10  Measuring temperatures

10.1  General

To measure a temperature, you can use one or more measurement tools, e.g., a spotmeter or a box. For more information, see section 18 Working with measurement tools .
By using color alarms (isotherms), temperature anomalies can easily be discovered in an infrared image. For more information, see section 19 Working with color alarms and isotherms .

10.2  Achieving a good image

A good image depends on several different functions and settings, although some functions and settings affect the image more than others.
These are the functions and settings that you need to experiment with:
  • Adjusting the infrared camera focus.
  • Adjusting the infrared image (automatically or manually).
  • Selecting a suitable temperature range.
  • Selecting a suitable color palette.
  • Changing the measurement parameters.
  • Performing a non-uniformity correction (NUC).
  • In some situations, you may also want to hide the camera overlay for a better view.

10.2.1  To keep in mind

  • A thermal camera has a resolution limit. This depends on the size of the detector, the lens, and the distance to the target. Use the center of the spot tool as a guide to the minimum possible object size, and get closer if necessary. Make sure to stay away from dangerous areas and live electrical components.
  • Be careful when holding the camera perpendicular to the target. Be observant of reflections, especially at low emissivities—you, the camera, or the surroundings may become the main source of reflection.
  • Select a zone of high emissivity, e.g., an area with a matte surface, to perform a measurement.
  • Blank objects, i.e., those with low emissivities, may appear warm or cold in the camera, because they mainly reflect the environment.
  • Avoid direct sunlight on the details that you are inspecting.
  • Various types of faults, e.g., those in a building’s construction, may result in the same type of thermal pattern.
  • Correctly analyzing an infrared image requires professional knowledge about the application.

10.3  Adjusting the camera focus

It is very important to adjust the focus correctly. Incorrect focus adjustment affects how the image modes work. It also affects the temperature measurement.

10.3.1  Manual focus

You can adjust the focus manually by rotating the focus ring. For more information, see section 21.4.1 Manual focus .

10.3.2  Autofocus

You can autofocus the infrared camera by pushing the Autofocus button. For more information, see section 21.4.2 Autofocus .

10.3.3  Continuous autofocus

The infrared camera can be set up to perform continuous autofocusing. For more information, see section 21.4.3 Continuous autofocus .

10.4  Adjusting the temperature scale

By default, the camera continuously adjusts the image for the best image presentation. Use this automatic mode first, but do not hesitate to adjust the temperature scale of the infrared image manually. For more information, see section 11 Infrared image adjustment .

To adjust the temperature scale, do the following:

10.5  Changing the camera temperature range

10.5.1  General

The camera is calibrated for different temperature ranges. Available temperature range options are dependent on the camera model.
For accurate temperature measurements, you must change the Camera temperature range setting to suit the expected temperature of the object you are inspecting.

10.5.2  Procedure

Follow this procedure:

10.6  Changing the color palettes

You can change the color palette that the camera uses to display different temperatures. A different palette can make it easier to analyze an image. For more information, see section 12 Color palettes .

To change the color palette, do the following:

10.7  Changing the measurement parameters

For accurate measurements, it is important to set the measurement parameters:
  • Emissivity.
  • Reflected temperature.
  • Object distance.
  • Atmospheric temperature.
  • Relative humidity.
  • External IR window compensation.
Emissivity is the most important measurement parameter to set correctly. If the Emissivity is set to a low value, the Reflected temperature also becomes important. The parameters Object distance, Atmospheric temperature, and Relative humidity are relevant for longer distances. The External IR window compensation must be activated if a protective window or external lens is used.
You can set the measurement parameters globally. You can also change the Emissivity, Reflected temperature, and Object distance parameters locally for a measurement tool.
For more information, see section 18.5 Changing the measurement parameters .

10.8  Non-uniformity correction (NUC)

10.8.1  General

When the thermal camera displays Calibrating... it is performing what in thermography is called a ”non-uniformity correction” (NUC). An NUC is an image correction carried out by the camera software to compensate for different sensitivities of detector elements and other optical and geometrical disturbances 4 . For more information, see section 31 About calibration .
An NUC is performed automatically, for example at start-up, when changing a measurement range, or when the environment temperature changes.
You can also perform an NUC manually. This is useful when you have to perform a critical measurement with as little image disturbance as possible. You may, for example, want to perform a manual calibration just before you start recording a video sequence.

10.8.2  Performing an NUC manually

10.9  Hiding all overlay

The camera overlay consists of overlay graphics and image overlay information. The overlay graphics include items such as measurement tool symbols, result tables, and status icons. The image overlay information, which you activate on the Settings menu, provides additional information such as the date, time, and items related to temperature measurements. For more information, see section 8.7.6 Image overlay .
You can hide all camera overlay by touching the soft button icon .