Frequently asked questions
regarding IR thermography and Infrared Windows
1. Can you survey electrical
equipment by just looking at the enclosure temperatures
with an infrared camera?
2. What are the minimum dialectric
clearances?
3. What is the effect of using infrared
windows on certified enclosures?
4. What effect do the windows have
on the thermal image?
5. Do we have to have a crystal or
can we use a grill?
6. Can we have one lens and use it
in all of our windows as we go?
7. Are custom materials or sizes
available?
8. Who can install and service an
IR window?
9. How long is the warranty on your
IR windows?
10. What materials do you use in
the construction of your IR windows?
11. What does IP65 and IP2X mean?
12. Can we install IR windows in
the field?
13. What is the Arc Flash rating
of your IR windows?
14. What are the benefits of fitting
IR windows?
15. Why do I need bigger Infrared
windows?
16. How Can I measure the transmission
rate of an infrared window?
Q.
Can you survey electrical equipment by just looking at the
enclosure temperatures with an infrared camera?
A. You cannot obtain adequate or reliable
information with an infrared camera without looking at the
actual electrical components. The majority of thermographic
cameras are based on digital camera technology and therefore
requires a direct-line-of-site to record an accurate image.
Surveys are hampered by cabinet designs that obscure the
target components being imaged and thermographers are put
at risk by having to open cabinets or doors in an attempt
to gain access to the internal components that they wish
to image, even the most comprehensive risk assessments and
method statements cannot avoid the obvious risks involved.
The use of Infrared Inspection ports is becoming more common
place, in fact electrical panel manufacturers are now fitting
Infrared inspection ports, grills, mesh screens, etc. in
an attempt to make their panels infrared friendly.
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Q. What are the minimum
dialectric clearances?
A. -The most important area of concern
is the maximum safe distance between the IR window and any
live components; this is called the “dielectric clearance”.
The recommended minimum dielectric clearances are as follows:
5 Kv Equipment -no less than 4 inches !!
15 Kv Equipment -no less than 6 inches !!
It must be noted that under no circumstances can the minimum
clearances be compromised.
Another important point to remember is that
most IR cameras can not focus closer that 4".
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Q. What is the effect of
using infrared windows on certified enclosures?
A. If the panel that you intend to
fit the IR window into carries any certification marks then
these should where reasonably practicable not be breached
in any way. In the case of a panel with UL certification,
you should only consider using UL recognized components;
a question that is regularly asked is how does field installation
of IR windows affect the UL status of the panel?
The component (in this case, IR window) can be field or
factory installed. The issue is the listing of the product
in the field to which it is installed. Installing this product
in the field does not negate the listing mark. Customers
often modify assemblies that are UL listed and marked. Any
modification done in the field is not covered by an existing
UL mark. Therefore, UL is not responsible for the certification
of these listings.
When changes are made to listed assemblies that affect the
rating of the equipment, UL will do a field inspection of
the modified product to re-certify the equipment meets UL
requirements. A customer may request this to be done. The
IR window would have to be added to the UL procedure for
that piece of equipment. If it is not covered in the UL
procedure then UL could not re-certify.
In cases where the IR window is not part of a product’s
UL listing, there is another option, the field evaluation
by UL. Since the IR window is a UL recognized component,
UL should be able to provide a UL mark that would verify
the modified product had been evaluated. However this would
probably not be required in most cases.
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Q. What effect do the windows
have on the thermal image?
A. The lens material's ability to absorb
some of the infrared radiation will lower the perceived
temperatures somewhat. This can be accounted for with a
simple procedure or by adjusting the transmissivity setting
on your camera or software. The clarity of the image will
not be affected.
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Q. Do we have to have a
crystal or can we use a grill?
A. Where there is no risk to the operator
of electric shock or flash over, a viewing port with no
crystal but with an inner protective grill may be installed
to protect the assembly from objects falling into the component
during inspection but still allow full access for an image
to be taken.
However you must ensure that all grills have
a maximum diameter of 12mm (IP2X) and you should also be
aware that the use of grills still requires the use of full
personal protective equipment as they are not compliant
with NFPA 70E as the thermographer is still exposed to energised
components within the panel being inspected.
NFPA 70E
IP2X
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Q. Can we have one lens
and use it in all of our windows as we go?
A. Where there is no immediate risk
to the operator of electric shock, he or she may use a view
port with a removable crystal option, resulting in significant
savings as only one crystal will be required regardless
of how many viewing ports they may have. This also allows
you to use viewing crystals such as coated ZnSe which has
a 99% transmission rate from 4-14 microns. ZnSe is too expensive
to use in large quantities, but because you only require
one crystal with the IRISS you can take advantage of the
best IR viewing crystals on the market, together with the
additional benefits that using them brings, at a fraction
of the cost. The VPLC-50 lens carrier includes a lens and
lens housing. This assembly fits into the VPR-50 windows.
Both a VPLC-50 lens and VPR-50 windows are required to use
the removable lens system.
However once again the use of a removable
lens system is not NFPA 70E or IP2x compliant, and should
you decide to use this system full precautions must be taken
regarding the correct level of personal protective equipment.
NFPA 70E
IP2X
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Q. Are custom materials or sizes available?
A. Custom window sizes, design, and
materials are available, however the prices will vary depending
on the material, specifications, and possible the number
of units ordered. You must be aware that when adopting this
approach the IR window is not tested or certified to any
recognized standard and local approval must be gained to
certify their use.
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Q. Who can install and
service an IR window?
A. The IR window must be installed
and serviced only by qualified electrical personnel, more
information regarding installation can be found in this
website.
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Q. How long is the warranty
on your IR windows.
A. Our general purpose IR windows using
the IR polymer are guaranteed for the life of the panel
in which they are fitted, they are not guaranteed against
damage or mis-use. As our IR windows do not use any adhesives
in manufacture or installation our products can be moved
or upgraded with ease, We do not however give a warranty
on any of the Fluoride crystals as they are hygroscopic
and fragile, therefore they will fail eventually.
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Q. What materials do you
use in the construction of your IR windows?
A. The Bodies and gaskets of our IR
windows are constructed from flame retardant plastics and
rubbers, with regards to the lens materials a full list
can be found in our Materials pages on this website.
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Q. What does IP65 and
IP2X mean?
A. IP65 and IP2X are integrity proofing test
against agreed standards. IP65 relates to a NEMA 4 classification,
a copy of the full report can be downloaded from this website.
SIRA IP Test Report
NEMA Standards
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Q. Can I install IR windows
into our field installations?
A. There are many issues to be considered
when it comes to the field installation of IR windows. The
first point of call should be to the manufacturers of the
equipment to discuss any associated risks and produce a
risk assessment and method statement covering all the requirements
of the installation, you should then contact any relevant
certification bodies regarding the install procedure, fitting
instructions and certifications of our IR windows. Remember
that under no circumstances can you impair the integrity
of the panel in which you intend installing IR widows.
In the case of UL I have attached a copy of
a letter that we received from them outlining that during
the testing of our IR windows that consideration was given
to their suitability for field installation when installed
following our installation instructions.
UL Letter re: Field Installation
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Q. What is the Arc Flash
rating of your IR window?
A. No IR window or individual component
can ever be Arc Rated or can protect you from Arc Flash,
Arc flash has the potential to produce a shock blast of
up to 700 miles per hour with a core temperature of 15,000
C, and there are no materials that can resist that type
of temperature and force (See Video). Panel assemblies are
designed to contain and survive differing levels of arc
flash energy.
There are industry standards designed to test panels for
resistance to Arc Flash. If these assemblies are tested
with IR viewing ports fitted, and pass the test, the standard
is awarded to the assembly only, this does not mean that
the IR window or any other components are Arc rated for
any other assembly.
Each assembly needs to be dealt with in a
case by case scenario and comprehensive risk assessments
completed.
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Q. What are the benefits
of fitting IR windows?
A. To a thermographer there are many
benefits to using IR windows, direct temperature readings
will always be the preferred medium for gathering information
especially on critical plant and services. IR windows are
an asset to any inspection program and remove the necessity
of:
Complex risk assessments and method statements
prior to an “open panel” inspection.
Opening panels and exposing manpower to potentially hazardous
live components.
Permits to isolate and shutdown panels.
Restarting plant after shutdown.
The additional benefits of using of IR windows are:
Improved thermographic survey results, as
they are direct temperature measurements.
Improved plant reliability.
Safer working environment for thermographers.
Reduces the amount of time and costs involved in a thermographic
survey, as no shutdowns are required. .
IR windows make our work safer, faster and more accurate,
but only when installed and used correctly. If careful consideration
is not given to the issues discussed in this paper the inspection
port will give inaccurate results leading to poor diagnosis,
thus negating the reason for fitting them in the first place.
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Q.Why do I need bigger
Infrared windows?
A. We have produced a paper outlining
all the factors that need to be considered regarding this
very subject.
Why do I need bigger IR windows
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Q. How Can I measure the
transmission rate of an infrared window?
A. It must be noted that specialised
instrumentation is used to measure the spectral transmittance
of IR window materials, however as the majority of thermographers
are unable to access this type of instrumentation we have
to derive methods of using our IR cameras to calculate the
approximate transmission rates. I have used this method
in the field many times and it has proven to be accurate
and reliable, we call it the “coffee cup test”
Method 1: IR camera with external optics transmission
compensation:
1. Using electrical tape mark a low emissivity
target onto a coffee cup and fill the cup with hot coffee.
2. Set the transmission rate to 0.99 and the emissivity
to 0.95.
3. Measure the temperature of the emissivity target on the
coffee cup.
4. Place window in front of target.
5. Calculate the IR window transmission by adjusting the
camera transmission rate until the temperature reads the
same as the temperature without the IR window.
6. Mark transmission rates on IR windows.
Method 2: IR camera does not have external
optics transmittance compensation.
1. Using electrical tape mark a low emissivity
target onto a coffee cup and fill the cup with hot coffee.
2. Set IR camera emissivity to 1.
3. Measure target apparent temperature without window in
place.
4. Place window in front of target.
5. Adjust target emissivity until same apparent target temperature
without window is found.
6. When using IR windows in this mode, enter the product
of the target emissivity times the window transmittance
for emissivity in your IR camera.
7. Mark the calculated emissivity setting on the IR window
labels and ensure that all personnel using this calculation
fully understand the procedure used.
8. The major caveat here is that the target reflected apparent
temperature, the window reflected apparent temperature,
and the window temperature must all be equal.
Note:
This is a very popular method in use in the field today,
particularly as the majority of IR cameras do not have the
ability to adjust the optics transmission onboard the actual
camera, but do however allow you to adjust the emissivity
to obtain fairly accurate results using this methodology.
Method 3: Using IR camera reporting software:
1. Using electrical tape mark a low emissivity
target onto a coffee cup and fill the cup with hot coffee.
2. Set the transmission rate to 0.99 and the emissivity
to 0.95.
3. Take an image of the coffee cup measuring the temperature
at the emissivity target.
4. Place window in front of target.
5. Take an image of the coffee cup through the IR window
measuring the temperature at the emissivity target.
6. Save both images into your reporting software
7. Calculate the IR window transmission by adjusting the
transmission rate within the reporting software on the image
taken through the IR window until the temperatures read
the same as the image without the IR window.
8. Mark transmission rates on IR windows.
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