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Thermography


Published on Mar 12, 2016

Abstract

Thermography is a non-contact, non-destructive test method that utilizes a thermal imager to detect, display and record thermal patterns and temperatures across the surface of an object. Infrared thermography may be applied to any situation where knowledge of thermal profiles and temperatures will provide meaningful data about a system, object or process.

Since infrared radiation is emitted by all objects based on their temperatures, according to the black body radiation law, thermography makes it possible to "see" one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature; therefore thermography allows one to see variations in temperature.

Thermography is widely used in industry for predictive maintenance, condition assessment, quality assurance, and forensic investigations of electrical, mechanical and structural systems. Other applications include, but are not limited to: law enforcement, firefighting, search and rescue, and medical and veterinary sciences.

What makes Thermography useful?

1. It is non-contact

-Uses remote sensing

-Keeps the user out of danger

-Does not intrude upon or affect the target at all

2. It is two dimensional

-Comparison between areas of the target is possible

-The image allows for excellent overview of the target

-Thermal patterns can be visualized for analysis

3. It is real time

-Enables very fast scanning of stationary targets

-Enables capture of fast moving targets

-Enables capture of fast changing thermal patterns

Fact…Temperature is the number one form of measurement used in any process control application. As we get better at non-contact measurement and customers gain confidence, the technology will expand. Pressure and flow are also critical measurements as well, but temperature is far and away number one.

Why this technology will continue to grow?

Non-contact temperature measurement is the future. It impacts our lives every day of the week and most of the time we just do not realize it. From INFRARED motion sensors at traffic lights to the infrared motion sensors on our bedroom lighting, airport toilets, automated doors at the local grocery store or the faucets that turn on and off without a touch, infrared sensors impact our lives every day in a very helpful way!

Infrared mechanical scanning technology has been around for years. Line scanner’s and line cameras utilizing this technology have been used for years in small numbers for specific process control applications, rotary kilns, steel and glass production. Two color point radiometers are in use in practically every steel mill in the world although there are a few small corporations who have still not embraced non-contact infrared technology.

Based on studies those hold outs have had some previous bad experience, due primarily to a lack of knowledge of the sales person introducing them to the technological capability of the systems, i.e.: emittance, wavelength, etc. Point radiometers are prolific in every industry. Competition has increased and driven the price down further than ever in the history of the business. This is happening with imaging radiometers now and will continue for years to come.

Infrared Camera System: General Description

Camera systems can be multiple or stand alone. A system can sound an alarm ring a bell or totally control a system. The system configurations differ based on the object wavelength, temperature, (is the object moving or static). How many pixels do you need? Is image quality critical? What is the minimum spot size you need to measure. Each cameras 320 x 240 pixel array gives non-contact temperature measurement at 76,800 points for each camera.

Real time images are transmitted from each camera by an Ethernet board located in each camera. The data is transmitted from each camera by a wireless antennae located on the unit structure and are received by an antennae located on top of the control room. A Cat 5 cable feeds the data to a single PC running real time alarming software. This wireless system reduced the over all system cost by eliminating the need to install conduit and pull wire.

The software allows each camera to monitor numerous locations simultaneously and even integrate these systems into the unit total control PLC. The system can show multiple camera feeds on a single or multiple monitors. Screen choices allow display of data in multiple formats and on user selectable screens. If you want to view camera # 4 simply select camera # 4.

Multiple color scales from white hot to dark cold are available. Viewing temperature over time, histograms, 3-D displays of each image are available at the touch of a finger. Temperature ranges can change automatically and be exported to Excel. Multiple lens options are available as well as enclosure options to fit the environment. Monitoring of these vessels is a safety and process control issue. Outdoor temperatures on the structure can exceed 120 F and we have some systems installed in environments where temperatures reach -40 F.

Thermography is widely used in industry for predictive maintenance, condition assessment, quality assurance, and forensic investigations of electrical, mechanical and structural systems. Other applications include, but are not limited to: law enforcement, firefighting, search and rescue, and medical and veterinary sciences.

Thermography in Broadcasting and Data Communications

Services are offered for the broadcasting and data communications industry. Specializations in trend mentoring and preventive maintenance programs on the following equipments are made:

AM, FM, TV

ATS

UTS

PDU

Advantages:

No cabinets to open, no down time required to de-energize circuit for safety reasons using the Spyglass and Viewport technology

• Reduces loss of revenue due to down time

• Prevents premature failures

• Quickly locates problem, without interrupting service

• Reduces time going to back up generator systems

• Reduces the time spent in low power operations

• Reduces man hours

• Reduces overall operating cost

• Reduces insurance cost

• Increases safety

Important Terms Related to Thermography

Blackbody, Blackbody Radiator -

A perfect radiator, one that radiates the maximum number of photons in a unit time from a unit area in a specified spectral interval into a hemisphere that any body in thermodynamic equilibrium at the same temperature can radiate. It follows that a blackbody absorbs all radiant energy impinging on it and reflects and transmits none; thus a surface with emissivity of unity (1.0).

Field of View [FOV] -

The angular subtense (expressed in angular degrees or radians per side if rectangular, and angular degrees or radians if circular) over which an instrument will integrate all incoming radiant energy.

Focal Plane Array [FPA] -

A linear or two-dimensional matrix of detector elements, typically used at the focal plane of an instrument. In thermography, these are called IRFPA imagers.

Background Temperature, Instrument -

The apparent temperature of the radiant energy impinging on an object that is reflected off the object and enters the instrument. Originates from the scene behind and surrounding the instrument, as viewed from the target. The reflection of this background appears in the image and affects temperature measurements. Good quality quantitative thermal sensing and imaging instruments provide a means for correcting measurements for this reflection.

Background Temperature, Target -

Apparent ambient temperature of the scene behind and surrounding the target, as viewed from the instrument. When the FOV of a point sensing instrument is larger than the target, the target background temperature will affect the instrument reading. Also called surroundings temperature, foreground temperature.











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