Delta LTL2000S - Manual (Page 16)

DELTA LTL2000S(Q) Retroreflectometer 12
The illuminations field with a length of 200mm length and 43 mm wide gives a large measur-
ing measurement field of 85 cm
2 . Combined with an observation field of 350 mm length this
gives a considerable capability to measure profiled and textures makings but also a high reli-
ability for obtaining correct readings for un even surfaces or if small debris are present at one
of the instruments support pads on the marking.
Because of illumination at an angle of only 1,24
° to the surface in the CEN-Prescribed ge-
ometry, the illuminated patch moves ahead by 46 mm for each mm lift of the instrument (1
mm/sin 1,24
° = 46 mm). A shift might affect the readings, when the tape is not completely
uniform. Therefore, to avoid the shift, the instrument is moved backwards by 46 mm for each
mm lift.
Refer to figure 3 for results of the measurements. The R
L
value is roughly constant up to the
height of 4 mm, but at 5 mm there is some reduction.
To understand this, one needs to know that the illuminated patch moves by 46 mm per mm,
but the measurement area by only 25 mm per mm at the measuring angle of 2,29
° relative to
the surface (1 mm/sin 2,29 ° = 25 mm). The measuring area is larger than the illuminated
patch, and contains it, but at some lift the illuminated patch moves partly out of the measured
area - causing reduction of the measured R
L
value.
On the basis of these measurements, it can be claimed that this particular instrument has a
reach of almost 5 mm down into a profiled road marking, and the corresponding 5
×46 mm =
23 cm reach along gaps. This reach is assumed to be 20 cm to be on the safe side.
The significance is that the instrument can readily be used to measure the R
L
of profiled road
markings, when the profiles are at most 5 mm high, or gaps between profiles are at most 20
cm. Refer to figure 5 page 14.
In practice, it is necessary to take readings at a number of positions covering one or more pro-
files. There may be variation with the position, but the average value will reflect the true R
L
value of the profiled road marking as experienced by a driver at night.
Most of profiled road markings used on roads in Europe can be measured with the LTL
2000S(Q), and are in fact measured with the LTL2000 as a matter of routine. Examples are
'Spotflex', Longflex', 'Rainline' and 'Drop-on line'.
FOR MARKINGS EXCEEDING 5 MM HEIGHT/200 MM IN SPACING PLEASE
CONTACT DELTA.