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Ultrasonic flaw detection principle and sensor test and design

ShenZhen OSENON Technology Co.,Ltd | Updated: Apr 17, 2018


Ultrasonic transducers, horns and sound covers are devices that convert electrical energy into vibration. To understand the principle of operation, comparisons can be made between ultrasonic welding machines and automobiles.

 

The sensor performs energy conversion (as a motor), the transformer adjusts the ratio between force and speed (eg, gearbox), and finally the ultrasonic/ultrasonic horn guides and applies this energy to complete the required work (as a wheel).

 

In an automobile, all mechanical system components must be well-designed and harmonically designed to maximize energy transfer efficiency. The same is true for ultrasound systems, but in this case, the key parameter for efficiency is the frequency of the components that should be as close as possible (for example, 20 kHz +/- 50 Hz).


Ultrasonic welding and automotive mechanical systems.gif

Ultrasonic welding and automotive mechanical systems


operating

 

The sensor has two operating frequencies and can be easily identified in its electrical impedance curve. The maximum impedance corresponds to the anti-resonant frequency (maximum speed). Ultrasonic welding systems work at anti-resonant frequencies. The minimum impedance corresponds to the resonant frequency (maximum force). The ultrasonic cleaning system operates at a resonant frequency.



Ultrasonic Sensor's impedance curve vs. frequency.gif

Ultrasonic Sensor's impedance curve vs. frequency

Lower the length of the ultrasound electrode- horn to increase the frequency.gif

Lower the length of the ultrasound electrode/horn to increase the frequency

 

Ultrasonic welding machine / mold (factory):

 

Reduce the frequency of ultrasound/speakers:


Steps to reduce the frequency of ultrasound speakers.gif

Steps to reduce the frequency of ultrasound/speakers

Sensor test

 

For proper operation, the frequency and impedance of the sensor must be within tolerance. For example, for a welding system, the frequency should be 2.5% higher than the nominal acoustic setting frequency with a tolerance of +/- 0.25%.

 

The decisive factors for frequency and impedance are the dimensional accuracy of the part, the tightness of the application, the quality of the ceramic and the tuning (similar to the case of ultrasonic propagation).


Using TRZ Analyzer to Determine Transducer Frequency and Impedance.jpg

Using TRZ Analyzer to Determine Transducer Frequency and Impedance


Acoustic test

 

The frequency and impedance of the acoustic group must be within an acceptable range. In welding systems, the tolerance of the frequency is ±0.25%, for example 20khz ± 50Hz.

 

Performance depends on frequency tuning and consistency between components. This can happen when combining sensors and converters (one low frequency and the other high frequency), even when operating at the correct frequency. This type of problem is detected by measuring the impedance.

 

The decisive factors for frequency and impedance are the dimensional accuracy of the part, the tightness of the application, the quality of the ceramic and the tuning (similar to the case of ultrasonic propagation).


Ultrasonic welding acoustic vibration amplitude.gif

Ultrasonic welding acoustic vibration amplitude


Piezoelectric ceramic test

Piezoelectric ceramics are sensor cores and key components. For power applications, the PZT-8 and PZT-4 types are commonly used.

Before reassembling, microcracking of the ceramic must be proven. With the TRZ software, cracks can be easily detected by anomalous peaks in the electrical impedance curve.


Testing Piezoelectric Ceramics with TRZ Softwar.gif

Testing Piezoelectric Ceramics with TRZ Software


Predictive maintenance

 

With predictive maintenance, problems in the ultrasound system can be easily avoided. In general, the frequency deviation represents wear and the impedance represents coupling problems. These problems are solved by refastening and polishing the interface.


Predictive maintenance of systems using TRZ for cutting and welding.jpg


Predictive maintenance of systems using TRZ for cutting and welding

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