Wavelength Matters

Compensating for Optical Obstructions and Emissivity Variation with Single-Wavelength Sensors

Posted by Jonathan Stronach on Wed, Jan 18, 2017 @ 08:42 AM


Williamson Short-Wavelength Advantage

Infrared pyrometers rely on making a reading based on the amount of energy collected. The amount of energy collected can be affected by emissivity variance and optical obstructions. Selecting the shortest possible wavelength helps to eliminate variables such as emissivity variation and optical obstruction. Being less sensitive to these variables ensures for a more accurate reading compared to a general purpose long-wavelength sensor.

Emissivity Variance

Every object emits infrared energy proportional to its temperature. Infrared pyrometers collect the infrared energy emitted by an object and convert it into a temperature value. Emissivity is the percent of energy emitted by an object compared to the theoretical amount of infrared energy emitted by a perfect emitter at the same temperature. The amount of energy emitted is a function of both temperature and emissivity.


Therefore, the emissivity of a measured target has a direct correlation to the energy reading of a pyrometer. Emissivity varies due to changes in material, surface texture, degree of oxidation, micro structure or surface contamination. The emissivity of a material can also vary at different wavelengths. The graph to the right shows that selecting the shortest possible wavelength will result in smaller errors due to emissivity variance. In fact, short-wavelength sensors can be 4-20 times less sensitive to emissivity variation compared to long-wavelength sensors. By reducing the errors caused by emissivity variation short wavelength sensors produce a more accurate and repeatable reading.

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3 Infrared Technologies to Use in the World of Competitive Annealing

Posted by Kam Olaogun on Thu, Aug 18, 2016 @ 11:30 AM

3 Infrared Technologies to Use in the World of Competitive Annealing

Not all annealing lines have the same accuracy requirements. Some alloys require tighter temperature control than others. Plants that run high-strength steel or dual/complex-phase steel require precise control of steel temperature. Plants that run low-alloy steels for non-transportation and non-appliance applications often can produce a high-quality product with looser control of the steel temperature; however, these plants also benefit from the improved speed and energy efficiency associated with precise control of steel temperature. Regardless of alloy, effective temperature control of steel dictates the use of an accurate infrared pyrometer. Better temperature control allows plants to perfect their recipes which improves efficiency and lowers operating costs. Moreover, precise temperature control ensures final product quality and repeatability. Infrared pyrometers are the best solution for continuous annealing lines because of their ability to make accurate non-contact temperature measurements. However not all pyrometers offer the same level of performance and different wavelength technologies further validates this.    


Pyrometers are typically installed on a continuous annealing furnace using one of two mounting techniques.

1.) Roller Wedge

Roller_wedge.jpgThe roller wedge measurement technique, also known as the nip measurement technique or as the low-angle multi-reflective measurement technique, relies on the unique geometry associated with the roller nip combined with a low-angle of alignment to artificially enhance the apparent emissivity of the strip and to eliminate the influence of hot background reflections. Roller wedge measurement conditions are valid and the technique is appropriate only when certain conditions are met: (1) the roll and the strip are the same temperature and (2) the pyrometer must be mounted at the sweet spot—an appropriate shallow angle to produce a significant number of reflections.(*)


2.) Direct View

The direct view measurement technique is used when the roller wedge measurement technique is not

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Topics: wavelength, pyrometer, steel, annealing, wedge, temperature control

Billet Temperature Measurement: Typical Practices vs. Best Practices

Posted by Jonathan Stronach on Mon, Aug 8, 2016 @ 10:30 AM

Billet Temperature Measurement: Typical Practices vs. Best Practices

For the forging and extrusion industries there are two temperature measurements that should be made. The first is the temperature of the billet as it is being heated – to make sure that the heating system heats it to the correct temperature value, and the second is the confirmation of the billet temperature just before it enters the forging or extrusion press. In practice, most plants use only one pyrometer to make both temperature readings, but in reality these are two different measurements.

 Why Billet Temperature Matters

Billet Heating: Most plants measure the billet temperature after it exits the billet furnace. However, the temperature of each billet varies making this measurement too late for real time, precise feedback control. In order to actually control the temperature of each billet during the heating process, it is necessary to measure the billet while it is still inside the furnace. This technique is the only way to bblog.jpgcontrol the temperature of each billet to reach the exact process temperature.

Billet Confirmation: Process upsets and delays can result in a billet sitting and waiting before being loaded into the forging or extrusion press. If the delay is long and variable then the billet temperature can be low and variable. The lower temperature caused by the billet sitting can result in poor quality, excessive wear, process upsets, and in some cases damaged equipment.  

Typical Practice

The typical practice is to measure the billet temperature immediately after it exits the furnace. However, the corners of the billet typically heat faster and hotter than the bulk metal temperature. These hot corners can introduce a variable offset in pyrometer readings. But, if the temperature reading is taken 20-30 seconds after the billet exits the furnace, the corners have enough time to cool and the interference is eliminated. This typical practice for billet measurement is too late for feedback control and too early for billet confirmation. Moreover, the point of measurement coincides with the period at which the billet surface temperature is least uniform and most variable.

Best Practices

Billet Heating: Measure the billet while it is still inside the furnace. For the induction
heating process, the best configuration is a fiber-optic pyrometer that can view between the coil windings away from the end of the billet.

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Topics: pyrometer, aluminum, steel, Forging

EPA Flare Requirements: How Your Pilot Monitoring Device Stacks Up

Posted by Jonathan Stronach on Tue, Feb 2, 2016 @ 03:03 PM


 EPA Flare Requirements: How Your Pilot Monitoring Device Stacks Up

A dependable maintenance free pilot monitor is an important system component. If the flame pilot is out, hazardous gasses may be vented accidentally into the environment. Continuous operation of the flare stack is a critical EPA requirement for the proper operation of the system in order to prevent a major safety hazard. The EPA requirement 63.987 states: (c) “Where a flare is used, the following monitoring equipment is required: a device (including but not limited to a thermocouple, ultra-violet beam sensor, or infrared sensor) capable of continuously detecting that at least one pilot flame or the flare flame is present.” A complete description of requirements can be found on the official EPA website.

Flare Stack Where, How, and Why?   

Where?    Flare stacks or gas flares are large diameter, tall vertical vent pipes used for burning off flammable gas released by pressure safety relief valves. This occurs during unplanned over-pressuring of plant equipment. Flares are found in oil refineries, natural gas processing plants, petrochemical plants, steel mills, and landfills.

How?     The released gases and liquids are routed through large piping systems called flare headers to a flare stack. The released gases are burned as they exit the flare stacks. In order to keep the flare system functional, a small amount of gas is continuously burned, like a pilot light, so that the system is always ready for its primary purpose as an over-pressure safety system. Flammable vent gasses are ignited by a pilot flame when released into the atmosphere by petrochemical plants vessels or pipes.

Why? The proper incineration of these gasses is a critical safety and environmental concern. Therefore it is essential to confirm that the pilot is lit at all times. In industrial plants the main purpose of a flare stack is that of safety by protecting pressure vessels or pipes from over-pressuring due to unplanned operational upsets.

       Information in this section provided by: Encyclopedia of Earth                                          
                                                                                                              Pilot Monitor Technologies

Thermocouples    Currently many pilot flames are monitored using thermocouples that must be mounted at the flame. This system though effective, proves to be cumbersome when a thermocouple failure occurs.

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Topics: Petrochemical

Common Industrial Temperature Measurement Devices

Posted by Kam Olaogun on Tue, Feb 2, 2016 @ 03:02 PM

When it comes to taking a temperature reading for industrial applications there are a number of available options. Some of the more common instruments used are pyrometers, thermocouples, and resistance thermometers (RTDs). We are going to take a look at a general overview of these three temperature measurement devices and some of the key advantages/disadvantages of each.


Resistance Temperature Detectors or RTDs are contact sensors that operate under the principal that the resistance of a metal changes directly with temperature.  RTDs use pure elements like platinum for which the resistance has been well documented by a multitude of international standards institutes. The metal has a predictable change in resistance as the temperature varies; it is this change that is used to determine temperature. Here is more information on RTDs.



Thermocouples are also contact temperature measuring devices, consisting of two different metals joined together at one end. When the junction of the two metals is cooled or heated a voltage is produced that can be correlated back to a temperature. There are a number of different types of thermocouples, more information on the various types can be found here.

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Topics: pyrometer

The 3 Essential Forging Temperatures

Posted by Thomas Huff on Mon, Apr 6, 2015 @ 02:01 PM

The forging industry has a broad range of manufacturing processes, making many different types of products. From aerospace fasteners and the automotive industry, to hardware and tools, forged products can be found just about everywhere you look. The Forging Industry Association provides a great brief overview video of all the different types of forging processes. Aluminum, copper, steel and titanium are the most popular metals that are used in the forging process.  While there are a number of different ways to forge metal, the process essentially remains the same.  It requires heating a piece of metal and then deforming that metal into a particular shape. For some forged parts, temperature control is critical in achieving the desired metallurgical and structural properties of the newly forged part.  Here are three essential temperatures that need to be measured in the forging process.

1. Billet Temperature

There are really two types of billet temperature, one that is done inside a billet furnace (done for batch heating), the other is done prior to die entry to make sure that the part is hot enough before it enters the die.

1a. In-Furnace Measurement


In a forging plant, aluminum, brass, or steel billets are heated in furnaces before they are loaded into the forging die to be formed.  Billets may be large or small and the billet furnace may be gas-fired or induction-heated.  In some cases only the end of a product, such as the end of a rod or tube, is heated and formed.  In other cases, the entire billet is heated.  The efficiency of the heating process and the consistency of the formed product rely on a well-controlled billet preheat temperature.

When measuring inside a gas-fired furnace wavelength selection is critical to sensor performance. Infrared temperature sensors need to be filtered at wavelengths that view through flames and combustion byproducts without interference in order to make an accurate reading. Ratio pyrometers are typically recommended as they automatically compensate for emissivity variation and can tolerate moderate surface scale. If you have a wide tolerance for temperature error, single-wavelength pyrometers filtered at a short-wavelength can be used to minimize sensitivity to emissivity variation and scale.

1b. Die Entry Measurement

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Topics: aluminum, steel, Forging

What Does It Mean to Be 'Accurate'?

Posted by Thomas Huff on Thu, Mar 26, 2015 @ 10:22 AM

It seems like every pyrometer manufacturer claims to be "accurate" and with each new model that is released, the big selling point is "improved accuracy" or "ensures accuracy." Well, I'm sure if you did a comparison test where you aimed different brands of pyrometers at the same material, you would get different temperature readings. So... how do you know which one is "accurate" and which one is reading in error? Unless you are working in a high-tech lab with sophisticated and calibrated reference equipment it would be difficult to tell.

Most pyrometers are calibrated against blackbody furnaces and when you aim any type of pyrometer (long-wavelength, short-wavelength, ratio, etc.) against a blackbody furnace, it will be accurate. Just about any pyrometer can make an accurate reading while aimed at a blackbody furnace under ideal laboratory conditions.  However, most industrial applications that use infrared pyrometers for process temperature control are far from ideal laboratory conditions.  The chart below depicts a number of difference sources of temperature error that could lead to less "accurate" measurements.



Out of the 5 sources of errors listed - only one is really in the control of the pyrometer manufacturer: Pyrometer Calibration. Again, this is making sure that when aimed at a blackbody furnace, the pyrometer reads correctly.  The other 4 factors are all dependent on the end user's process once the pyrometer is installed.  All of these factors can influence the reading and "accuracy" of the pyrometer.  However, with the right wavelength selection, and using the appropriate infrared technology, these sources or error can be reduced or even eliminated. I'll go through these one by one.

1. Optical Obstruction

This is probably the biggest application challenge for most non-contact temperature measurements: How do we deal with viewing through any number of these interferences (steam, flames, combustion gasses, water, etc.)?  The truth is that that depending on the wavelength of the pyrometer, you can actually view through these obstructions without interference.

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Topics: wavelength, pyrometer

New Pro Series Pyrometers Have Shipped!

Posted by Thomas Huff on Wed, Mar 18, 2015 @ 10:13 AM

It is a very exciting week here at Williamson as the first of our new Pro series pyrometers are finally out the door! The new Pro series design has undergone a housing makeover and is both smaller and lighter than our previous Pro series housing for a cleaner design.

  • New sensor interface board with a more user friendly design - makes it easier to adjust sensor settings.
  • Rear glass viewing hatch cover and a backlit display for easy to read menu parameters.
  • New electrical connector - better protection against electrical shock and EMI interference.
  • New Protective Cooling Jacket (PCJ) - provides protection against ambient temperature conditions up to 600°F/315°C.

Additionally, Williamson is proud to announce that we now offer a Two-Color ratio pyrometer in addition to our Dual-Wavelength ratio pyrometer. To learn more about the difference between the two ratio pyrometer technologies check out this blog post

For more information on the new Pro series pyrometers check out our datasheets and new product overview brochure. If you would like to receive helpful application notes and product updates delivered to your inbox click on the link below.

Sign Up for Product Update Emails


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Topics: pyrometer

The Difference Between Two-Color and Dual-Wavelength Pyrometers

Posted by Thomas Huff on Fri, Feb 20, 2015 @ 10:48 AM

In the world of infrared temperature sensors, there are two types of ratio pyrometers: Two-Color (TC) and Dual-Wavelength (DW).  Both use a ratio of energy measured at two wavelengths to create a temperature reading. This method of measurement allows ratio sensors to automatically compensate for emissivity variation (for 'greybody' materials), partially filled fields of view, and dirty windows. While both the Two-Color and Dual-Wavelength are ratio pyrometers, the design and the capabilities of each type of pyrometer are very different.

Two-Color pyrometers use what is called a "sandwich detector" meaning that two wavelength filters are laid one on top of the other.  One wavelength is a broad wave band (0.7-1.1um for example) and the other wavelength is a narrow wave band (1.0-1.1) that is a subset of the broader band.

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 to allow for some very unique capabilities.

The difference in design allows for two major technical benefits for the Dual-Wavelength pyrometer:

1) Because of the greater separation between wavelengths, Dual-Wavelength pyrometers are 20x less sensitive to scale and temperature gradients compared with Two-Color sensors.

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Topics: wavelength, pyrometer

The 6 Infrared Pyrometer Technologies

Posted by Thomas Huff on Tue, Feb 10, 2015 @ 09:23 AM

Pyrometers, or infrared temperature sensors, have been around for quite some time now and as you can imagine come in all different types and varieties. Many of them have different temperature spans, different optics, different designs, features, etc. There are thousands of different pyrometers available on the market today, so how do you tell the difference between them all.single_short99

Taking a step back and looking at the pyrometer market from a broader perspective, there really are only 6 different pyrometer technologies - each with their own unique characteristics and capabilities.  6 technologies are a lot easier to manage than making sense of the thousands of options available.

  1. Short-Wavelength Pyrometers
  2. Long-Wavelength Pyrometers
  3. Specialty-Wavelength Pyrometers
  4. Two-Color Pyrometers
  5. Dual-Wavelength Pyrometers
  6. Multi-Wavelength Pyrometers

 Below is a short description of each technology

1. Short-Wavelength Pyrometers

Short-Wavelength pyrometers can be defined as those that are short than 3um. Compared with Long-Wavelength pyrometers, errors are relatively small for moderate emissivity variation, optical obstruction and misalignment.

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Topics: wavelength, pyrometer