Ultrasonic Sensor: Testing and Inspection
ULTRASONIC SENSOROPERATION PRINCIPLE
The sensor emits ultrasonic wave to the objects, and it measures the time until reflected wave returns, and calculates the distance to the object.
DISTANCE DETECTION TYPE
Direct detection type and indirect detection type are used together for improving effectiveness of the detection.
1. Direct detection type : One sensor transmits and receives signals to measure the distance.
2. Indirect detection type: One sensor transmits signals and the other sensor receives the signals to measure the distance.
MEASUREMENT PRINCIPLE
Back warning system (BWS) is a complementary device for reversing. BWS detects objects behind vehicle and provides the driver with buzzer alarm finding objects in a certain area, using ultrasonic wave propagation speed and time.
The propagation speed formula of ultrasonic wave in air is following:
NOTE:
1. 14 cm (dia.) plastic rod is used for the test target.
2. The test result may differ by a different target object.
3. Detection range may be reduced by dirt accumulated on sensor, and extremely hot or cold weather
4. The following object may not be detected.
- Sharp object or thin object like rope.
- Cotton sponge, snow or other materials absorbing sonic wave.
- Smaller objects than 14 cm (dia.), In length
v=331.5 + 0.6t (m/s)
v=ultrasonic wave propagation speed
t=ambient temperature
The basic principle of distance measurement using ultrasonic wave
WARNING
1. Range detected by back sensors is limited. Watch back before reversing.
2. There is a blind spot below the bumper. Low objects (for example boundary barrier) may be detected from minimum 1.2 m away unable to detect at nearer.
3. Besides there are some materials unable to be detected even in detection range as follows.
1. Needles, ropes, rods, or other thin objects
2. Cotton, snow and other material absorbing ultrasonic wave
(for example, fire extinguisher device covered with snow)
3. Reversing toward the sloped walls.
4. Reversing toward the sloped terrain.
4. False alarm may operate in the following condition: irregular road surface, gravel road, sloped road, grass. Upon alarm generation by grass the alarm may be generated by rock behind grass. Be sure to check for the safety.
Back monitoring sensor cannot discriminate among glass, stake, and rock.
5. Sensors may not operate correctly in the below conditions.
Ensure sensors clean from mud or dirt.
When spraying the bumper, the sensor opening should be covered with something in order not to be contaminated.
1. If sensor opening is contaminated with mud, snow, or dirt, detection range will be reduced and alarm may not be generated under the crash condition. Dirt accumulated on the sensor opening shall be removed with water.
Do not wipe or scrape sensor with a rod or a hard object.
2. If the sensor is frozen, alarm may not operate until sensor thaws.
3. If a vehicle stays under extremely hot or cold environment, the detection range may be reduced. It will be restored at the normal temperature.
4. When heavy cargo is loaded in trunk, it changes the vehicle balance, which reduces the detection range.
5. When other vehicle's horn, motorcycle engine noise, or other ultra-sonic wave sources are near.
6. Under heavy rain.
7. When reversing towards a vertical wall and the gap between the vehicle and the wall is 15 cm. (Alarm may sound despite of no barrier)
8. If radio antenna is installed at the rear.
9. If the vehicle rear wiring is re-routed or and electrical component is added at the rear part.
10. Vehicle balance is changed due to the replacement of the rear spring.
11. The unit will operate normally when the vehicle speed is 5 km/h or less. Above the speed, the unit may not operate normally.
6. Check the rear bumper for installation condition and deformation. If installed improperly or the sensor orientation is deviated, it may cause malfunction.
7. Be careful not to apply shock during sensor installation on the transmission or reception unit.
8. When adding electrical devices or modifying harness at the rear body of the vehicle, ensure not the change the transmission and reception unit wiring. Tagging the transmission side and reception side, it may cause malfunction.
9. High power radio transmitter (above 10 W) may cause malfunction. Do not install it on the vehicle.
10. Be careful that heating or sharp objects shall not touch BWS ultrasonic sensor surface.
Besides do not cover the sensor opening or press the sensor.