Delta LTL2000S Dokumentacja Pobierz pdf (Strona 14)

DELTA LTL2000 Retrometer 8

The LTL2000 is controlled by a microprocessor. The microprocessor executes the measurement

automatically 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 time and date can be

printed by the built-in printer. The LTL2000 is operated with a small keyboard located at the top of the

Retrometer. Further, Retrometer control is possible over a serial communication link (RS232). Stored

data can easily be transferred to a host PC for further processing.

Factory calibration

The LTL2000 Retrometer is factory calibrated. This calibration is carried out by using a special

calibration unit and a specially designed base frame. The calibration unit's Rl value is measured in the

laboratory using traceable methods and equipment.

The enclosed calibration unit and base frame can be used for the control and re-calibration of the

Retrometer.

The LTL2000 is powered by a built-in lead acid battery, which under normal operation will keep the

Retrometer operating a normal working day. The battery is recharged by use of an external charger.

Optical principle

The light is generated by a halogen lamp placed at the top of the tower, see Appendix C - figure 23. The

light is focussed on a rectangular field stop and directed toward the illumination aperture at the front of

the lens. Hereafter the beam is collimated by the lens and directed toward the road by a 50% beam

splitter. The observation system is equivalent to the illuminating system. The reflected light enters the

detection system mirror which deflects the light trough the collimator lens and observation aperture to

the detector unit in top of the tower.

Observation field and angle are defined by field stops and apertures. The retro reflected light is collected

by the detection mirror and by the lens focussed on an optical fibre bundle. The light is by the optical

fibre bundle guided to an photo multiplier. An optical filter is placed in front of the photo multiplier to

obtain colour matching.

Notes on error sources

Stray light can enter the instrument between the rubber skirts and the road. Leakage will under normal

measurement conditions not be significant. Nevertheless it may occur. Before each measurement the

LTL2000 automatically evaluates the leakage. The result is compensated before read out. 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 light trap, the dust-protection window and the ceramics on

the calibration unit clean. Especially the light trap is critical.

The LTL2000 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 LTL2000 must be

parallel and close to the road.

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Delta LTL2000S Dokumentacja Strona 14