C03EN – Measurement results Classic

 How to understand the results.

A retroreflectometer can get results at CEN geometry (1.24 / 2.29 degree).
The ability of implement the CEN geometry could be checked by independent test laboratories. The Classic model is a certified instrument. You can download the test results HERE.

The measurements values depends of the calibration point, however there is not an UNIQUE reference standard for retroreflectance in the world.

There is no UNIQUE retroreflectance reference standard in the world.

  • The retroreflectance reference value is the result of an optical measurement in laboratory.
  • It could be found differences of 5% to 10% between different laboratories or different optical measurement methodologies.
  • The uncertain of any optical laboratory (NIST, METAS, IPT) is at least 5%. As it is obvious, any portable retroreflectometer should have a worst uncertainty – 10% typical .

As direct consequence, different instruments could have different calibration points; the measured values depends of that reference. The follow graphic illustrates a typical uncertainty situation .

calibration_diferences_GRAF

The shape of the curves is the same. It is a simple matter of referencing.

It is not correct to say that the instrument A is showing correct values . It is also not possible to say that the instrument C is 20% wrong. Both of them are showing correct values under the calibration uncertainty margin (10%).

How to adjust the calibration reference ?

All Easylux devices are calibrated at the lower uncertain range value of the reference laboratory (NIST, METAS, IPT). It allows you to make sure that readings represents the minimum trustable value for the road marking retroreflectance.

It is important to keep the calibration plate clean and protected inside its carrying bag. It is the calibration reference of your instrument. To ensure reliable measurements, periodic replacement of the reference plate is recommended.

The  calibration reference can be adjusted by the user to support special cases like:

  • Work with a secondary standard ( by a local laboratory, per example) as instrument reference.
  • Adjust the calibration point of your Easylux instrument to the upper side of the reference optical laboratory uncertain range (+5% / +10%).

To adjust the calibration point, go to the CONFIG menu.

 

classic_reference

classic_etiqueta
The red circle shows the Upper uncertain value.

 

Internal Reference

The coeffıcient of retroreflected luminance –  RL – is the ratio of the luminance by the illuminance at the surface on a plane normal to the incident light.  It  can only be determined by optical laboratory measurements of retroreflective road marking materials.

Portable retroreflectometers can implement the measurement geometry (EN 1436), however It can only make comparisons between the internal calibration reference and any light received from a test sample. It is a sophisticated optical comparator.

The standardization of a portable retroreflectometer directs impact the results.

Easylux retroreflectometers are standardized in factory with a panel of marking material with a known and reproducible coefficient of retroreflected luminance measured by optical laboratory at EN 1436/ ASTM E1710 geometry.  The optical laboratory measured value is under an uncertainty range of 10%. All Easylux instruments are standardized at the lower band uncertainty range value (-10%) by default. It allows you to make sure that readings represent the minimum trustable value for the road marking retroreflectance.

Uncertainty of measurement is the doubt that exists about the result of any measurement.

The following pictures illustrate the effect of the internal reference adjustments on measured results. The internal calibration reference can adjusteted around the uncertainty range .

Default Factory reference

ref_default`REF_CLASS_220

Default Factory reference + 10% uncertainty compensation

ref_10moreREF_CLASS_242

Wrong adjustment

ref_erradaREF_CLASS_50

 

 

 

 

Secondary reference plate or laboratory test samples.

It is a very popular practice use a retroreflective material secondary reference or a laboratory test plate to minimize uncertainty issues between different brands of retroreflectometers. They should be equalized with a unique and common traceable reference standard. It could be a local laboratory traceable secondary reference plate.