How does Fluoroptic technology work?

Luxtron’s founder, Dr. Ken Wickersheim, invented and patented Fluoroptic thermometry in the 1970s. Ever since, Luxtron has been developing, improving, and optimizing the technology for temperature measurements across a broad variety of industries.

Fluoroptic technology takes advantage of optical properties inherent in phosphorescent (links to question below) materials. The instrument determines the temperature of the sensor by measuring the decay time of the emitted light. It is a persistent property of the sensor that its decay time varies precisely with temperature.

Fluoroptic technology uses a fiber optic to connect the sensor (a phosphor, similar to the phosphors used on TV screens) to the instrument. The instrument sends pulses of light down the fiber to the sensor. This light “excites” the phosphorescent sensor causing it to emit light at a different color (longer wavelength). The “emitted” light travels back into the fiber optic to the Luxtron instrument.

Because the excitation light and emitted light are different colors the instrument can distinguish between the two. Generally speaking, the colder the sensor the longer the decay time of the phosphor’s emitted light.

What are the key advantages of Fluoroptic technology?

Fluoroptic probes are simple to use, 100% non-metallic, robust, and can be made very small in size. They can be packaged in a variety of shapes and materials that are suitable for any environment.

• SAFE: Non-metallic means no short circuits, no sparks, and no conduction.
• IMMUNE: Electrically non-conductive probes are not affected by RF and EMI.
• ACCURATE: Because the sensor is not connected to the instrument with metal lead wires, the sensor does not perturb (act as a heat sink to) the object being measured. This is especially critical when accuracy is important or when the mass of the measured object is relatively small.
• NO RECALIBRATION: Because the sensor used by the probes is stable and does not degrade over time, no recalibration is necessary.
• FAST RESPONSE: The small size means small thermal mass.
• NON-CONTAMINATING: The sensor is chemically inert and does not react or corrode. In addition, most standard probes are encapsulated in PFA Teflon® giving them nearly universal chemical resistance.
• VERSATILE: The sensor material can be formed into various probe styles to meet the needs of specific application circumstances.

What temperature range can be measured?

Standard instruments and probes offered by Luxtron measure from -100°C to +300°C. The technology is capable of measuring from -200 to over 1000°C. However, extending this temperature range requires special probe materials that can survive the higher temperatures.

Where are Fluoroptic probes used?

Fluoroptic probes are used across a vast number of fields and have become the standard of choice for critical medical, semiconductor and electric power applications. Example applications include:

• High voltage equipment monitoring,
• Inductive heating control,
• Closed-loop control of medical therapies using RF and/or microwave,
• Testing medical implant compatibility with MRI,
• Microwave food development,
• Semiconductor processing,
• Safe measurements of flammable or explosive materials,
• Operational testing of live electrical circuits.

What is a phosphor? And what is phosphorescence?

Phosphor refers to a chemical substance that exhibits fluorescence when excited by light, ultraviolet radiation, x-rays or an electron beam. The amount of visible light that fluoresces is proportional to the amount of excitation energy. If the fluorescence decays slowly after the excitation source is removed (or turned off), then the substance is said to be phosphorescent.

Phosphorescence is the result of electron singlets moving between molecular orbitals. The excitation radiation moves an electron singlet up to an excited orbital state. However, this position is quantum mechanically quasi-stable and the electron will eventually relax to its ground state. This thermodynamically induced movement (to a lower energy level) dissipates the energy difference in the form of a photon, or light.

Because the movement of the electrons is necessarily a kinetic and thermodynamic process, phosphorescence is by definition a temperature-dependent process. It is this intrinsic property of phosphorescence that Luxtron’s Fluoroptic probes take advantage of to measure temperature.

Chemically, phosphors are transition metal rare earth compounds of various types. The element phosphorus is NOT a phosphor. See below for details.

Do Luxtron probes contain any phosphorus?

No, Luxtron’s sensors contain none of the element phosphorus. The sensor is a “phosphor” which is different from the element phosphorus. The German alchemist, Hennig Brand, discovered the element phosphorus in 1669. While Brand did not discover the gold he was looking for, his discovery of phosphorus was the first element to be isolated beyond those already known since antiquity, such as gold, copper, lead, sulfur, etc. It was the 13th element to be isolated and it led to the invention of the match (a very worthwhile development indeed).

But, the initial excitement provided by phosphorus was its ability to glow in the dark. The name comes from the Greek word phosphoros meaning “light bearer”. Hence, since the discovery of Phosphorus, the term phosphorescent has been used to describe any substance that gives off light without burning (see further details above). Thereby, a phosphor is any material that exhibits the phenomenon of phosphorescence.

Oddly enough, the element phosphorus is not technically considered to be a phosphor. Phosphorus emits light (glows) in a reaction with oxygen. Phosphorus immediately combusts (burns) when exposed to oxygen and forms P4O10.

Why does phosphor make a good sensor?

The phosphors used by Luxtron offer excellent sensing properties. The phosphors are fabricated using solid-state reactions and are sintered at temperatures greater than 1200°C. This produces a stable and inert material whose properties cannot shift and therfore never requires recalibration or replacement. Key properties of our phospohor sensor that make it well suited for sensing:

• Long Term Stability,
• Repeatable and Uniform Quantum Properties,
• Chemically Inert, and
• No Hysteresis.

Fiber optics are a modern transmission technology of information by means of a light signal guided by a small diameter fiber. The fibers can be made of various materials that are capable of transmitted light; typically a high-grade glass but polymers can also be used. Luxtron uses high-grade all-silica fiber for most of our standard probes.

The light passes down the “core” of the fiber by means of “total internal reflection”. Only light that falls within the “numerical aperture” (shown as 2 in the figure below) of the fiber is accepted. Light outside this angle is not reflected internally down the fiber. The numerical aperture is a function of the relative refractive indices, n, of core and cladding materials. The figure below illustrates this phenomenon.