm

Some companies promote their solutions as “fever screening” cameras. This is a misleading statement, since no thermal camera has ever been cleared by the FDA for fever screening.

These cameras can merely detect a variation in skin surface temperature. My name is Markus Tarin, and I am the President & CEO of MoviTHERM – Advanced Thermography Solutions.

I have spent the past 20 years developing thermal imaging systems for industry and research. Never before have I seen such a frenzy and unethical business practices when it comes to thermal cameras being offered for elevated body temperature screening.

When I started to learn about thermal imaging technology, back in the 90s, it took a go six months to get a fundamental understanding about the infrared spectrum, heat radiation, conduction, convection, emissivity, reflectivity, transmissivity and all the other fancy physical effects that influence the accuracy of a thermographic measurement.

So I empathize with so many of you out there trying to make an “informed” purchase decision within a very short period of time. Many of you may not even have an engineering background, let alone the ability to interpret technical specifications of thermal cameras. Now add to this the complexity of human physiology and how the body’s thermoregulation may skew the results of an optical instrument used for temperature measurement.

The reality is that you won’t have enough time to properly understand enough about these subject matters to truly make an educated and sound decision. What you are left with, is often the marketing literature of the solution provider. And their whole purpose is to play into the panic and fear around this subject matter to sell you their solution.

I felt compelled to share my knowledge and help educate people on this topic. For that purpose, I have put together six topics and boiled them down to the essentials. Hopefully people will find some value in this. This article is not meant to be an exhaustive “training course” or white paper by any stretch of the imagination. Rather, it is meant to convey some basic concepts to separate the marketing hype from technical facts.

Topic# 1 – How does a Thermal Camera work?

A thermal camera captures the radiated infrared energy from the surface of a solid object. The captured energy is then mathematically converted to a temperature reading. The temperature reading of each pixel of the camera is then being associated with a color, representing a temperature.

The absolute accuracy of a thermal camera depends on many factors. Considering all factors (Emissivity, spatial resolution, detector and system noise, temperature drift etc.), the expected accuracy of these cameras is no better than ±2° Celsius or ±3.6 °Fahrenheit. It technically can’t be better, unless you are placing the thermal camera into a very tightly controlled thermal chamber under laboratory conditions.

This is due to the fact that the image detector in the camera, the lens and the electronics warm up and create a temperature drift. Without active temperature compensation, this drift is a large contributing factor to the achievable accuracy on these cameras. All the cameras that are being offered for elevated body temperature screening are based on microbolometer type detectors.

Micro-Bolometer Pixel

I have to get technical – sorry…

I have seen marketing literature lately, that claim a camera accuracy of +/- 0.5C without the use of an external black body i.e. calibrated temperature reference source. They back up the claim with the fact that the entire calibrated temperature range was optimized for human body temperature, rather than the typical 170C to 350C range of typical thermal cameras. It is true that using a smaller dynamic range potentially helps with accuracy. However, this also requires a higher degree of amplification. With amplification comes additional noise. If the detector has an NETD of 0.05k (50mK) at 30C. The best theoretical accuracy achievable is about 10 times NETD. So 0.05K x 10 = 0.5K or 0.5C, ignoring all other error sources. Typical dynamic ranges of microbolometer detectors require a 14bit analog to digital converter. So, in order to make use of the largely reduced dynamic range, one would have to amplify the signal from the detector. This will also amplify the detector noise and hence will affect the achievable accuracy negatively. None of this helps and none of this deals with the temperature drift problem.

Takeaway: Achieving an accuracy of 0.5C with a microbolometer detector based camera requires one of two things:

Active cooling and temperature control of the lens, the detector and signal electronics, which none of these have OR
Using a external temperature reference source (aka black body, that is stabilized to better than +/- 0.5C)

Topic# 2 – What can a Thermal Camera detect?

A thermal camera can only detect, measure and document the variations of skin surface temperatures.

It cannot detect or diagnose any of the following:

If somebody has a fever or not.
If somebody is sick or healthy.
If somebody has an infection of any kind.
If somebody is contagious or not.

A diagnostic decision can only be rendered by a healthcare professional, using other FDA approved methods (fever thermometer, blood test, viral tests etc.)

A thermal camera used for this application requires an FDA 510k clearance. With such a clearance, it can be used as an “adjunct” screening tool for skin surface temperature measurements. It shall never be used on its own to render any diagnostic decision.

Topic# 3 – How to properly measure elevated body temperature?

Body temperature is correlated closest at the inner canthus/tear duct.
Measuring skin surface temperatures anywhere else in the face, will not work properly.
Eye-wear will obstruct the tear ducts and must me removed
Person should be standing still at a fixed distance to the camera
The inner canthus should be covered by sufficient number of camera pixels to allow for an accurate measurement. (At a minimum 3 x 3 pixels, ideally more)

Topic# 4 – What camera pixel resolution do I need?

The tear duct area is about 5mm. We need at a minimum 3 pixels to cover that region for an accurate measurement.
5mm / 3 pixels = 1.6mm/pixel
Using a thermal camera with 320 pixels, we can capture an image size of 320 pixels x 1.6mm/pixel = 512 mm [~ 20 inches]
Using a camera with 160-pixel resolution, we are left with an image size of ~10 inches.
Therefore, pointing a camera into a crowd to detect elevated body temperature will not work.
Assuming an image size of 5 feet, it would require a thermal camera with >12 Megapixels and these do not exist.

Topic# 5 – Reference Black Body vs. Reference Population

There are two legitimate measurement setups available for elevated body temperature measurement.
One uses an external black body reference to increase the accuracy of the measurement to about ±0.5° Celsius or better.
The other one uses a relative comparison of skin surface temperatures (baseline group)
Both setups are valid and require a manual correction from time to time to account for external factors that are impacting the thermoregulation of the human body.
Thermoregulation is the ability of the human body to keep its inner core temperature stable.
Core body temperature is: 36.4–37.1 °C (97.5–98.8 °F)
The body will either try to conserve energy or try to get rid of excess energy to maintain its ideal core temperature.
This results in increased or decreased skin surface temperatures, as the skin is the
interface to the environment.

Topic# 6 – Which solution can I trust?

Be aware of “ambulance chasers”. More than 30 new solutions and companies have been created in the past two months.
Work only with reputable companies with a proven track record.
How long has the solution they are selling been on the market? Was it successfully used during previous pandemics, such as SARS & Swine Flu?
Be aware of false camera accuracy claims.
Be aware of fully automated systems.
Be aware of low-cost solutions.
Do not buy a solution that claims to be able to scan more than one person at a time. (Crowd scanning).
Be aware of false claims in marketing literature and websites.
(i.e. Fever detection, avoids spreading infection, any diagnostic claims, keeping you safe etc.)
Not all thermal cameras and solutions are created equal!

So, what is an example of a trust worthy solution?

FLIR A320 Tempscreen
Originally developed for previous pandemics, such as SARS, Swine Flu etc.
Installed thousands of times around the world at airports, public buildings etc.
Proven solution, tried and tested.
FDA 510k Clearance for skin surface temperature measurements.
Manufactured by the world’s largest manufacturer of thermal camera – FLIR Systems, Inc.

Would you like to discuss your concerns and questions with me personally? Then go to the Contact Us section and schedule a free consultation today!

MoviTHERM2024-08-16T17:23:58-07:00Thursday, March 21, 2024|Blog|

Infrared Cameras Used for Elevated Body Temperature Screening

The Coronavirus outbreak in Wuhan, China has grabbed the attention of people around the globe. Thermal cameras are being deployed in record time for screening of elevated body temperature at airports and other public places.

However, as useful and capable as this technology is, there is a lot of misinformation circulating in the news. As with the implementation of any technology, there are challenges. It is important to understand the physics involved that affect the accuracy of an optical temperature measurement, but moreover, there are many other factors to consider related to bio-physical phenomena.

Being unaware of how these intricate details is crucially important.

“Knowing what works and why it works can make the difference between having a cool-looking piece of equipment and an effective tool that assists in the screening effort.” – adds Markus Tarin, President & CEO, MoviTHERM

We commonly see thermal imaging system setups that simply point a thermal camera into a crowd. This sort of setup is significantly flawed, when considering all factors that contribute to the accuracy of measuring human elevated body temperature.

More specifically, how skin facial temperature correlates to core body temperature. Based on scientific research (referenced below), the most reliable spot in the human face is the eye canthus.

A small area over the tear duct. The eye canthus is strongly correlated to the inner body core temperature and has been found to the most reliable location on the face.

Image: Courtesy of Ross Overstreet, Flir Systems, Inc.

The image to the left shows the relationship between the camera distance to subject and the measured skin temperature. Two subject were used, a seven year old male and a 44 year old female. Both subjects were imaged under the same conditions.

Moving the camera from 0.5 meter to 6.0 meter away from the subject, resulted in a temperature drop of about 2 degrees Celsius. This is due to the decreasing resolution of the number of pixels projected over the eye canthus, when moving the camera further away from the subject. Compounding this issue is the fact that the standard accuracy of a thermal is only +/- 2 degrees Celsius to begin with. These sort of issues, when compounding would lead to a greater than 50% uncertainty in the screening system at best.

Sufficient number of pixels (spatial resolution) is required for a thermal camera to accurately measure the skin surface temperature. With the limited amount of pixel resolution available, this poses a challenge when imaging a subject, even at a modest distance. Most cameras deployed for elevated body temperature screening have a resolution around 320 x 240 pixels or 640 x 512. This is very low when compared to traditional surveillance cameras. The FLIR A320 Tempscreen camera was specifically designed for this application.

Rather than using a reference temperature source (“black body”), the FLIR A320 Tempscreen uses a different approach to assuring the skin surface temperature measurements are as accurate as possible. For this, the FLIR A320 Tempscreen uses a population baseline. FLIR suggests using about ten known healthy individuals, scan them with the camera and save their readings. All future subjects scanned will be compared to this population baseline.

A better (and necessary) approach to solving the resolution vs. distance challenge is to control the distance to the subject. This is not feasible when pointing a camera into a crowd. The following setup would create a more controlled measurement setup. Since the accuracy of most thermal cameras are only +/- 2 degrees Celsius to begin with, another step has to be taken.

Body temperature screening setup

A calibrated temperature reference needs to be placed in the field of view during the measurement. The reference source, also referred to as a “black body” allows the imaging software to calibrate the scene to a more precise value by providing a higher accuracy reference, than the camera is capable of.

The black body needs to be located at the same distance from the camera, as the face that is being imaged. The active area (heated region) of the black body also needs to be covered with sufficient pixels to yield the desired results. Ideally a pixel cluster of 10 x 10 pixels.

With this approach, temperature measurements of 5 to 10 times the NETD of the camera are possible. Or about +/- 0.5 degrees C. Cameras that support a black body as a reference source are the new FLIR A400 and FLIR A700 Smart Sensor cameras.

This video explains how thermal imaging technology can be used to screen for people with an elevated body temperature. We have seen a lot of misinformation lately from sources claiming that you can simply point a thermal camera into a crowd and “detect” anybody infected with the Coronavirus.

We want to set the record straight and explain the technology in layman’s terms. How thermal cameras work; how you can use thermal imaging to measure skin temperatures and what you can and cannot detect.

There are also several pitfalls and challenges with this technology when it comes to detecting somebody with an elevated body temperature. Things that can affect the accuracy of the measurement are:

Makeup
Physiological Stress
Sweating
Insufficient Camera Resolution
Measuring the wrong location on the face
Not using a reference black body for calibration
Using the wrong camera
Subject motion

… just to name a few.

Related Scientific Research

Below are some research papers that take a deeper dive into the challenges that are being discussed in this video.

Best practices for standardized performance testing of infrared thermographs intended for fever screening. Pejman Ghassemi,T. Joshua Pfefer, Jon P. Casamento, Rob Simpson, Quanzeng Wang. September 19, 2018

International travels and fever screening during epidemics: a literature review on the effectiveness and potential use of non-contact infrared thermometers. Bitar D, Goubar A, Desenclos J C. Euro Surveill. 2009.

Comparison of Infrared Thermal Detection Systems for mass fever screening in a tropical healthcare setting. M.R. Tay, Y.L. Low, X. Zhao, A.R. Cook, V.J. Lee ,Public Health, 2015.

Infrared thermal imaging of the inner canthus of the eye as an estimator of body core temperature. Teunissen, L. P. J., & Daanen, H. A. M. (2011). Journal of Medical Engineering & Technology.

Disclaimer

No products or solutions offered, promoted, marketed or sold by MoviTHERM, without limitation, are intended for any medical or health-related use on humans. (Collectively, the “offerings”). No offerings, whether verbal or in writing, without limitation, are approved by the US Food and Drug Administration or any other governmental agency to diagnose, treat, cure or prevent any disease, including, without limitation, any use for temperature measurement in humans. Any customer, reseller, integrator, agent, representative, end-user or operator (collectively “Customer”) further acknowledges and agrees that, should Customer engage in any Health-Related Uses, Customer shall be solely responsible for ensuring compliance with the applicable laws and regulations, including, without limitation, the Federal Food, Drug, and Cosmetic Act and the regulations promulgated thereunder by FDA, for the use of any Product for the Health-Related Uses and for obtaining and maintaining any approvals, clearances, licenses, registrations, or permits required by FDA or any other governmental authority for the use of any Product for the Health-Related Uses.

MoviTHERM2024-08-16T17:24:06-07:00Thursday, March 21, 2024|Blog|

Seal Inspection Using Thermal Cameras in Your Process Line

Many packages for food, medical, pharmaceutical, supplies and other goods are packaged in bags that are being sealed using heat. Thermal bag seal inspection refers to using a thermal camera to inspect the heat signature of the bag seal, immediately after sealing.

There are several different methods of how the bag seal is being heated, but ultimately all lead to the same result. Two materials are being joined together forming a (hopefully) tight package seal.

How is a thermal seal created?

Thermal bag sealing or package sealing refers to a sealing concept that either heats up plastic materials to their melting point, thus allowing the materials to fuse together. Some package seal designs have a predetermined adhesive area to form the seal.

Induction Sealing of Bottle Caps

This method is commonly used in bottle cap applications. In case of the bottle cap seal, a liner is being inserted into the cap, prior to capping the bottle. The liner may be an aluminum foil or contain a layer of cardboard. The liner is coated with an adhesive that is facing towards the bottle. After the cap has been screwed onto the bottle, the bottle travels underneath an induction heater. The aluminum foil is now being heating by the eddy currents generated in the magnetic field of the coil of the induction heater while the bottle travels down a conveyor. The aluminum foil heats up and melts the adhesive. The pressure from the torqued cap assured that the cap liner adheres to the bottle after the adhesive has cooled down.

Platen Heat Sealers

Another common heat-sealing method is using heated plates. These plates are formed in the shape of the package seal area. Typical package designs are cups or containers with a plastic foil on top. The packages come down a conveyor line and the heated plate sealer pressed down onto the top foil transferring its heat into the package seal area.

Band Sealers

Band sealers are often found in continuous bag sealing applications. These allow the bags to be in motion during the sealing process. The bag is moved through the band sealer while the sealer transfers heat onto the bag seal.

Ultrasonic Sealers

Another common sealing technology for bag sealing uses ultrasound to create heat directly in the seal. This is commonly found in paper bag applications. Since paper does not melt together, an adhesive layer has been applied to the bag seal during the manufacturing process of the paper bag. The paper bag is then being inserted into the jaws of the ultrasonic sealer. A short burst of very powerful ultrasound energy is induced into the bag seal area. This causes the adhesive-covered bag seal areas to vibrate. The friction together with the vibration creates heat, which in turn melts the adhesive and forms the bag seal. All of this happens in a fraction of a second.

There are other bag sealing and package sealing methods and technologies besides these. For example Friction welding, Radio Frequency (RF) welding, and Laser welding to name a few. The previous examples are just some common examples found in the packaging industry.

The Need for Inspection

First off, not every package seal is critical. Therefore, not every package sealing application requires rigorous inspection.

Thermal imaging-based inspection systems are suited for critical packaging applications. Critical applications are applications in which a weak seal, an impartial seal, or even a small leak would lead to significant issues.

Sometimes these issues are related to product quality and have cosmetic reasons, other times the risk is much higher, such with maintain sterility in medical applications.

Thermal bag seal inspection offers a unique advantage, as it is a non-contact temperature measurement method.

However, based on the thermophysical properties of the materials used for the bag seal, the inspection can be challenging. Some materials are not suitable for thermal imaging-based inspections at all, such as certain metal films which may be highly reflective in nature. Even if the package material does not look very shiny to the human eye, it may still be problematic to inspect with a thermal imaging camera. This all comes down to physics and material properties, emissivity, transmission and reflection.

“It is for that very reason, that we here at MoviTHERM always start every bag seal application with a feasibility study. That allows us and our customers to properly evaluate how the materials behave in the infrared spectrum and whether the inspection application will work, before investing a lot of time and money.” – adds Markus Tarin, President & CEO, MoviTHERM

The Importance of the Inspection Location

Every thermal bag sealing application behaves differently and is sometimes unpredictable. Even if it has been determined that the thermophysical properties of the bag seal allow for reliable temperature measurement, there are still other challenges that need to be tackled. Depending on the level of heat input, the sealing temperature, as well as the physical mass in the sealing area and heat conductivity of the material, the heat in the seal, will spread at a different rate.

Thermal image time sequence of heat seal.

The above pictures are thermal images taken from an ultrasonically welded seal. This time series illustrates how the thermal signature of the weld area changes over time. The first image (t=0 sec) has been taken immediately after the weld. In the last image (t=3.0 sec) you can see that the heat signature has significant changes.

Why does this matter?

Well, the more time passes from the time heat was induced into the bag seal, the more the heat signature diffuses. A side effect of that thermal diffusion is that the heat signature of the seal washes out and becomes very blurry. The heat energy from the hotter regions flows towards the colder regions.

So, if there is an area in the seal that wasn’t sealed properly, it tends to be colder than the surrounding regions. The thermal contrast this creates can be used to detect the defect in the bag seal. However, that thermal contrast starts to fade away, making the defect detection less reliable as time passes.

Application Story – Paper Bag Seal Inspection

To put all of this into context, let’s take a look at a real-world bag seal inspection application. The following example used a thermal camera and custom-developed thermal imaging software. The paper bags are being sealed with an ultrasonic sealer. Once sealed, the bags are being dropped onto a conveyor belt. A proximity sensor detects the bag and triggers the thermal camera. The thermal imaging software analyzes the heat signature of the bag and determines whether the seal is good or bad.

Paper pouch sealing setup.

The photo above shows the test setup. Visible are the ultrasonic bag sealer, the conveyor belt, the paper bag with the seal facing forward, the FLIR Thermal camera, and an industrial PC running the custom thermal bag seal inspection software.

Thermal Bag Seal Inspection – Conceptual Setup

The following illustration shows the setup that was used for the inspection setup. A proximity switch was used to trigger the thermal camera always at the right time after the sealing process.

Paper Pouch Seal Inspection Setup – Conceptual

Determining the right time window for snapping the thermal image of the seal is crucial. Sometimes it actually takes some time for the heat to rise to the surface of the material. So taking the image either too early or too late will not yield satisfactory results.

The black and white image series is a thermal time series. We essentially stopped the conveyor belt. We then extracted six thermal images of the bag seal. The first image at t=0 sec, then t=2 sec, t=5 sec, t=8 sec, t=12 sec and the last at t=15 seconds.

The thermal signature of the seal between 0 to 5 seconds after sealing is still nicely pronounced. This seal is made up of two horizontal lines. Starting with image four (t=8 sec) the double line feature is starting to bleed.

Performing any meaningful thermal image analysis after 5 seconds will become very challenging.

This test helps us to determine where to place the thermal camera with respect to conveyor speed and the material-dependent behavior of this particular paper bag sealing application.

Paper pouch seal image sequence.

Pass-Fail Detection with Respect to Inspection Location

The temperature equalization from warmer regions to cooler regions can result in a bad seal eventually appearing to be a good seal. This thermal equalization effect is graphically illustrated in the 3 images on the right. In a thermal bag seal inspection application, it is important to capture the image soon after the seal is applied.

The sooner the exposure, the more likely the inspection can catch the faults – before equalization can hide them. The light red regions represent the heat signature on the bag seal area that is above a certain temperature threshold.

The detected gap is a faulty seal area where there is insufficient heat present. This would lead to a broken or incomplete seal and may cause product to leak out or moisture to creep into the product.

Correctly understanding this thermal diffusion effect makes the difference between being able to properly identify sealing defects or not.

Pass-Fail Detection

Good Seal Example

The example image below shows a thermal image (vertical seal orientation) and the corresponding processed image. A common machine vision processing step, called “image threshold” was applied to create a blob image. A blob image is a binary image with all pixels turned on that are above a certain threshold. The threshold in this example is directly related to the seal temperature.

What one would expect from a good seal is a continuous red area in the shape of the seal. Additional evaluation functions can be applied to further examine the quality of the seal. For example, one could measure the width along the sealing region and the length. Other options are looking for any orphaned blobs of disruptions.

The inspection strategy mainly depends on how the material behaves and how repeatable the results are. This is also impacted by dynamic behaviors of the sealer. During startup, the seal temperature may still be changing as the sealer warms up.

Good seal example.

Faulty Seals Example

Depending on the application, there are several failure modes. It is good engineering practice to characterize the different failure modes to properly understand how these impact the heat signature of the seal.

Infrared image examples of faulty seals.

Common Challenges in Thermal Bag Seal Inspection Applications

There are plenty of challenges with thermal bag seal inspection applications. These stem from the sealing methodology, the thermophysical properties of the material, ambient and environmental conditions, and dynamic behaviors.

The list below is a summary of commonly encountered challenges in bag sealing applications:

Specific Thermal Conductivity (Rate of thermal diffusion)
Emissivity (Ability of the material to radiate heat)
Reflectivity (Low emissivity surface, reflections)
Transmissivity (Certain coatings and thin film plastics)
Motion blur due to fast moving parts
Aspect Ratio of sealing area vs. sealing width (Resolution problem)
Ambient Temperature fluctuations
Process drift (Start up, dynamic conditions etc.)

MoviTHERM2024-08-16T17:24:19-07:00Thursday, March 21, 2024|Blog|

Flash Thermography NDT Technique

Flash Thermography is an active thermography method for the non-destructive evaluation of materials. Non-destructive evaluation (“NDE”) or non-destructive testing (“NDT”) are often used interchangeably. Flash thermography is considered an active thermography inspection method, because the part under test is commonly at ambient temperature. Examining the part with a thermal camera would not produce any contrast in the image, since there are no significant temperature differences across the part surface. In comparison, using a thermal camera to “passively” look at an electrical motor would yield a high degree of thermal contrast in the image, due to the self-heating of the motor during operation.

Example of a Flash Thermography System

A flash thermography system uses its own heat source to induce heat into the part. This is done to allow an active examination of the thermal behavior at the surface of the part. The “flash” part of a flash thermography system in this case, is considered the excitation source. The flash lamp creates a short, high-energy heat pulse which is directed at the surface of the part.

The flash duration is often on the order of 2 milliseconds or less. The objective is to illuminate and therefore heat the part surface captured by a thermal camera as evenly as possible. The thermal camera records the changes in surface temperature by capturing a thermal video, consisting of many image frames. The software of the flash thermography system then post-processes that thermal video sequence and performs complex math on a pixel-by-pixel basis. The created thermal wave penetrates the part in depth and travels back to the surface, which is being observed by the camera.

In a homogeneous region of the part with no defect, heat travels at the same rate. However, an area with a defect, such as a delamination, void or foreign material inclusion, disturbs the thermal wave on the surface. These temporal changes or differences of the thermal wave are being converted to contrast changes in the result image. Different mathematical algorithms have been developed to accomplish this. Some work better for fast responding materials, such as metals, and others work better for materials that don’t conduct heat very well, such as carbon composites or plastics.

Example Configurations of Flash Thermography Systems

The photos below show different configurations of flash thermograpy systems. From left to right: The first photograph shows a high-end system that was developed for a military application. All systems components are integrated into military style flight cases. That particular system was equipped with six flash generators (blue devices). Each generator delivers 6 kJoule of flash energy for a total of 24 kJoule. The photo next to it shows a combination flash thermography system with transient thermography capability. That system is integrated into a standard flight case with casters. The photo to the right shows a FLIR camera on a tripod next to a flash lamp on a tripod. The setup was used to inspect aircraft propellers for defects. The photo on the very right shows a result image from one of the propellers with an edge defect – a delamination.

flash thermography system millitary MoviTHERM flash thermography system in flightcase flash thermography of propeller blades flash thermography result of propeller blade delamination

How is a flash thermography measurement performed?

The following video shows an overview and demonstration of our flash thermography system. For this demonstration we were using a pre-impregnated (“Prepreg”) carbon composite sample with three plies. Inside the sample there was a triangular piece of poly-film to simulate a defect or foreign object (“FOD”). This is a very typical scenario in today’s composite manufacturing industry. Smaller pieces of poly film sometimes get stuck or left behind from the backing material of the prepreg. The leftover piece of the peel-ply then becomes part of the carbon-composite layup or sandwich. Depending on the size of the FOD, this may lead to structural issues in the finished part. This is especially true for carbon composite structures that are exposed to high-stress. These pieces of peel-ply typically go unnoticed until much later, when the finished part is undergoing a final non-destructive test regimen, typically with ultrasonic testing. Detecting FODs this late can become very costly, as some parts may have to be scrapped.

Flash Thermography on the other hand, can be applied to the uncured prepreg and provides a quick verification of the layup prior to curing the part. Typically, a flash thermography system can detect FODs to about three plies deep. The heat injected into part from the flash is negligible and will not start the curing process prematurely.

A measurement only takes a couple of seconds, as can be seen in the video. This process can be further automated for larger and curved parts, using a collaborative robot and some of MoviTHERM’s automated image processing solutions.

Flash Thermography is very well suited for surface and near surface defects. However, it is very depth limited in materials that do not conduct heat very well, such as composites. The maximum penetration depth is typically around 1.5 to 2 mm for such materials. If the material thickness exceeds 2mm, we recommend switching to a transient thermography solution instead.

Signal Processing – The key to achieving good results!

The photo below shows a result image of a flash thermography measurement. The sample is a carbon composite coupon with flat holes of different depth. Two cursors have been placed on the image to measure temperature vs. time. The red cursor has been placed (baseline) over a non-defective area. The corresponding graph is blue. The green cursor has been placed over a “void”, represented by a flat hole. The graph color for this cursor is orange.

At time time zero, the flash introduces a sharp rise in temperature over the non-defective area as well as over the void. When the part starts to cool off, the orange graph clearly departs from the blue, indicating a different cooling behavior. The two graphs meet again when the part has reached equilibrium around ambient temperature. The difference in the rate of cooling is being exploited with an advanced signal processing technique. In fact, our Flash Thermography system offers several signal processing algorithms to choose from. The signal processing math is applied to every pixel in the image for the entire recorded video sequence.

Areas with different cooling behavior will be converted into a different gray level, resulting in a change in contrast and brightness for non-homogeneous areas in the material. The graph below only demonstrates the signal for two pixels in the image for a simplified illustration. The Y-axis in the graph area calculated units and not temperature. The X-axis are the number of images recorded.

Flash Thermography Temperature Decay

How large of an area can be inspected?

When determining the size of the inspection area, several things need to be considered:

a) The spatial resolution of the thermal camera
b) The size of the flash lamp and the area it can uniformly illuminate
c) The geometry of the part

Spatial Resolution of Camera vs. Smallest Defect Size

The available number of pixels of the camera are being projected onto the part surface. These are contained within the field of view of the camera, which determines the size of the inspection area. For example, a camera may have a detector with 640 x 512 pixels. Any given defect needs to be covered with a minimum of 3 x 3 pixels, ideally more. If the smallest defect size of concern is 0.25″, this would result in 0.25″/3 = 0.08″/pixel. If we multiply this by the horizontal camera resolution, we get the total area we can inspect in one measurement. 0.08″/pixel x 640 pixels = 51.2″. For the vertical size of the field of view, we take 0.08″/pixel x 512 pixels = 40.96″. So the largest field of view size for a single measurement can therefore be ~50′ x 41″.

This is a rather large area. However, we also need to be concerned with how large of an area our flash lamp can cover and produce a uniform heat rise. This may require 2 to 4 flash lamps. With a single flash lamp we can reasonably achieve about 14″ x 12″.

Part Geometry

The part geometry also plays an important role when considering the total size of the inspection area. Curved surfaces can lead to non-uniform illumination of the flash light as well as reflections. Parts with complex geometries may require multiple smaller inspection regions compared to flat surfaces.

Depth Limitation

There are two depth limitations to consider. The first is a limitation due to thermal conductivity of the material. For example, a carbon composite material does not conduct heat very well. A flash lamp discharges all of its energy within 2 msec onto the surface of the part. A purely conducting (heat) material will prevent the thermal wave from penetrating the part very deeply. A rule of thumb is that flash thermography is limited to about 1.5mm to 2.0mm in penetration depth.

The second limitation comes from a ratio of the defect size to its depth in the part.

Depth limitation (diameter/depth) = ~1.4

The 1.4 factor does not consider any advanced signal processing techniques being applied to the result images. So this ratio can be improved to 1.0 to 1.2, depending on various factors. What this ratio says is that the diameter of the defect needs to be at least as large as its depth. However, as we have learned, the penetration depth for flash thermography is often limited much sooner by the thermal conductivity of the material. However, in order to inspect for defects in composites that are located deeper than about 2mm, we can utilize transient thermography instead. Transient thermography allows us to overcome this depth limitation. Another alternative to Flash Thermography is Lockin Thermography.

Example Flash Thermography Application

Defect coupon with flat holes

This is an example application of a flash thermography inspection. The image on the left shows a sample coupon. There are several flat bottom holes drilled into the coupon with varying sizes of diameter and depth. This is a typical test and verification coupon to make sure the flash thermography system is working as expected. It is always a good practice to validate the system with a known standard, before proceeding to inspect critical parts.

The image on the right shows the results from the flash thermography measurement. The holes show up as dark circles. Some of the more shallow ones fade out and some do not show up at all anymore. The ones that do not show up are deeper than about 2mm and exceed the penetration limit of a flash thermography method.

Do you have parts that could benefit from a flash thermography inspection?

MoviTHERM offers NDT Feasibility Studies to help our customers evaluate their application challenges and how well an thermal, infrared non-destructive test method will perform. Learn more about our feasibility study offering!

Download Our Starter Guide

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Learn how Infrared NDT works
Learn what type of defects you can find
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MoviTHERM2024-08-16T17:24:28-07:00Thursday, March 21, 2024|Blog|

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Infrared Cameras

Enclosures

Pan-Tilt Units

MoviTHERM I/O Series

Black Bodies

Discover the Power of Thermography!

Articles, Videos, and More

Our Blog

The Thermal Review Podcast

Newsletters

MoviTHERM's YouTube Channel

Guidebooks, Webinars, & More

Support Articles

Our Expertise

Feasibility Studies

Problem Solving

Commissioning & Training

About MoviTHERM

visit our youtube channel

For Product & Solution Demos

Follow Us

About MoviTHERM

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