Agera Instrument Standard for TOP of Scale

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(PTFE versus White Pigment)

In the CIE 15 it is recommended to use the Perfect Reflecting Diffuser (PRD) to set the Full Scale or Top of Scale (TOS) standardization for the instrument.   CIE 15 recommends using either Barium Sulfate or PTFE calibrated to the PRD for the geometry of the instrument.   ASTM allows a user to use the standard supplied by the instrument manufacturer provided that the standard has been calibrated relative to the PRD.  This allows any white object that is properly calibrated to be used as the Instrument standard.

Technical comparison of Agera Instrument Standard to LabScanXE instrument Standard.   

The LabScanXE uses an enameled porcelain on steel 4” square tile to set the TOS.  This type of standard is extremely durable as it is basically a powdered glass that is pigmented white then melted onto a steel plate producing an extremely hard scratch resistant surface that is easy to clean.  The Agera uses a PTFE based coating that is sprayed onto a steel disc.   PTFE is hydrophobic, and has an extremely low ecoefficience of friction, meaning most things won’t stick to or be absorbed into the PTFE which does not have a surface that is as hard as porcelain steel.  The PTFE disc is mounted recessed in a proctective aluminum puck such that when placed face down on a table the PTFE surface does not touch the tabletop.  The Agera TOS while slightly less durable than the LabScanXE TOS has a large advantage in that its reflectance is very close to that of the PRD.  See graph below

The LabScanXE TOS has an average reflectance of 85% from 420nm to 700nm while the Agera TOS has an average reflectance of greater than 95% from 400nm to 410nm and greater than 97% from 430nm to 700nm. 

 

The LabScanXE TOS has an average 60o Gloss of greater than 70-90 GU and the Agera TOS has an average 60o Gloss of 2.6- 3.0 GU

Handling, Care and Cleaning of Instrument Standard.

The Agera TOS is an an optical coating and should be handled in much the same way as other optical surfaces. Although the material is very durable, care should be taken to prevent contaminants such as finger oils from contacting the material’s surface.  If the surface appears lightly soiled, it may be air brushed with a jet of clean dry air or nitrogen. DO NOT use Freon. For heavier soil, the material can be cleaned by scrubbing with a soft brush under running water. Blow dry with clean air or nitrogen or allow the material to air dry. If the material is heavily stained, soak with either an extremely mild mix of soap and water, 5% white distilled vinegar, or hydrogen peroxide. Then run under water while scrubbing with a soft brush.

 

 

 

Using Diagnostic Check tile to confirm suitability of Instrument White tile.

 

If a user is concerned that an Agera TOS standard has been scratched or dimpled or discolored and they are not sure if the standard is still usable after cleaning then they should do the following tests.

  1. Measure the 60o Gloss value. If the result is between 2.5 and 3.5 the surface is still sufficiently diffuse.
  2. Perform the EasyMatchQC Diagnostics Check Tile test. If the Check tile reads within specification then the surface color of the TOS supplied the correct spectral response during standardization.

 

Replacement Options

If the Agera TOS is damaged or discolored such that cleaning per the instructions does not return the surface to a condition such that either of the  two Diagnostic checks fails then Contact HunterLab and request a replacement Instrument Standard.  This will include a new PTFE based disc pre mounted in a protective centering puck and a thumbdrive with a program to load the new white tile values into the Agera firmware.

 

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