Why Is Transmissivity Important When Using Infrared (IR) Windows?

As the head of the Maintenance and Reliability Team at your company, one of your responsibilities is to train the team on new and innovative products and technologies. Your company recently adopted a condition based maintenance program that uses Infrared (IR) Windows. For the next team training seminar, you are going to discuss Transmissivity and the important of this concept as your team performs inspections of your energized electrical assets.

Transmissivity is defined as the ability of radiation to pass through an object. Infrared inspection windows have become an industry standard in infrared electrical inspections of energized equipment increasing both the safety and efficiency of the inspection process. Commercial IR window optics can vary in material but are generally manufactured using either crystals or polymer. The inspector absolutely must know which optic is used in the windows that he will inspect. Why.?

Different optic materials will have different transmission rates. Windows with crystal optics will have different transmission rates than windows with polymer optics. Windows using the same optic will have different transmission rates if the optic is of different thicknesses from one window to the next. It’s critical that the inspector know the transmission rate of the window being inspected to insure the accuracy of the inspection data being collected.

                                                            Transmission Stability and IR Windows: The Effects of Transmissivity on Data Accuracy

What will the inspector do with the transmission rate of a window? For accurate temperature readings, the inspector must enter the correct transmission coefficient into the infrared camera’s settings to obtain the final temperature data for targets behind that window, Failure to accurately compensate for actual transmission can lead to significant errors in temperature readings.  If inaccurate data leads the inspector to a false negative conclusion on the health of an electrical asset, it could result in an expensive catastrophic failure and safety risk to the company.

An inspector may wonder why window manufacturers do not label their window with its transmission rate. A window’s transmission rate is only accurate at a specific wavelength. In the field, many different types of IR cameras are used. The detector in the infrared camera being used may use a wide band of infrared wavelengths rather than a single wavelength. Also, different cameras have variable sensitivities along the infrared spectrum meaning that your camera might be more or less sensitive if the window had a published specific wavelength label. Another consideration is that transmission values of the optic may change over time, especially if the optic is made of crystals which is known to drift due to water and other contaminant ingress into the crystal structure. By contrast, polymer optics maintain a fixed and stable transmission rate over time. These are a few of the reasons why an IR window does not have a published transmission value.

How do inspectors calculate the baseline transmittance of a window? Prior to installation of the IR window, its transmittance value should be determined. The preferred method is to calibrate the camera using an IR window and a target that has demonstrated a stable temperature reading in the range you anticipate your actual target’s temperature would be in normal operating condition. Using that transmission coefficient in that camera for future inspections with that window will provide confidence that the temperature readings of the target asset are accurate.


Transmissivity of an IR Window is a critical data point when using IR cameras to inspect energized electrical assets. The transmission coefficient value of the window must be programmed into the IR camera to determine accurate temperature readings of a target. Failure to enter the correct transmission coefficient value into the IR camera could result in accurate temperature readings that could mask a deteriorating electrical asset and could lead to catastrophic outcomes.

Wireless Temperature and Humidity Monitoring 2019 Image

Wireless Temperature and Humidity Monitoring 2019

The Delta-T Alert™ System monitors and reports critical temperatures within your electrical enclosures daily and effectively tracks your electrical system enclosure temperatures and sends data for analysis and trending. If a critical issue arises, immediate notification allows for an appropriate corrective action long before costly damage occurs. The system warnings that Delta-T Alert™ provides allow for maintenance technicians to be warned of potential issues causing the elevated internal ambient temperatures.

How to Create A Safe and Effective Electrical Maintenance Program 2019 Image

How to Create A Safe and Effective Electrical Maintenance Program 2019

Condition based maintenance programs are slowly replacing calendar based processes due to the cost and time investment associated with calendar based inspections and in certain locales, to comply with published electrical safety regulations.  A condition based maintenance strategy for electrical assets requires planning and should be based upon the criticality of each electrical component.  If the risk of asset failure causes painful downtime and hurts a company’s bottom line, then that asset is classified as critical to the operation of the company.  With new innovations, critical electrical assets can be routinely inspected under full load in a safe and guarded condition at any time.  By collecting and trending inspection data, the maintenance team can monitor the reliability of an asset and determine when a fix or replacement activity needs to be scheduled.  The goal is to find the fault and fix it before it totally fails.

How To Specify Maintenance Inspection Windows 2019 Image

How To Specify Maintenance Inspection Windows 2019

Creating a Specification Requirement document for maintenance inspection windows requires consideration be given to many elements such as:

+ field of view

+ the type of technologies available (infrared, infrared & ultrasound combo, partial discharge)

+ the size of windows needed to accurately inspect the targets

+ the shape of windows needed to accurately inspect the targets

+ the environment that these windows are located in

This webinar will focus on key critical elements to be considered for specifying the appropriate maintenance inspection window to meet your needs.

The Theory and Effects of Partial Discharge 2019 Image

The Theory and Effects of Partial Discharge 2019

Partial discharge is an electrical discharge that does not completely bridge the space between two conducting electrodes.  Partial discharge can be the first observable indication of problem at a junction and if not corrected, will continue to worsen and potentially cause a catastrophic failure of equipment.  This webinar explains what partial discharge is, where partial discharge may occur and how to use infrared, ultrasound for visual inspections to find evidence that partial discharge is occurring.

What is Spot Vs. Area Temperature Measurements as part of an Electrical Maintenance Inspection?

In today’s business world, it is mission critical that a company introduce programs and procedures that will identify faults or deviations in critical electrical assets before the asset fails.  Electrical asset failures can lead to lengthy unscheduled downtime and potential loss of revenue for the company, not to mention costly repairs. Is it possible to identify an asset that is deteriorating and arrange to fix it before it fails? YES, it’s called Condition Based Maintenance.

Electrical equipment requires periodic maintenance to maintain normal operations. These inspections must often be performed on the assets operating under full load conditions. The inspections require direct access or direct line of sight to the energized components inside the electrical system. Traditionally, these inspections were time-intensive and required access panels and doors to be opened which can be extremely dangerous to the personnel performing the inspection task. The inherent safety risk as well as time and cost requirements needed to perform these inspections often led management to push out or cancel a maintenance inspection schedule which could lead to catastrophic asset failures causing downtime and, sometimes severe injury or loss of life.

Innovative technologies called Electrical Maintenance Safety Devices [EMSDs] have emerged that improve the efficiency of electrical inspections. EMSDs maintain an energized compartment’s closed and guarded condition during the inspection process thereby reducing the time needed to complete the inspection and ensuring that the inspectors are not put at risk.

EMSDs exist to facilitate the most common inspection type – infrared thermography. Part of an electrical inspection may include temperature measurements using an infrared window and infrared camera. There are several measurement settings on the Infrared Camera that the thermographer can select: two settings are SPOT and AREA MAXIMUM.

                                                                                                         Spot Vs. Area Temperature Measurements

SPOT Temperature Measurements

A SPOT temperature measurement will show a temperature of a single point to which the camera is aimed. The problem with using the SPOT setting is it only measures the temperature of one single point. Unless the thermographer continuously moves and aims the camera around the entire area of the panel, he may not see a particular temperature that is suspect or outside of specification. A SPOT measurement is useful when trying to compare the temperature of one item to another or when trying to correlate one component to another.

AREA Temperature Measurements

When the infrared camera is set on the AREA MAXIMUM temperature measurement, it provides the maximum temperature across the entire area within the area square on the camera screen. This setting provides the thermographer with more information and more accurate temperature readings inside the entire panel. As a result, he is less likely to miss a hot spot 11 is recommended to select the AREA MAXIMUM temperature setting on the infrared camera when performing electrical inspections.

Thorough understanding of the difference between SPOT and AREA temperatures allows the thermographer to assess the health of energized electrical components safely and routinely.


EMSDs allow for more frequent inspections leading to the creation of asset health history files and the capability of performing data trend analysis on the assets. Temperature trending using infrared thermography is one type of electrical inspection that allows the maintenance team to monitor the health of energized electrical assets.


NFPA 70B Tip

NFPA 70B Tip

It has long been known that “dependability can be engineered and built into
equipment, but effective maintenance is required to keep it dependable”, but where do
we get the guidelines to ensure the maintenance programs we design are effective?