14 RetroSign GR1 & GR3 · Retroreflectometer
Section 3 – General Information
RetroSign GR1 & GR3
The RetroSign Retroreflectometer measures the R
A
(coefficient of retroreflected luminance) parameter. The R’ parameter
represents the retroreflection of the road signs seen by drivers of motor vehicles by headlight illumination.
Physically the Retroreflectometer is a small hand held instrument. It is constructed in aluminum housing, containing elec-
tronics and an optical system. The measurement trigger button and the replaceable battery are housed in the handle.
The RetroSign is controlled by a micro controller that executes a measurement automatically when the trigger is acti-
vated. The result and status are shown on the LCD display. The result and other related information is automatically
transferred to the internal non-volatile memory. The RetroSign is operated from a small keyboard on the left hand side of
the Retroreflectometer. The Retroreflectometer control is also possible using a USB device connection. The USB con-
nection is used to transfer data records to a PC for further processing.
Factory calibrations
The RetroSign GR1 and GR3 is factory calibrated. This calibration is carried out using a standard. The reference’s R
A
value is measured in the laboratory using traceable methods and equipment.
The enclosed reference cap should be used for verification and recalibration of the Retroreflectometer.
Measurement geometry
GR1 and GR3 type ASTM
The illumination angle is -4°. The offsets between the illumination and the primary observation angle are 0.2° (GR1) and
the three observation angles are 0.2°, 0.5°and 1.0° (GR3) respectively. The measurement area is approx. ø 30 mm. in
the standard configuration, ø 15 mm or ø 10 mm when using the reduced aperture adaptors.
ASTM geometry
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