Pyrometer Spectral Range

When selecting an infrared pyrometer for a specific application, the spectral range of the pyrometer is one of the most important parameters to consider.  The spectral range defines the wavelengths that the pyrometer responds to.

Background

Non-contact temperature measurement involves the pyrometer measuring the temperature of a particular material based on the infrared radiation (IR) emitted by the material. A pyrometer's spectral range is a very small portion within the infrared region of the electromagnetic spectrum with wavelengths longer than those of visible light and shorter than radio waves.

All materials emit infrared radiation (IR), but they do not emit radiation uniformly over all wavelengths. Choosing a specific spectral range optimizes the pyrometer to respond to wavelengths suited to the material and/or how the pyrometer is applied.

Common Spectral Ranges

Although the usable portion of the infrared spectrum lies between the wavelengths of approximately 0.7 to 39 μm (and sometimes as low as 0.55 μm), the majority of pyrometers in the marketplace are offered with spectral ranges between approximately 0.8 to 14 μm (μm=microns).  A few examples of the commonly available spectral ranges are the following:
 

• 0.8 to 1.1 μm, commonly referred to as a "1 micron pyrometer"
• Narrow band 1.5 μm or 1.6 μm , which typically has a bandwidth of approximately 0.2 μm
• The wideband 8 to 14 μm spectral range

The importance of spectral range to non-contact temperature measurement applications is what led HEITRONICS to publish the spectral response curves of the standard spectral ranges offered within the pyrometer's users manual.  The spectral response curve of a spectral range defines the relative responsiveness of the pyrometer (or thermal imaging camera) over its full range of wavelengths.

An example of a HEITRONICS Spectral Response Curve is shown below; this one is for the 8 ... 14 micron Spectral Range:

The following is an example of the HEITRONICS Spectral Response Curve for the 5 micron Spectral Range:

HEITRONICS Models

Model numbers of HEITRONICS pyrometers are typically created to denote the spectral range of the model.  In the model number, the first four characters represent the pyrometer series (for example, the KT15 and CT18). The two numbers after the decimal point denote the spectral range.  For example, the model "KT19.82" is one of HEITRONICS KT19 series of pyrometers that has a spectral range of 8 … 14 μm.

Additional Examples of HEITRONICS models:

CT18.03 = 1 μm

CT18.04 = 1.6 μm

KT15.42 = 4.9 … 5.5 μm

Low, Medium and High Temperature Measurement Applications

The physics of making a non-contact temperature measurement by collecting the emitted infrared radiation from a target reveals a relationship between the spectral range and the temperature being measured.   Typically, higher temperatures are measured using shorter wavelength instruments, and lower temperatures are measured using longer wavelengths.

There are a variety of cases where the optimal solution for measuring temperature will not follow this low/medium/high temperature classification.  For example, high temperature ceramics are best measured with long wavelength pyrometers due to the typical infrared (IR) transmission characteristics of ceramics at mid and short IR wavelengths.  A common goal for selecting the most appropriate spectral range is to avoid wavelengths that transmit through the target.  Minimizing reflectivity and thus maximizing the effective emissivity is the goal (Emissivity + Reflectivity + Tranmissivity = 1.0).

Our definition of low, medium and high temperature intervals is generally estimated as the following:
 

• Low temperature applications can be between -100 … 500 ⁰C
• Medium temperature applications can be between 200 … 1000 ⁰C
• High temperature applications lie between 500 … 3000 ⁰C

For more on wavelengths and spectral ranges go here.

Please contact us for assistance on spectral range selection, or complete the Customer Application Requirements Form and send it to win@wintron.com for review by one of our experts.

Pyrometer Selection Guide

Low Temperature Measurement via Long-Wavelength Spectral Ranges

HEITRONICS infrared pyrometers are used for a wide variety of low temperature measurement applications, and support measurement requirements that range from general-purpose to specific and demanding. These low-temperature infrared pyrometers measure the temperature of diverse materials such as paper, thick plastics, rubber, textiles, asphalt, wood, construction materials, agriculture, food, sea/water surface, snow, ice, land, clouds/sky, painted metals, heavily oxidized steel, and low temperature glass.

Lower limits of measurement for the HEITRONICS low temperature pyrometer models include:  -100, -50, -30 or 0 ^oC

The measuring ranges of these models include the following: 

• -100 … 200 °C
• -50 … 200 °C
• -50 … 1000 °C
• -30 … 500 °C
• 0 … 3000 °C

Medium Temperature Measurement Via Mid-to-Longwavelength Spectral Ranges

HEITRONICS Mid-to-Longwavelength spectral range pyrometers measure the temperature of medium temperature measurement applications, which include temperature measurement of metals, refractory bricks, carbon/graphite, or viewing through hot combustion gases & flame, along with many other applications.

Lower limits of measurement for the HEITRONICS medium temperature pyrometer models include: 100, 140, 250 or 300 °C

The measurement range of these pyrometers include the following:
 

• 100 … 1400 °C
• 140 … 1000 °C
• 250 … 1400 °C
• 300 … 1500 °C

High Temperature Measurement Via Short Wavelength Spectral Ranges

HEITRONICS short wavelength spectral range pyrometers measure the temperature for high temperature measurement applications.

Depending on the pyrometer model, the lower limit of measurement can be 200 °C with an upper limit of 3,000 °C. The CT18.04 model can be made with two temperature ranges to cover 200 °C to 2900 °C in one pyrometer.

The following models can be used to measure a variety of metals: steel rod & wire, forging, rolling, induction heating and heat treating; refractory bricks, carbon/graphite, viewing through hot combustion gases & flame, and many other applications.

The following models use a fiber optic cable to locate a small lens at up to a 5 meter distance from the pyrometer's electronics housing. The fiber cable and lense withstand up to 180 °C ambient temperature, can fit into tight spaces, and can withstand shock and vibration far better than electronics.

Infrared Pyrometers for Specific Applications

Glass Temperature Measurement Solutions

There are many different glass industry applications and processes which make use of pyrometers for non-contact temperature measurement.  The applications include:

In general, shorter wavelength spectral ranges penetrate the surface of glass to measure below the surface.  Greater than 5 micron spectral ranges are used for glass surface measurement.  The optimal spectral range for measuring glass surface temperature while viewing through hot combustion gas or flame is 5 microns.

A narrow-band spectral range near 8 microns is for the least penetration into the surface and thus for measuring the thinnest glass.  A narrow-band near 8 microns is also where the reflectivity of glass is the lowest.  An 8..14 micron spectral range is typically used for the lowest surface temperature measurement applications but there is 15% reflectivity to consider related to background temperature reflecting off the glass surface.

Thin Film Polymer Measurement Solutions

There are a variety of polymers used for creating thin film plastics.  "Thin" generally means a thickness less than 20...40 mils for the purpose of measuring temperature with an IR thermometer.

Hydrocarbon-based polymers such as Polythylene, Polypropylene and Polystyrene emit infrared best at 3.43. microns and to a lesser extent at 6.8 microns.  Polyesters, PTFE and Polyimides emit infrared best near 8 microns.

Decades of successful infrared thermometer applications for thin film measurements include film casting, stretching, extruding, extrusion-coating, coating, laminating, thermoforming and converting.

Combustion Gas Temperature Measurement

Pyrometers are used for gas temperature measurement in order to ensure environmental compliance, as well as for fire zone/combustion control within the boiler or incinerator. Additionally, infrared pyrometers allow the optimization of temperature to reduce nitrogen oxides (NOx) in Selective Non-Catalytic Converter (SNCR) systems.

HEITRONICS pyrometer solutions are installed in Municipal Solid Waste (MSW)/Waste to Energy (WTE) and Biomass WTE facilities, Hazardous Waste Incinerators, and Fossil Fuel Utility Boilers.

Hot combustion gas emits infrared at specific wavelengths depending on temperature, the materials being burned, and the resulting concentration of the by-products of combustion.  In all cases, high temperature gas is measured with an infrared pyrometer using the infrared energy received from a depth or column of gases within the sight path.
 

Infrared Calibration Equipment

Transfer Standards

Nearly all manufacturers of infrared temperature measuring instruments will utilize transfer radiation thermometers to acquire the radiated temperature from the radiation source.  This acquired temperature of the radiation source is then used to calibrate other instruments under test. To simply rely upon the temperature displayed on the controller of a typical commercially-available radiation source will add uncertainty. The use of a certified and qualified Transfer Standard provides the opportunity to reduce uncertainty when properly applied in a Scheme II calibration method.

Client users who own cavity blackbodies or plate radiation sources have historically sent them out for calibration or re-certification. The transportation of a radiation source adds risk due to shock and vibration during transit. A worst case scenario can occur after the radiation source has been re-certified and is then subjected to shock and vibration during return transport.

If the shock and vibration alters the location of heating elements or the location of the internal temperature sensor used for control, the temperatures can be offset without the client knowing. The use of a transfer standard overcomes such a risk. A transfer standard is much better suited for transportation when it requires calibration. The radiation source is better suited to be kept in the lab, permanently. Using a transfer standard which has the same or close to the same spectral range as the instrument under test typically provides the opportunity for best resulting uncertainty.

There are many parameters and conditions to be considered in the area of infrared calibration.  Wintronics is available to provide in-depth consultation on infrared calibration for your specific industrial application.

Blackbody Radiation Sources

Infrared Calibrators Constructed with High Emissivity Cavity

HEITRONICS offers blackbodies constructed with a cavity. A properly sized and shaped cavity provides the opportunity for achieving the highest emissivity. The higher the emissivity of the cavity, the better the uncertainty will be for this component of the total uncertainty calculation. HEITRONICS does not make plate radiation sources which typically have a large size of source area.
 

Plate radiation sources are typically specified with emissivity 0.95 ... 0.96. They are the best choice for calibrating low cost 8 ... 14 micron portable thermometers due to the wide Field of View (FOV) of such low cost thermometers.