Vehicular Sensor Networks: General Aspects and Implementation Issues - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 219

Distance Sensors

Distance sensors measure the distance from the sensor to a target object. Based on
the measurement method, their classification is given in Table 10.2 . Special interest
for intra-vehicle implementation lies in the radar, laser, and ultrasonic sensors. The
distance is determined by sending out ultrasonic pulses and listening for the return-
ing echoes reflected from the target. Thus, the use of the Doppler effect is prevalent
again as in the case of speed measurement sensors. The time from transmissions to
return of an echo is the basis of obtaining the distance measurement. Nowadays,
instead of sound (ultrasound), this method is used with electromagnetic waves and
light or laser. It is important to understand that the wave frequency takes an impor-
tant role in the distance measurement.
Table 10.3 gives a comparison of three ultrasonic sensors. As anticipated, an
increase in device dimensions leads to an increase in their performances like range,

Table 10.2 Distance sensor classiication
Distance sensors
Long distances

Short distances

• Radar • LVDT

• Ultrasonic • Triangulationlaser

• Longdistancelaser • Profilescannerlaser

• Bycable • Potentiometer

• Magnetoresistive • Magnetorestrictive

• Digital

Table 10.3 Distance sensor's characteristic
SR50 SA6A SRF235

Power consumption
(mA)

2-250 10 25

Measurement range (cm) 50-1,000 20-200 10-120

Response time (ms) 60 48-90 ?

Dimensions (mm) 310 × 75 × 75 84.5 × 50 × 29 34 × 20 × 19

Weight (g) 1,300 270 6