SHENZHEN LONGSUN ACOUSTIC CO., LTD.

Ultrasonic transducer is used in traffic flow detector based on its main characteristics, more important, it has obvious advantages over electromagnetic pressure sensor in traffic flow detector:

* Easy installation and maintenance;

* Can work under all kinds of weather condition;

* No need to bury under the road, it is cost effective.

Ultrasonic traffic detector consists of emitting and receiving system, ultrasonic transducer, signal process system etc, its working principle is based on ultrasonic ranging (see details please refer to earlier ultrasonic distance test in other article). 

(Illustrated system layout see figure 6-1) 

Figure 6-1

Illustrated system layout

Ultrasonic traffic detector can tell vehicle height, length and running speed to confirm the type of vehicle through its ultrasonic ranging and compared with data base of vehicle characteristics for all kinds. 

Vehicle height measurement

Traffic flow diagram (Figure 6-2)

We installed two ultrasonic transducers above the road at "H" meter place with "L" meter distance between them  ( see figure 6-2). Ultrasonic pulse emitted from transducer travels in the air to reach the top of vehicle at sound velocity, ultrasonic pulse bounced back to the transducer once touching vehicle top. Provided "C" is sound speed, "t" is time takes by transducer emitting and receiving ultrasonic pulse, "D" is the height of vehicle, and then we can know the vehicle height through the following formula:

D=H - Ct/2                                             (1)

Vehicle speed measurement

From Figure 6-2, given the vehicle runs from transducer 1 to transducer 2 at "V" speed, if "t₁" is time takes the vehicle reaches the place under the transducer 1, "t₂" is the vehicle arrives at the place under transducer 2. Since 'L" is constant we already have, we can know the vehicle speed is:

V=L/(t₂-t₁)=L/△t₁                                (2)

Vehicle length measurement

If we  know the time takes by the whole vehicle passed through one transducer, we can calculate the vehicle length. Provided "△t₂" _{is time takes by the vehicle continously passes through one transducer, "S" is the vehicle length. Given "Th" the vehicle head reaches the place under transducer, "Tr" the rear of vehicle arrives at the transducer, and then the vehicle length is:}

_S=V*△t2=L/△t_{1*△t2                                          (3)}

_{Vehicle classification and measurement}

Normally, the vehicle classification please refer to figure 6-3 below:

Figure 6-3

We can use ultrasonic transducer to detect the vehicle height, length as well as speed to adjust the layout of the vehicle passing through the traffic detector and compare with our data base which has main characteristics about car, jeep, truck etc to tell the traffic flow for all kinds of vehicle at fixed period, in order to let traffic department to monitor and control the traffic situation to alert the driver.