Low Temperature Black Bodies for Calibration and Characterization of Near Ambient Devices

Low temperature black bodies are useful for calibrating and characterizing near ambient devices. Typical low temperature black body components are shown in Figure 1. The melting point of working metal Ga or In controls the operating temperatures of the fixed operating point units, which provide absolute temperature with high accuracy. The variable temperature unit provides greater versatility.

Typical Low Temperature Black Body Components

Figure 1. Typical Low Temperature Black Body Components

A temperature controlled recirculating bath is required for all three of these devices as a source of partial or full temperature control. It is necessary to select the appropriate working fluid to match the operating temperature range. The devices also rely on vacuum for insulation. Each unit is supplied with appropriate vacuum equipment and recirculating bath. Optimum stability/reproducibility is achievable through the use of black body cavities in air or under vacuum.

Fixed Point Black Bodies

The fixed point devices use high purity, low melting point metals, Ga (62501) and In (62502), for establishing their operating temperature. In normal use, slow melting (solidification) of the metal load takes place by circulating the working liquid at a temperature just above (below) the melting point. In this way, the black body cavity made of Teflon is maintained exactly at the melting point temperature until the existence of both solid and melted phases. Several hours of continuous operation are possible. Schematic of 62501 Ga Fixed Temperature Black Body is shown in Figure 2.

Schematic of 62501 Ga Fixed Temperature Black Body

Figure 2. Schematic of 62501 Ga Fixed Temperature Black Body

Variable Temperature Black Body

Model 62503 is a variable temperature black body that gets its operating temperature from the recirculating bath and high accuracy platinum resistance thermometer system. The radiating cavity is made within a solid copper block to achieve optimum heat transfer. The specifications of the variable temperature black body are summarized as follows:

Operating temperature :
   Ga Black Body : 302.915K
   In Black Body : 429.75K
   Variable Temp. Black Body : 293 - 473K
Temperature repeatability :
   Ga Black Body : 0.2mK
   In Black Body : 50mK
   Variable Temp. Black Body : 20mK
Operating environment : Vacuum or air
Cavity diameter :
   Ga and In Black Bodies : 1.2 inch (30mm)
   Variable Temp. Black Body : 1.6 inch (40mm)
Cavity length :
   Ga and In Black Bodies : 7 inch (180mm)
   Variable Temp. Black Body : 9.8 inch (250mm)
Outer aperture diameter :
   Ga and In Black Bodies : 0.8 inch (20mm)
   Variable Temp. Black Body : 1.2 inch (30mm)
Effective emissivity at 1µm :
   Ga and In Black Bodies : 0.9999
   Variable Temp. Black Body : 0.999
Load (Ga and In models, only) : 2.5kG
Purity (Ga and In models only) : 0.9999999 (Ga)
0.999999 (In)
Outer dimensions/weight :
   Ga and In Black Bodies : 6.7 inch diameter x 14.4 inch long (170mm diameter x 365mm long)
33lbs (15 kg) (Black Body, only)
   Variable Temp. Black Body : 6.7 inch diameter x 16.5 inch long (170mm diameter x 420mm long)
7.7 lbs (17 kg) (Black Body, only)

All systems comprise a black body and temperature measurement/stabilization components, a recirculating cooler, appropriate working liquid, and a vacuum setup.

Transfer Standard Pyrometer

The new 62512 Transfer Standard Pyrometer can be used to set/measure the temperature of the 62500 High Temperature Black Body. It is essential to calibrate the pyrometer prior to its application or its use for transferring calibration from a color temperature standard lamp. The 62512 is supplied with a high temperature detector set (1400 - 2900K). A lower temperature optical head can be purchased upon request. Transfer Standard Pyrometer comprises optical unit, temperature controller, amplifier and precision multimeter. The specifications of a transfer standard pyrometer are as follows:

Temperature range : 600 - 2900°C
Minimal spot size : 0.6 x 0.8mm
Effective wavelength : 650nm
Stray light rejection : 10-6
Resolution/short term stability : 25mK
Long term stability :
   At 1400 - 2900°C : 0.03%
   At 900 - 1400°C : 0.05%
   At 600 - 900°C : 0.1%

The key features of Transfer Standard Pyrometer are as follows:

  • Achromatic optics
  • Electronic shutter
  • Minimum spot size, 0.6 x 0.8mm
  • Thermo stabilized detector and filter
  • Long term stability to 0.03%
  • 25mK resolution/short term stability
  • 900 to 3200K range

Precision Apertures

The new 8mm diameter precision apertures can be used to gain insights into a black body source. Emitting area knowledge, coupled with emissivity and temperature values completely describes a black body source. The specifications of precision apertures are as follows:

Material : Phosphorus bronze
Coating : Au
Aperture diameter : 8 ±0.1mm
Departure from circularity : 0.2µm
Peak to valley variation : 0.5µm
Diameter measurement : 0.5µm (2σ)
Outer diameter : 40 - 0.1mm
Thickness : 6mm
Nominal cone angle : 57°

About Oriel Instruments

Oriel Instruments, a Newport Corporation brand, was founded in 1969 and quickly gained a reputation as an innovative supplier of products for the making and measuring of light. Today, the Oriel brand represents leading instruments, such as light sources covering a broad range from UV to IR, pulsed or continuous, and low to high power.

Oriel also offers monochromators and spectrographs as well as flexible FT-IR spectrometers, which make it easy for users across many industries to build instruments for specific applications. Oriel is also a leader in the area of Photovoltaics with its offering of solar simulators that allow you to simulate hours of solar radiation in minutes. Oriel continues to bring innovative products and solutions to Newport customers around the world.

This information has been sourced, reviewed and adapted from materials provided by Oriel Instruments.

For more information on this source, please visit Oriel Instruments.

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