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How Does It Work?

The LED source is pulsed at a rate of approximately 100,000 pulses per second. The light pulses

propagate through the detection area and reflected light is captured by the optics and the

photodetector. The sensor signal is amplified and the signal acquisition is synchronized to the

pulses.

An oversampling scheme using multiple light pulses is implemented to improve the resolution of

the acquired signal. Typical oversampling values are 4 or 8 which produces a digitized signal with

an increased number of samples for improved accuracy and precision. In addition to

oversampling, an accumulation process is accomplished in order to improve the signal to noise

ratio. The oversampling value and number of accumulations influence the

detection/measurement, the range, accuracy and precision of the measurements.

The performance of the sensor can thus be optimized with these parameters to meet the

requirements of the application.

Detection and Distance Measurement

The detection and distance measurement is performed by the sensor’s processor, using the

acquired signals (one per photodetector element). The signals consist of a series of values

representing light amplitude at incremental distances from the sensor. The number of samples

in the signal is chosen according to maximum range required.

The amplitude of each sample is an indicator of the quantity of light reflected back from a given

object at that specific distance. The amplitude depends on distance, size, reflectivity and angle

of the object with respect to the sensor.

An object will be detected by the sensor if a light pulse above a predetermined threshold is

found. The threshold at which a peak in the trace is interpreted as the presence of an object

depends on the signal-to-noise ratio. LeddarTech determines the default threshold level for

each sensor based on the signal-to-noise ratio. A threshold table is applied in the detection

processing of the traces, and a threshold offset parameter is provided on most sensors in order

to adjust this threshold table. The offset can be set to increase or decrease the sensitivity of the

sensor. This can be used to ignore the presence of objects returning weak signals or to maximize

detection of such objects and filter false detections in the application software.

Another setting available on Leddar sensors is the LED intensity. LED intensity control can be set

to manual mode or automatic mode. In manual control mode, the setting is adjusted by the

operator to best fit the application. In automatic control mode, the sensor will dynamically

adjust the LED intensity based on the amplitude of the signal for objects detected in the sensor

beam. With this control, a sensor model can be used for a wide range of applications with

different range requirements and also be used in applications where objects can both be very

close or far from the sensor.