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[ Transducer testing method ] |
| The resonance frequency, free capacitance and the dynamic resistance are the most important character parameters of ultrasonic system. The resonance frequency is the most nominal working frequency of the transducer. The generator, booster and mold are required to match with the frequency. The free capacitance means the total capacitance between double sides of the transducer. The component of piezoelectricity ceramic can be looked as an insulator. In fact, the transducer is to work through charging and releasing electricity, so the capacitance decisively effect on the match of generator.
The dynamic resistance can be looked as the wastage degree under ideal condition. In nominal, we believe that smaller the dynamic resistance is much better. However, here’s a basic principle of that:transducer with smaller resistance is uncertainly good, but the transducer with big is surely failed.
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| ２．The testing circuit of constant voltages, as chart.
This method has lower request in equipment is easy to learn on principle. But it’s slow in speed and bad in precision.
The numerical value of the divider resistance Ri is matched with the output impedance of the signal occurrence machine. In general, RT1=RT2, The terminal resistance RT2 value should correspond with transducer dynamic resistance R1, the reference value is 5.1Ω. The distributed capacitance CAB between the A and B is far below the free capacitance CT of transducer. The reactance of the distributed capacitance CT1、CT2 should satisfy: 1/ωCT1>>RT1,1/ωCT2>>RT2.
Regulate the signal occurrence machine frequency make to the terminal resistance designation biggest. The frequency is the series connection resonance frequency fs, which is usually named the frequency of transducer.Note down the designation of the terminal resistance and using the variable resistance to replace the transducer, then adjusting the value to make the terminal electric voltage designation with originally same, at the same time, the value of variable resistance is the dynamic state electric resistance R1.
3. the test of website measuring instrument
More expensive equipment is needed and a computer is also required. It can test automatically with quick speed, high accuracy and completed data. In common, after connection and setting the range of testing frequency, the computer will automatically check up the frequency and find out the frequency of resonance、free capacitance and dynamic resistance. Moreover, it can also show us the anti-resonance frequency, the value of conductance, the equivalent inductance and the mechanical factor of quality (Qm.). |
