Delta PG-35 Specifications download pdf (Page 13)

DELTA LTL-XL Retroreflectometer 13

SECTION 2

GENERAL INFORMATION

The measurement

The LTL-XL retroreflectometer measures the R

(coefficient of retroreflected luminance) pa-

rameter and Qd (the day light visibility). The R

parameter represents the brightness of road

markings seen by drivers of motor vehicles by headlight illumination. Qd measures the visi-

bility of the road markings under day light conditions.

In the LTL-XL the illumination angle is 1.24 degrees for R

, the illumination for Qd is dif-

fuse. Both observation angles are 2.29 degrees. According to both ASTM and CEN standards

these angle simulates a driver’s viewing distance of 30 meters. The instrument’s illumination

field is approximately 185 mm x 50 mm / 1.97 x 7.28 inch.

The LTL-XL is controlled by multiple microprocessors. It is operated with an extractable

keyboard located at the top of the retroreflectometer. It executes the measurement automati-

cally by a push of the green button and presents the result on a display. The result is automati-

cally transferred to the internal memory. The measurement, along with its corresponding time,

date, and other data can be printed using a printer (optional).

Optical principle

The optical system in the LTL-XL is covered by a patent. A LED lamp in the top of the tower

generates the light for the R

measurements. After a field stop the light is collimated by a lens

and deflected through a mirror toward the road. The diffuse Qd illumination is based on an

array of LED’s.

The reflected light from the road uses the same mirror and lens. Between the lens and the pho-

to detector field aperture, stops define the observation area. The illumination field is inside in

the observation field. This is important to assure correct measurement on profiled markings.



spectral correction is achieved by use of advanced optical filters.

Notes on error sources

Stray light can occasionally enter the instrument but will be insignificant under normal meas-

urement conditions. Before each measurement, the LTL-XL automatically evaluates the leak-

age and compensates for it before the readout. In case of a significant leakage level, a warning

or error message is given and special precautions may be necessary.

Instrument leak, drift and offset errors are compensated by means of data obtained during the

calibration procedure. It is very important to keep the dust-protection window and the ceramic

on the calibration unit clean.

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Delta PG-35 Specifications Page 13