IRWeb INFO

Contents [FREE] - pp.127-128
Thermographic analysis of phacoemulsification based cataract surgery procedures
B.INNOCENTI, A.CORVI, R.MENCUCCI pp.129-140

Scale reduction in modeling landmine detection by IR thermography
A.MUSCIO, L.TAROZZI, M.CORTICELLI - pp.141-154

Improved ultrasound activated thermography using frequency analysis
A.GLEITER, C.SPIESSBERGER, G.BUSSE- pp.155-164

(more…)

{Image Courtesy Williamson Corporation}
From the Williamson IR website page on Applications of Dual Wavelength infrared thermometers:

“One of the greatest advantages of a dual-wavelength infrared thermometer is that the target can be smaller than the optical resolution of the sensor. This feature is particularly appropriate when viewing past an optical obstruction or when viewing a small or wandering target such as a thin wire…”

“For this application, the dual wavelength sensors are able to provide a relatively large target area of 0.5in diameter while measuring the significantly smaller wire. Using a dual-wavelength sensor it is possible to measure a wire that is less than 0.001in diameter and with a wander from side to side of as much as 0.2in.”

(ED NOTE: This IR thermometer type, dual wavelength or dual waveband wherein the dual signals are ratioed are sensitive to the ratio of the spectral emissivities in the two spectral wavelength bands and are only insensitive to emissivity changes if the emissivity ratio does not change.

In such a situation the object of measurement is called a gray body, and it is relatively rare except for some of the Iron Oxides that are found on Iron & Steel within the wavelength regions used by many commercial relatively “short wavelength”, infrared thermometers, eg: 0.7 to 2.5 micrometers.)

Concord,MA, USA — As seen on the Williamson IR website:

“Single wavelength infrared thermometers filtered in the short wavelength region of 2.0 to 2.5 microns offer good performance when measuring low emissivity materials at low temperatures.”

“The accuracy improvement associated with the shorter wavelength sensor is shown in the figure below. The shorter wavelength sensor shows an improvement in measurement from about 18°F (10°C) to about 5°F (2.8°C) when measuring a 220°F (104°C) target with a 10% variation in emissivity. This alone does not explain the total improvement in accuracy achieved by the component supplier. The short wavelength measurement also benefits from the fact that most metals have a higher emissivity value at the shorter wavelength. Therefore, considering these two benefits the shorter wavelength sensor offers as much as ten times more accurate readings than is a long wavelength sensor.”

{Image: Courtesy Williamson Corporation}

Read the rest of an actual case story at www.williamsonir.com/page.php/id/233

ED NOTE: The terms “Short Wavelength” , “low emissivity” and “low temperature” are relative, of course and here they are used in the context of a measurement in the 150 to 1000°F temperature region of unoxidized metal surfaces.

Radiation Thermometry: Fundamentals and Applications in the Petrochemical Industry (SPIE Press Book) by Peter Saunders.

This book was just released on 3 August 2007 It is available from the SPIE Press, ISBN: 9780819467836, price for SPIE Members: $39.00(USD), and Non-member: $47.00 (USD).

(I just got my copy last week!)

At last, someone has done a very thorough job on pulling together all the different details involved in solving this most difficult and long-standing measurement problem and written a exceptional book about it.

In it, both the Near IR and Mid IR measurement approaches are described in detail and the problems of other verification means are described. It is also an excellent review in MHO of the subject of Thermal Radiation (IR) Thermometry.

The author is an objective worker in the field, Dr. Peter Saunders, a well-known physicist who works at The Measurement Standards Laboratory (MSL), New Zealand’s National Metrology Institute.

His book, is the latest, but possibly not the last word, on this measurement problem area. But, after skimming through the chapters, I think it will be a while before anyone digs as deeply into this application area of temperature measurement as he has.

The problem was recognised by many organizations in the Oil Industry and just over 20 years ago another unique instrument was developed and patented by Exxon Research to help solve it and get around the limitations of the then workhorse instrument, the Disappearing Filament Optical Pyrometer.

That instrument concept in the form of several different models are manufactured by the Pyrometer Instrument Company under license from Exxon. Called The PyroLaser, it is used effectively to correct for emissivity in many uses and attempts to solve the measurement problem of reflected radiation in Petrochemical furnaces.

The Quantum I Portable Laser IR Thermometer, now made by Mikron Infrared, is a similar device and was designed by the original inventor of the patented Exxon Research device.

A competing Land Instruments device, the portable Cyclops 390B Furnace Pro uses a different approach by using an optimum measuring waveband, where estimated emissivity errors can be more readily tolerated.

I highly recommend a good read of Dr. Saunder’s book before one commits to buy anything. The price of it is negligible compared to any of the measurement devices on the market and and the savings of time it offers by his shared experience and theoretical knowledge.

Peter Saunders is a true expert and has done a very thorough and remarkable job that goes back over a period of several years.

My final comment is: I only wish I had the know-how, experience and writing ability to have written such a unique and well-done monograph. Kudos to Dr. Peter Saunders!

Ray Peacock

Temperatures.com