Delta LTL-XL - General Information; Measurement Principles; Error Sources and Environmental Conditions

DELTA LTL-XL Retroreflectometer 13
SECTION 2
GENERAL INFORMATION
Measurements
The LTL-XL retroreflectometer measures the R
L
(coefficient of retroreflected luminance) pa-
rameter and Qd (the day light visibility). The R
L
parameter represents the brightness of road
markings seen by drivers of motor vehicles by headlight illumination. Qd represents the visi-
bility of the road markings under day light conditions.
In the LTL-XL the illumination angle is 1.24 degrees for R
L
, 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.
Push the button from the HOME screen to take a measurement. Shortly after, the R
L
and
related information are presented on the colour display. The result is automatically transferred
to the internal memory. The measurement, along with its corresponding time, date, and other
data can be printed using the (optional) built-in printer.
Every measurement contains status information. If an error occurs the information can be in-
terpreted by the warning/error icon in the top line of the display. The information is available
until a new measurement is taken. The status information is stored in the log.
Notes on error sources
Stray light can occasionally enter the instrument but will be insignificant under normal meas-
urement conditions. The LTL-XL compensates for stray light automatically.
Instrument drift and offset errors are compensated by means of data obtained during the cali-
bration procedure. It is very important to keep the dust-protection window and the ceramic on
the calibration unit clean.
The LTL-XL illumination angle is 1.24° relative to the road surface. Because of this small
angle accurate placement on the road is important. Avoid pebbles and abnormal irregularities.
The LTL-XL must be parallel and in contact with the marking surface.
The LTL-XL retroreflectometer is a rugged instrument, but it is an optical instrument and
must be handled as such.
The LTL-XL is factory calibrated. Nevertheless start measurements with a calibration. Study
the display for any warning or error icons. See also Section 4 - Maintenance
Note
Keep the dust-protection window and ceramics on the
calibration unit clean.
Keep the battery fully charged. A well charged battery is
more resistant to aging and damage.