Wednesday, December 12, 2018

What Can I See Through An Infrared (IR) Inspection Window?

Electrical Maintenance Safety Devices, such as Infrared Inspection (IR) Windows, allow for real time, infrared data to be collected on energized electrical assets in a closed and guarded condition. Your company has spent considerable time investigating inspection windows and is considering purchasing and installing them on critical electrical assets. The safety team is researching how to perform an inspection and what data can be obtained from using an Infrared Inspection Window. Let’s investigate!

Simply stated, an IR Inspection Window allows infrared cameras to “see” components and connections inside electrical equipment with the panel covers and doors in place and under fully loaded conditions. Infrared cameras measure the infrared energy emitted by objects which can be equated to an approximation of temperature once some external factors are accounted for. When using an Infrared Window between the camera and the target, the IR window transmission rate must also be factored in to help calculate the target object temperature. Infrared Cameras also take images of the equipment through the IR Inspection Window which allow us to do qualitative comparisons of like components to look for irregularities.

What Can I See?

We learned in the article describing IR Window Lens Material that infrared cameras cannot see through glass or plastic. They require special lens materials that transmit infrared radiation. However, more than just the attributes of the lens material must be considered. When performing an infrared inspection, the thermographer must also consider these critical aspects:

1. Transmission Rate of the Lens Material: transmission rates vary based on type of lens material used as well as the thickness of the lens. The thermographer must know the exact transmission rate to enter into the camera or software setting to obtain accurate temperature data.

2. Emissivity of the Targets: defined as the power of a target’s surface material to emit infrared radiation. Materials are assigned an emissivity value between zero and 1.0. It’s important for the thermographer to know the emissivity value of the surface material he is measuring so he can properly compensate for that material on the IR camera. Incorrect emissivity settings on the IR camera can significantly impact the accuracy of the temperature measurements recorded. Targets with low emissivity values such as copper or aluminum bus should be avoided as they may reflect background infrared radiation and lead to incorrect temperature readings.

3. Field of View of the IR Camera: accurate temperature measurements are obtained when the IR camera has full view of the objects being measured. Any obstruction will compromise the temperatures being recorded. Having an IR Window larger than the diameter of the camera lens is one way to help eliminate errors.

4. Window Field of View (WFOV): to ensure that an IR window of sufficient size is being installed, it is important to know the width and height of the target as well as the depth of the target from the door or panel into which the IR window will be installed. For a simple IR window sizing tool, please click here https://www.iriss.com/fov-calculator/

5. Infrared camera’s operating wavelength: be aware of the operating wavelength of the IR camera (midwave vs. longwave). Make sure your IR window is compatible with the camera wavelength.

6. Number of targets being observed through the IR Window: more than one target can be observed through an IR Window. However, size and positioning of the window on the electrical asset is important. Above all, the thermographer must remember that there are three sources of infrared radiation that are measured by the IR camera: emitted radiation from a target, reflected radiation from a source other than the target or transmitted radiation through an object from a source behind it. The thermographer must determine that his camera is detecting radiation emitted from the target and not measuring reflected or transmitted radiation.

Conclusion:

Infrared Inspection Windows allow for inspections of electrical assets under closed and guarded conditions resulting in time savings, cost savings and improvements in safety procedures. When determining the number of IR windows needed or the size of the IR Window needed for an electrical asset, other critical factors must be considered to obtain accurate inspection data. It’s important for the company to consult with a reliable infrared window provider to insure accurate window selection for the project.

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