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DELTA LTL2000S(Q) Retroreflectometer 17
Instrument function
Physically the instrument is dominated by the “control tower”. The tower contains the Rl il-
luminating and observation system and the control electronics.
The unit on top of the base structure contains the Qd illumination system, the observation sys-
tem is the same for both Rl and Qd.
The base structure contains an optical system with mirrors that directs Rl illumination beam
towards the road surface and the Rl or Qd signal to the detector through a dust-protection
window. The measuring area is shielded by an aluminium housing.
The instrument is controlled by a microprocessor that executes the measurement automatical-
ly by the push of a button and presents the result on a display. The result is automatically
transferred to an internal non-volatile memory. The result and corresponding measurement id,
time and date can be printed by the built-in printer. The LTL2000S(Q) is operated with a
small keyboard located at the top of the Retroreflectometer. Further, Retroreflectometer con-
trol is possible over a serial communication link (RS232). Stored data can easily be trans-
ferred to a host PC for further processing.
The LTL2000S(Q) is powered by a built-in lead acid battery, which under normal operation
will keep the Retroreflectometer operating a normal working day. The battery is recharged by
use of an external charger.
Factory calibration
The LTL2000S(Q) Retroreflectometer is factory calibrated. This calibration is carried out by
using calibration units mounted in specially designed frames. The calibration unit's values are
measured in the laboratory using traceable methods and equipment.
Notes on error sources
Stray light can enter the instrument between the skirts and the road. Leakage will under nor-
mal measurement conditions not be significant. Nevertheless it may occur. Before each meas-
urement the LTL2000S(Q) automatically evaluates the leakage and the result is compensated
before read out. In case of a significant leakage level a warning or error message is given and
special precautions such as screening 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 light trap, the dust-protection window
and the ceramics on the calibration unit clean. Especially the light trap is critical.
The LTL2000S(Q) 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 irregu-
larities.
The LTL2000S(Q) must be parallel with and close to the road.
The LTL2000S(Q) Retroreflectometer is a rugged instrument, but it is an optical instrument
and must be handled as such.