Ratio Pyrometer Technology

Ratio Pyrometer Technology

Product Description

Williamson is the only company that can offer two different ratio technologies: two-color and our unique dual-wavelength. Ratio pyrometers are different from single-wavelength pyrometers because they measure infrared energy at two wavelengths instead of one. The ratio of energy between the two measured wavelengths is then converted into a temperature value. This method of measurement allows ratio industrial infrared pyrometer technology to compensate for emissivity variation, partially filled fields of view, and optical obstructions.


Two-color pyrometers use what is called a “sandwich detector” using a fixed set of wavelengths, meaning that two wavelength filters are laid one on top of the other. One wavelength is a broad waveband (0.7-1.1um for example) and the other wavelength is a narrow waveband (1.0-1.1) that is a subset of the broader band.

  • General purpose wavelength set
  • Can tolerate modest optical obstructions, misalignment and partial field of view
  • Compensate for variable emissivity
  • Used when there is a clear optical path between the pyrometer and target
  • Can only measure temperatures above 1100°F / 600°C

Keep in mind that two-color pyrometers cannot view through common optical interferences, so it is critical to avoid water, steam, flames, combustion gasses, plasma and laser energy for the most accurate and repeatable results.


Dual-wavelength pyrometers use two separate and distinct wavelength sets on a filter wheel. Because the design allows for separate wavelengths, these wavelength sets can be independently selected and combined allowing for some unique capabilities.

  • Compensate for variable emissivity, temperature gradients, severe optical obstructions, and misalignment
  • Select wavelength sets tolerate water, steam, flames, combustion gasses, plasma, and laser energy
  • Separation of wavelengths produces a heavily weighted reading towards the hottest temperature viewed
  • Available in broad temperature spans and low-temperature ranges
  • Includes ESP filtering to continuously measure intermittent targets or eliminate intermittent interferences

Dual-wavelength pyrometers offer two different and selectable wavelengths allowing for all of the benefits of a two-color pyrometer plus some additional capabilities.


Ratio Pyrometer Comparison

Capabilities of Ratio Pyrometer Wavelength Sets


Ratio Technology Wavelength Set Characteristics
Two-Color (TC) 11 Avoid water, steam, large flames, combustion gasses, plasma, and laser energy
Dual-Wavelength (DW) MS Specialty dual-wavelength set used to measure molten steel/iron and small flames
08 Able to view through thin layers of water (< 5mm), steam, combustion gasses, small flames, and plasma
12 Broad temperature spans, but not appropriate for viewing through steam, large flames, or combustion gasses
24 Excellent at viewing through steam, laser energy, and plasma
28 Measures exceptionally low temperatures, down to 200°F / 95°C, cannot view through common interferences


Popular Applications with Ratio Pyrometers Include:

  • Steel Mills
  • Casting, Forming, Joining, and Heat Treating of Metals
  • Induction, Resistance, Friction, Flame, and Laser Heating
  • Forging Plants: Billet, Die, Heat Treat
  • Wire, Rod, and Bar Mills
  • Rotary Kilns, Thermal Reactors, and Solid Fuel Power Boilers
  • Engineered Materials: Silicon Crystals, CVD Diamonds, Carbon Densification, High-Temperature Ceramics

As an industry leader, JWII can deliver a great deal of relevant knowledge to customers seeking a wide variety of products and applications. We have the tools and people necessary to provide impactful solutions and, with a long track record of success, we pride ourselves on the ability to provide continuous support to a diverse customer base, spanning several continents and markets.

  • Installation
  • Maintenance
  • Repair and Modifications
  • Modification of existing installations
  • Emergency Repair
  • Commissioning
  • Site Services
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