Thermal Imager FAQ

While spot infrared thermometers present only a single temperature at a single spot, these Thermal Imaging Cameras give you the whole picture, some up to 19,600 spots! Thermal imaging is the most effective method for finding problems or potential problems in a variety of applications across many fields. 

Thermal imagers allow users to measure temperature in applications where conventional sensors cannot be employed. Specifically, in cases dealing with moving objects (i.e., rollers, moving machinery, or a conveyor belt), or where non-contact measurements are required because of contamination or hazardous reasons (such as high voltage), where distances are too great, or where the temperatures to be measured are too high for thermocouples or other contact sensors. The thermal imagers provide an image, which shows the temperature difference of the object being measured. Hot spots can be seen immediately versus traditional infrared guns, which average the area being measured.

• Solving Electrical Problems
• Detecting Flow of Heat
• Checking Thermal Insulation
• Lubrication and HVAC
• Building Insulation Inspection

There are two ways of using the thermal imager:

1. Either you can read the exact readings of various parts displayed in the display and see what is the temperature of various parts displayed on the screen.
2. Or you can do a comparative study of the displayed picture with another picture of a similar load under similar load conditions.

Some important things to note about thermal imaging cameras.

• Thermal cameras dont directly measure temperatures.  They estimate temperatures based on IR radiation, emissivity of the object, and other factors.   It is fairly easy to fool the camera into giving you bad temperature estimates if you are not careful about emissivity estimates (and a some other issues) -- see below.  Luckily, the emissivity of real world objects is such that useful temperature estimates can usually be made (see below). 
• Thermal cameras give you the surface temperature of the object -- they cannot see into the object.  It can often look like you are seeing into a wall or floor, but what you are really seeing is the influence that a hot or cold element within the wall has on the surface temperature of the wall.  See the heat spreader plate images below as an example. 
• The thermal color images like the one above have very little meaning unless the temperature scale used to produce the image is also provided.  In the case of the image above, the temperature scale is on the right and goes from 65F up to 94.6F and it show the color that maps to all these temperatures.  The exact same image can look very different if the temperature range is changed.  So, if you are looking at an thermal image, always be sure to have the thermal range that was used to produce the image, and make sure that the range makes sense for the parts of the image you are looking at.  The software that comes with the camera can be used to fine tune the temperature range for the pictures. 
• Things that are transparent in the visible light world are not necessarily transparent in the IR world and vice versa.  For example window glazing is transparent in visible light, but nearly opaque in IR light -- so, if you take an IR image "through" a window, what you are really getting is the surface temperature of the window glazing, not the temperatures of the stuff on the other side of the window.   Some things that are opaque to visible light are fairly transparent to IR -- black poly film form instance.

IR radiation can be reflected just as visible radiation is reflected. Shiny metals reflect IR quite well. This can be a problem in that if there are reflections in the thermal image, then what you are getting for those reflection areas is the temperature of the object being reflected and not the temperature of the object you want. You can actually see and identify these reflections if you look for them, but they are easy to overlook if you are not careful.

1. Can take images
2. Can store readings.
3. Take Videos of subjects.
4. Generate Report and Document your observations and inferences.

ONE: Thermal imaging cameras can see below the surface of a target. FALSE

The camera only sees the surface of a target and calculates the temperature from three sources for the total heat energy:

1. Reflected Energy

2. Transmitted Energy

3. Emitted Energy 

This thermal image of a hot water part is derived from infrared radiation detected exclusively from the surface. The camera does not see anything deeper than the surface of the pot. The inside is “seen” only to the extent of a heat footprint created on the surface.

TWO: All types of materials can be easily measured with thermal imaging cameras. FALSE

The temperature information is given in the emitted radiation, but the imager also “sees” the reflected and transmitted components. Most materials are opaque to infrared, so we can usually ignore the transmitted energy .However, many materials (with low emissivity) reflect infrared radiation. Therefore with these materials we must make a “reflected temperature compensation” (RTC)

Consider the two objects above. The tire (left) on the racing car is black, opaque, and non-reflective. The emissivity of rubber is known and we can therefore accurately measure the thermal profile. The objects on the right include highly reflective metallic traffic lights and we must be concerned about reflections of infrared radiation which would, if not properly compensated, result in apparent thermal readings that are significantly inaccurate.

THREE: The color of the target will impact thermal measurements. FALSE

Emissivity is not related to color?The colored labels below are all at the same temperature

FOUR: Thermal imaging cameras should never be used in the daylight. FALSE

Infrared thermal imaging cameras do not detect visible light (see left, response region marked in red).

Below left are two thermal images of my Pembroke Welch Corgi, “Henry”, taken under night and day illumination levels. Both images are virtually the same as the camera only responds to Henry’s long wave infrared signature.

FIVE: The greater the thermal sensitivity a camera has, the better it will work for my thermal applications. FALSE

Thermal cameras with very high thermal sensitivity are quite expensive so it is important to determine the requirements of your applications. In the example below, the temperature difference between the hot spot in the object is at least 10 degrees Centigrade hotter than the rest of the target. For most inspection and engineering applications, thermal sensitivity of .1C is more than sufficient.

SIX: Image fusion and/or visible image capture are required features for a thermal imaging camera. FALSE

Infrared-image fusion is needed by the military for target identification. Under certain low light conditions in the field the image constructed by analog or digital fusion of visible and infrared images has more clarity that either the infrared or visible. However, there is no quantified thermal data in such images. While useful for the military, thermal-visible image fusion is not required for thermal analysis.

Image fusion would add nothing to this application test case as the direct thermal image provides excellent clarity and quantified thermal analysis.

SEVEN: Only highly trained engineers and scientists can properly use thermal imaging cameras. False!!

Training resources are substantial and it has been proven that non-technical personnel can be trained to properly operate/set-up handheld infrared thermal imaging cameras through comprehensive four day classes. Beginner and advanced courses are available throughout the world. It is expected that the use of thermal imaging cameras will be a standard tools for professionals engaged with energy audits, facilities engineering, preventive maintenance, and medical diagnostics.

A higher resolution camera means you will find smaller problems at greater distances. You can find significant problems that could be missed with a lower resolution camera. For example a pc board can have a component, which is overheating. A thermal imager will instantly find the hot spot. 

The critical considerations for any thermal imager include field of view (target size and distance), type of surface being measured (emissivity considerations), spectral response (for atmospheric effects or transmission through surfaces), temperature range and mounting (handheld portable or fixed mount). Other considerations include response time, environment, mounting limitations, viewing port or window applications, and desired signal processing. 

The field of view is the angle of vision at which the instrument operates, and is determined by the optics of the unit. To obtain an accurate temperature reading, the target being measured should completely fill the field of view of the instrument.

FOV, or Field of View, is the largest area that your imager can see at a set distance.   It is typically described in horizontal degrees by vertical degrees—for example, 23º X 17º.    (These “degrees” are units of angular measurement, not to be confused with the degrees of temperature measurement.)  Essentially, it is like a rectangle extending out from the center of your camera’s lens extending outward.  The farther away you look, the larger the rectangle becomes.  Itching for an analogy?  Think of Field of View as the windshield that you are looking out as you drive your automobile down the road. You can see everything from top of the windshield to the bottom, and from the left to the right.

IFOV, or Instantaneous Field of View (otherwise known as Spatial Resolution), is the smallest detail within the FOV that can be detected or seen at a set distance. What does this mean?  It means that at certain distance, you may not be able to see certain small details if your Spatial Resolution is not good enough.  To continue the driving analogy, think of IFOV as the ability to see a roadside sign in the distance (through your windshield).   You can see that it is a sign, but you may not be able to read it when it first becomes recognizable.  IFOV is typically measured in units called milliradians (mRad).   Milliradians are small fractions of an angular degree.

IFOV measurement, or Instantaneous Field of View Measurement (otherwise known as Measurement Resolution), is the smallest detail that you can get an accurate temperature measurement upon at a set distance. Going back to our analogy again… when you see a sign in the distance, and you cannot read it, what do you do?   Pretty obvious, huh?   You either move closer, or you use some type of optical device, such as binoculars, to effectively “bring you closer”. The same is true in infrared thermography.  Assuming that you do not have the power to make the object itself bigger, in order to “read” the temperature measurement more accurately, you usually need to be closer to the object… either physically or optically.  IFOVmeasurement, or Measurement Resolution, is also typically specified in milliradians, and it is often two to three times more than the specified Spatial Resolution.

So what impact does all of this have on your daily thermal imager operation and inspection work?   It means that you need to understand the capabilities of your camera, and work within its physical and optical limitations to see potential problems and to obtain more accurate temperature measurements (when it is important to your application).  If the motor that you are supposed to be inspecting is not within your Field of View, then you are going to need to move so you can see it.   If you are too far away to see the distinct differences between different sets of feeder wires in a lighting control circuit, your thermal images will not do you much good—you’re probably operating outside of the Spatial Resolution capabilities of the camera.  And if you can barely make out the individual feeder wires, you will most likely not be able to get a reasonable temperature measurement because you’re outside of the Measurement Resolution of the imager, too!  Move closer, or put on a lens that effectively does the same thing. 

Infrared imagers, like photographic cameras, can often have different kinds of optional optics and lenses that will allow you to change your Field of View, Spatial Resolution, and Measurement Resolution.   Telephoto lenses magnify the scene and bring you “optically closer”, but generally make the Field of view narrower.   Wide-angle lenses, on the other hand, give you a much wider Field of View, but you may not be able to see the same level of detail.   Telephoto lenses are great for seeing things at a distance, or seeing smaller objects. Wide-angle lenses are excellent for seeing “the big picture” without having to back up. Knowing what kind of lenses are best for specific applications will often save you time, and produce better infrared images for your analysis and reporting.

Sensitivity expresses the ability of an infrared camera to display a very good image even if the thermal contrast in a scene is low. Put another way, a camera with good sensitivity can distinguish objects in a scene that have very little temperature difference between them.

Sensitivity is most often measured by a parameter called Noise Equivalent Temperature Difference or NETD, for example, NETD @ 30 C : 80mK. A Kelvin degree is the SI base unit of thermodynamic temperature equal in magnitude to a degree Celsius, so mK means thousandths of a degree (80mK = 0.080 K).

NETD is defined as the amount of infrared radiation required to produce an output signal equal to the systems own noise. This is a noise rating of the system and should be as low as possible. We are not talking about how loud the system is here!!!  We are talking about electronic noise that we translate into a temperature difference at an object temperature of 30 C (86 F).

The kind of noise we are dealing with is called Temporal noise (of or relating to or limited by time). Temporal noise is the time variation in pixel output values under uniform radiation due to device noise.

You can recognize temporal noise as “snow” in an image, best seen when the temperature span is set to a very small value.

Here is an example of temporal noise

Look familiar? If you look at a dark scene with a camcorder and look at the image, you might see something very similar! The camcorder shows noise at low light levels just like an infrared camera displays it at low temperature levels.

We can graph this noise using a graph called a histogram (a bar chart representing a frequency distribution) which tells us how often certain temperatures appear in the image noise. It looks like this.

Now, if we calculate the standard deviation of the temporal noise, we come up with NETD (area in red).

NETD changes with target temperature. Shown below are two curves, each representing a different temperature range on an infrared camera. You can see that as the object temperature increases, the NETD decreases (better sensitivity). You will also notice that the larger the temperature range, the higher the NETD. The standard for NETD specifications are for an object temperature of 30 C.

So what does this mean for the thermographer? Take a look at the two images below, which one is better?

Its pretty obvious, the image on the left. So a lower NETD number means:Good image – easy to understand

Higher efficiency with a better image (you can work in conditions where a less sensitive camera may not find problems)

Easier to focus the camera

Easier to identify objects in the IR-image

More professional looking reports with better images

Minimum Focal Distance is the minimum distance at which the thermal imager can be accurately used. It is the distance between the object and the thermal imager at which the thermal imager can give precise and accurate picture of the temperature distribution.

Ceramic-like thermal energy sensing material is used to make BST (barium stronium titanate) focal plane arrays, which measure heat by storing it as a fixed value (similar to a capacitor) at each pixel. When the grid of pixels, or focal plane array, is monitored simultaneously, a thermal image is generated.

Because of their fixed-image properties, BST pixels must be refreshed regularly in order to maintain the perception of real-time imaging.

The device used to refresh the image is called a “chopper”. The “blade” of the chopper wheel passes in front of the detector to effectively change the scene temperatures “sensed” with each pass. The speed of the chopper determines the “refresh rate” [Refresh rate (or frame update rate) is the number of times per second that a new image is “created” by the sensor. The refresh rate is determined by mechanical attributes (eg. chopper wheel), where applicable, and the speed of the electronics.] and is typically 30 Hz. 

Thermal imaging cameras have user-selectable multiple color palettes, such as black/white, iron or rainbow. The black/white palette helps identify details on an image, and the rainbow palette has the best thermal sensitivity for displaying the differences in temperature. See sample images below of some color palettes.

It is the number of points available on the screen that can be dragged at desired places to measure “MAX” / “MIN” / “MANUAL” Temperature of that particular spot in real time.

Either all the points can measure the temperature with Global parameters or each point can be defined with emissivity, distance and offset can be adjusted for each point.

There are two lines that can be defined over the entire screen depending on the horizontal and vertical resolution. One Horizontal line and One Vertical line can be defined on the screen and can be adjusted over the entire range of resolution of the screen both horizontally and vertically.

Like the spot measurement, the line measurement mode can be used to measure the temperature with Global parameters or each point can be defined with emissivity, distance and offset can be adjusted for each line.

In this mode the imager provides a maximum of three user definable location squares on the screen of the thermal imager. Each of the three squares measures the maximum, minimum and average temperature in real time.

Again like the Spot and Line measurement, in area measurement as well, the instrument can measure the temperature with Global parameters or each point can be defined with emissivity, distance and offset can be adjusted for each area.

Emissivity is defined as the ratio of the energy radiated by an object at a given temperature to the energy emitted by a perfect radiator, or blackbody, at the same temperature. The emissivity of a blackbody is 1.0. All values of emissivity fall between 0.0 and 1.0. Most infrared thermometers have the ability to compensate for different emissivity values, for different materials. In general, the higher the emissivity of an object, the easier it is to obtain an accurate temperature measurement using infrared. Objects with very low emissivities (below 0.2) can be difficult applications. Some polished, shiny metallic surfaces, such as aluminum, are so reflective in the infrared that accurate temperature measurements are not always possible. 

There are five ways to determine the emissivity of the material, to ensure accurate temperature measurements:

• Heat a sample of the material to a known temperature, using a precise sensor, and measure the temperature using the IR instrument. Then adjust the emissivity value to force the indicator to display the correct temperature.
• For relatively low temperatures (up to 500°F), a piece of masking tape, with an emissivity of 0.95, can be measured. Then adjust the emissivity value to force the indicator to display the correct temperature of the material.
• For high temperature measurements, a hole (depth of which is at least 6 times the diameter) can be drilled into the object. This hole acts as a blackbody with emissivity of 1.0. Measure the temperature in the hole, then adjust the emissivity to force the indicator to display the correct temperature of the material.
• If the material, or a portion of it, can be coated, a dull black paint will have an emissivity of approximately 1.0. Measure the temperature of the paint, then adjust the emissivity to force the indicator to display the correct temperature.
• Standardized emissivity values for most materials are available. These can be entered into the instrument to estimate the materials emissivity value.

Within a user defined area the instrument would be able to inform you the hottest and the coldest spots of temperature.

In the ISOTHERMAL mode, you can define the temperature range and temperature color representation and also define the mode. If you use the “ABOVE” mode and set the ISOmax temperature as 30 Degrees and ISOMin temperature at 20 Degree and change the color to YELLOW, then the areas whose temperature is above 30 Degrees will become YELLOW in color. In the “MED” mode, the areas on the screen whose temperature is between 30 and 20 Degrees will be marked YELLOW and in the “BELOW” mode, the areas on the screen whose temperature is below 20 Degrees will appear YELLOW in color.

In the differential temperature mode, you can either measure the difference in temperature between two points or you can measure the difference in the temperature between the set value of temperature and the temperature of the object that is measured.

To make the instrument various environmental proof, IP test is done. For making any instrument dust or water proof the IP test done is IP-65. If the instrument passes this test then it is completely DUST PROOF and WATER PROOF.

Buy an infrared camera with the highest detector resolution/image quality that your budget allows.

Most infrared cameras have fewer pixels than visible-light cameras, so pay close attention to detector resolution. Higher resolution infrared cameras can measure smaller targets from farther away and create sharper thermal images, both of which add up to more precise and reliable measurements.

Also be aware of the difference between detector and display resolution. Some manufacturers will boast about a high resolution LCD and hide their low resolution detector when its the detector resolution that matters most. 

Find a system with a built-in visible-light camera outfitted with an illuminator lamp and a laser pointer.

Digital photos that correspond to your IR images will help you further document a problem and communicate its precise location to decision-makers. Laser markers show up clearly on visible light pictures.

Select a camera that delivers accurate and repeatable results.

Infrared cameras dont just let you see differences in heat, they let you measure those differences. For best results, look for a thermal imager that meets or exceeds ±2% (or 3.6°F) accuracy. Your thermal imager should include in-camera tools for entering both "emissivity" and "reflected temperature" values. An infrared camera that gives you an easy way to input and adjust both of those parameters will produce the accurate temperature measurements you need in the field to make the best call.

Look for an IR camera that stores and outputs standard file formats.

Many infrared cameras store images in a proprietary format that can only be read and analyzed with specialized software. Standard JPEG with full temperature analysis embedded allows you to e-mail IR images to your customers or colleagues without losing that vital information. Also, look for infrared cameras that allow you to stream MPEG 4 video via USB to computers and monitors.

Consider Bluetooth and Wi-Fi

New test and measurement tools wirelessly transmit vital diagnostic data such as humidity, amperage, voltage, and resistance directly to the camera. The data is annotated automatically to the thermal image and embedded in the radiometric JPEG to support IR findings. Using WiFi and mobile device apps, the ability to send thermal images and IR inspection reports from one part of a facility to another or by email from the field is huge, especially when time is of the essence.

Ergonomic Features

A lighter thermal camera will decrease strain on your shoulder and back during long inspections. Some models have lens systems that tilt along a 120 degree axis allowing users to keep the viewing screen comfortably in front of them. An extra button or two can actually make the camera easier to use as opposed to using one button to step through a maze of menu options. Buttons should be intuitively positioned and comfortable to use. Some cameras offer integrated touch screens.

Picture-in-Picture (P-i-P) and/or image fusion

Allows you to combine thermal and visible-light images for generating reports that are easier to understand.

Reporting Software

Can you create instant reports right from the camera, or on your mobile device with Wi-Fi enabled cameras? Can it perform a wide range of tasks from simple spot measurements to custom radiometric calibrations, or create specialized data analysis using third party software like MatLab™ or Excel?

Temperature Range

A cameras temperature range and sensitivity are important considerations, too. The range tells you what the minimum and maximum temperatures are that the camera can measure (-4°F to 2,192°F is a typical example).

Protect your Investment

Look for cameras with a comprehensive, extended warranty program to protect your investment for the long haul.

Technical Support and Training

The quality of customer service and the depth of technical support available should be integral to your decision on which infrared camera to purchase.