Ratio Pyrometer Technology

Ratio pyrometers are different from single-wavelength pyrometers in that 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 pyrometers to compensate for emissivity variation, partially filled fields of view and optical obstructions.

There are two types of ratio pyrometer technologies, and Williamson is the only company to offer both. Two-Color technology uses a sandwich detector and a fixed set of wavelengths. Dual-Wavelength technology uses a single detector with two unique and selectable wavelengths, which allows for all of the benefits of a Two-Color pyrometer plus some other significant added capabilities.

Reducing Errors

Ratio pyrometers help reduce total measurement error by automatically compensating for emissivity variation and misalignment.

With the appropriate wavelength selection, Dual-Wavelength pyrometers can eliminate interference from common industrial obstructions like steam, water, flames, combustion gases, plasma, and laser energy. Two-Color pyrometers, because of their fixed wavelength set, will still experience some error whenever these interferences are encountered.

Popular Ratio Pyrometer Applications

  • 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

Two-Color

  • General purpose wavelength set
  • Can tolerate modest misalignment and partial field of view
  • Compensate for variable emissivity and modest optical obstruction or misalignment
  • Used when there is a clear optical path between the pyrometer and target
  • Measure temperatures above 1100ºF / 600ºC
  • Ideal for scale-free and uniformly heated ferrous material

Two-Color pyrometers are ratio pyrometers that can compensate for emissivity and misalignment. However, TC 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. Anytime these interferences are encountered, the TC technology will read in error.

Common Applications

  • Forging
  • Steel Mills
  • Heat treating applications

Dual-Wavelength

  • Carefully selected wavelength set
  • Compensate for variable emissivity, temperature gradient, severe optical obstruction, and misalignment
  • Select wavelength sets tolerate water, steam, flames, combustion gases, plasma, and laser energy
  • Separated wavelengths produce a heavily weighted reading towards the hottest temperature viewed, broad temperature spans, and low-temperature ranges
  • Measure temperatures above 200ºF / 95ºC
  • Better tolerates scale, temperature gradients, and non-grey interference (20x smaller errors) due to greater separation between wavelengths.

Common Applications

  • 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