ASTECH LDS10A, User Manual, Page: 20 / 36

Start-up and measurement principle LDS10A Manual
Page 20 ASTECH GmbH
6.2 Measurement principle
The measurement principle of the LDS10A consists of a number of separate
data acquisition and processing algorithms.
Signal Acquisition
The signal acquisition module samples the signal of the photodiode element
using a patented oversampling and accumulation strategy to maximize the
signal resolution and the signal to noise ratio. It provides the light intensity
received by the sensor as a function of the time (corresponding to distance
knowing the speed of light) also called full-waveform signal. This full-
waveform signal allows the use of advanced signal processing techniques to
extract the distances of the objects and other useful information about the
scene.
Static Noise Removal
The static noise removal algorithm removes, as its name indicates, the static
noise in the full-waveform signal induced by undesirable light reflections due
to sensor enclosure or electromagnetic interferences. This algorithm increases
drastically the distance measurement accuracy and linearity. The static noise
shape is learned during a calibration procedure during which the waveform of
the signal is captured while the reception lens of the sensor is shielded from
the backscattered light. The sensor comes with a static noise factory
calibration.
Pulse Detection
The objects in the sensor field of detection create a particular signature in the
full-waveform signal called pulses. The pulse detector analyses the full-
waveform signal in order to recognize these pulses and compute their
distance. By nature, time-of-flight sensor using full-waveform analysis is able
to detect several distinct objects with a single photodiode element.
The detected pulses have specific amplitudes based on their distance from the
sensor and on the reflectivity of the objects. It is well known that pulses of
small amplitudes do not lead to accurate and precise distance measurements.
Consequently, the algorithm removes all pulses with amplitudes under a given
threshold.