performance index test of Ultrasonic sensor technology

Ultrasonic sensor detection technology

The ultrasonic transducers are a piezoelectric ceramic device that realizes bidirectional conversion of mechanical energy and electrical energy through a piezoelectric effect. Its propagation speed is 344m / s (25 degrees). The operating frequency is generally between 20kHz and 200kHz. The distance and relative velocity of obstacles are determined by reflection and doppler effect. The detection distance is generally between 1 m and 2 m. It is widely used in product systems such as reversing sonar, anti-theft alarm, flow meter, parking timing, and automatic door. The detailed workflow of the ultrasonic sensor system as follows: the controller drives the ultrasonic sensor (transceiver integrated and integrated) through the driving circuit to generate a short, fixed-frequency ultrasonic signal through piezoelectric conversion, when the ultrasonic pulse encounters an obstacle. The reflection will occur, the receiving sensor will receive the reflected mechanical echo, and then through the piezoelectric transformation, after the echo electrical signal is processed by amplification, filtering, detection, etc., according to the transmitted ultrasonic wave and the received reflected echo. The time interval is calculated to the distance between the sensor and the obstacle. The following is some of its main parameters: Sound pressure characteristics, sound pressure (SPL) is a parameter indicating the volume of the sensor's emission. It is expressed by the following formula: SPL=20logP/Pre(dB) “P” is the effective sound pressure, “Pre” is the reference sound pressure (2×10-4ubar), and the sound pressure of the ultrasonic sensor is generally ≧100dB.

Sensitivity is a parameter indicating the strength of the sensor's receiving capability. It is expressed by the following formula: 20 log E/P (dB) "E" is the generated voltage value (VRMS), and "P" is the input sound pressure (ubar). The sensitivity of the ultrasonic distance sensor is generally -60dB~-85dB. The detectable area of the detection envelope sensor is irregular, generally the strongest at the back, the farther the distance is, the faster the attenuation; the reflection of the oblique direction is weak, the overall detectable area is fanned. The inspection process of conventional ultrasonic sensors is as follows

1. Set a shielding box, put a standard test rod in the farthest detection distance position (1.5m ~ 2m) specified in the shielding box, generally ¢75mm PVC pipe, put the sensor module to be debugged into the test frame ,it is connecting the oscilloscope.

2. Power on the system, adjusting the adjustable mid-week of the sensor board, so that the equivalent capacitance inside the middle and the sensor will generate resonance at a specific frequency and reach the optimal point; then debug the echo sensitivity of the distance measuring transducer sensor (generally through the adjustable resistor) ), observe the echo width of the obstacle through the oscilloscope to the required value.

3. 
    The standard test rod is moved by the motor to move the effective detection distance to observe the change of the echo width of the obstacle. At the same time, the buzzer will report different audible warnings according to different distances. For the traditional ultrasonic sensor test can only consider whether the sensor's ranging function, this measurement mode is judged by the change of the material and surface finish of the PVC pipe; and for the performance index of the sensor such as the sound pressure, the receiving sensitivity .There is no quantitative detection and determination of the detection envelope range; and the ranging is realized based on the reflection of the PVC pipe, resulting in a large error in the parameter consistency of the product. The present invention proposes the following detection methods:

   
   1. After completing the sensor ranging function test, to verify the sound pressure and envelope range of the ultrasonic range finding sensor. The sensor can continuously emit ultrasonic waves in this mode; five spatially distributed high-frequency microphones are set outside a certain horizontal distance (30-40 cm) from the test sensor, and the ultrasonic signals emitted by the sensors are collected by five high-frequency microphones to judge and analyze. The sound pressure level of the ultrasonic wave and the position of the microphone calibration determine whether the sensor beam angle (envelope range) meets the index requirements.

   
   2. After completing the above test, the sensor's receiving sensitivity index test is performed. The sensor enters the continuous receiving state in this mode, and sets a transmitting sensor outside a certain horizontal distance (30 to 40 cm). The transmitting sensor emits an ultrasonic signal that calibrates a certain sound pressure level (simulating the echo signal intensity emitted by the obstacle), and the ultrasonic signal emitted by the transmitting sensor is received by the receiving sensor to be tested, and the piezoelectric conversion and signal amplification are performed in the sensor. Then connect to the acquisition card for data analysis, analyze whether the sensor can receive the echo signal under the sensitivity condition, and test whether the sensor receiving sensitivity meets the test index requirements.

     
   3. Manufacture a shielding box for testing the working of ultrasonic distance sensor
   . The inside of the box is covered with sound-absorbing cotton to prevent interference from other sound waves during testing. There are fixtures for sensor test position in the box. There are 5 high-frequency microphones and one at the bottom of the box. About launch sensor. They are used to test the sound pressure, envelope range and echo sensitivity of the ultrasonic sensor to be tested.

           
   4. The sensor needs to have three test modes, which can realize mode conversion by communicating with the host.  

                   
   5, Continuous transmission mode, in which the sensor can continuously emit ultrasonic waves through the test without echo reception; in this mode, the ultrasonic signals emitted by the sensors are collected by five high-frequency microphones to judge the sound pressure of the ultrasonic waves. The level and the position of the microphone calibration determine whether the sensor beam angle meets the index requirements.