A simple but interesting history of Infrared Thermometers
--- All Rights Reserved ---
Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:
This notice is included in its entirety at the beginning.
There is no charge except to cover the costs of copying.
It is very difficult to prove the accuracy of the order of inventions, so we have adopted the file dates of patents for our chronology.
ZyTemp accepts no legal or academic responsibilities for the true first inventor.
1884, The beginning
Figure 1: LE Boltzmann(1844-1906)
Stefan-Boltzmann's Law of black body radiation:
In 1884, L.E. Boltzmann showed how Josef Stefan's empirical T4 Black Body Radiation Law, formulated in 1879, could be derived from the physical principles of thermodyamics.
Boltzmann's findings were elegant, yet simple:
Radiation Power = Temperature4 x Constant
Consequently, Boltzmann has been named as the father of infrared thermometry.
In infrared thermometers, a small CPU inside the device uses this formula to accurately predict the temperature of a target.
1892, The disappearing-filament optical pyrometer
The earliest infrared thermometer (IRT) was known as the disappearing-filament optical pyrometer.
The glowing brightness of a heated surface as a means for measuring temperature was first suggested by Becquerel in 1836, but it was not until 1892 that the French industrialist Le ChateLier introduced the first laboratory radiation thermometer.
1899, The first patent for disappearing-filament optical pyrometer:
The first patent for the optical pryometer was granted to Morse in 1899. Holborn and Kurlbaum, apparently unaware of the Morse patent, independently developed a similar disappearing-filament optical pyrometer in 1901.
Figure 2: Morse's patent : the disappearing-filament pyrometer (1899)
In Morse's improved apparatus some difficulties of previous optical pyrometer are overcome by so organizing the same as to permit a comparison based on the fact that if two substances are made to produce in the eye the same color effects or sensations and one of them, or a portion thereof is arranged in the path of the rays passing from the other to the eye the portion of the one so arranged or superposed will merge in the other and apparently be obliterated from view.
The Leeds&Northrup Company acquired the Morse's patent of 1899 and in 1917 produced a commercially available disappearing-filament optical pyrometer similar to the one developed by Holburn and Kurlbaum.
However, one of the main disadvantages of the disappearing-filament optical pyrometer (even till today) is its large size and need for an attendant for operation. They are still in use today because of their high degree of accuracy and useful functionality.
1913, If the Titanic were able to detect icebergs.....
We are reminded of how the Titanic sank after striking an iceberg, but is there a way that we can show such a disaster could have been avoided?
L. Bellingham presented a method to detect the presence of icebergs and steamships by using a mirror and the original thermopile. He later patented this device in 1913. His infrared thermometer's primary advantage over the disappearing-filament optical pyrometer was that it was able to detect temperatures substantially lower than ambient. If the Titanic crew had this device on hand, they would have been able to steer clear of their grave tragedy!
Figure 3: Bellingham's Infrared Thermometer(1913)
1931, Finally, a practical commercial product
In addition to their accomplishments in 1917, the Leeds&Northrup Company introduced the first commercially-available total radiation thermometer.
1968, Emissivity altered
The evolution of the IRT came about in various forms. One of these embodiments is described in the patent shown in Figure 4:
The file date is 1968 July, it's still an analog; heavy device, with bulky shutter (or chopper), require long time to stabilized. this device uses the pyroelectric crystal as detector.
Figure 4: Pyrometer employing a pyroelectric crystal detector
US3586439: DIRECT READING PYROMETER EMPLOYING PYROELECTRIC CRYSTAL DETECTOR
Country: United States of America
Inventor: Treharne, Richard W.; Xenia, OH
Assignee: Kettering Scientific Research, Inc.
Published / Filed: 1971-06-22 / 1968-07-15
1973, The development of the short range IRT
In 1973, a short range IRT was created by Sensors, Inc. It utilized a pointer to identify the exact location of measurement. Figure 5 shows the IRT:
Figure 5: Apparatus for IR radiation temperature measurement
Title: US3777568: D. C. ELECTRONIC APPARATUS FOR IR RADIATION TEMPERATURE MEASUREMENT
Inventor: Risgin, Ojars; Grass Lake, MI
Szeles, Donald M.; Ann Arbor, MI
Assignee: Sensors, Inc., Ann Arbor, MI
Published / Filed: 1973-12-11 / 1971-12-21
1977, Revolution of a sensor: the miniature thermopile
It has been known that evaporating overlapping films of antimony and bismuth could form thermocouples. Since this construction is more rugged than that of the traditional thermopile, it became advantageous that this method be applied for the construction of thermopiles. This would lead to a significant development of the thermopile for space applications because of its small critical mass.
Overlapping areas that form the junction (hot) are fashioned on a thermally insulating layer set, or cold junction, in the middle of an aluminum block, which served as a heat sink. A reference junction is formed where the evaporated films come in contact with the aluminum block. Since the junctions have a very low specific heat, the time constant of an evaporated thermopile can be as short as 10 milliseconds. Furthermore, this evaporation technique allows the thermopile to be easily conformed to any size or shape.
Figure 6 shows the first miniature radiation thermopile, its sensor is smaller than 4mm2.
The first miniature infrared sensor, before this invention, the infrared sensor is as large as a coin.
Now, it can be smaller than a bean (4mm).
Figure 6: Small high-performance radiation thermopile.
Title: US4111717: Small-size high-performance radiation thermopile
Inventor: Baxter, Ronald Dale; Furlong, PA
Assignee: Leeds & Northrup Company, North Wales, PA
Published / Filed: 1978-09-05 / 1977-06-29
1984, 6,000,000pcs of Infrared Thermometer for ear
In 1984, a major milestone occurred for infrared thermometers. IRT applications were soon found in the hospital, home, and ear! One of the turning point applications - the infrared ear thermometer - resulted in the sale of six million pieces, and consequently a substantial drop in the IRT's sensor cost.
This remarkable invention (USP4602642), has continued to evolve, and continues to thrive in the market today.
Figure 7a/b show the original patent and modern day product:
Figure 7ab: Original picture of patent
Figure 7b: Modern day picture
US4602642: Method and apparatus for measuring internal body temperature utilizing infrared emissions
Inventor: O'Hara, Gary J.; Escondido, CA ; Phillips, David B.; San Diego, CA
Assignee: Intelligent Medical Systems, Inc., Carlsbad, CA
Published / Filed: 1986-07-29 / 1984-10-23
2002, The Most compact Infrared Thermometer
In July 2002, ZyTemp introduced the world's smallest infrared thermometer (IRT), the TN105. The TN1 is as small as the battery of some of today's IRTs, and with it's anti-thermal shock capability, it can handily outperform traditional counterparts (You can put 2~4pcs into your shirt pocket.)
2003, Infrared meets Thermocouple
In July 2003, ZyTemp unveiled the TCT1, a low cost, high value infrared + thermocouple thermometer. In this design, non-contact and contact functionalities are conjoined to produce a dual utility of instant results (infrared) and high accuracy (thermocouple).
D.P.DeWitt "Theory and practice of radiation thermometer" P13-P15
 Richard D. HUDSON, JR "Infrared System Engineering" P272