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Tone Burst synchronization

I am sending a 5-cycle tone-burst with central frequency of 60kHz through a simple plate structure (clamped-free). I have 3 PZT sensors: PZT2 sends the tone-burst, located on the left extreme, PZT4 in the middle of the plate and PZT6 on the extreme right.

 

For synchornized generation and acquisition I am using an altered version of the Multi-Function-Synch AI-AO.vi. The signals acquired from the 3 PZTs are correct, with the exception of the initial portion of the signal, where the tone-burst seems to be coincident with the waveforms - see image attached. In other words, for PZT4 and PZT6 it is not expected to see the tone-burst at time 0, it should take at least 0.1 milliseconds to reach PZT4. This means there is some type of initial interferece.

 

I've tried inserting delays on the generated tone-burst and several other options, but this continues to happen. At this point I am not sure if it is a hardware interference or due to the synchronized example code.

 

Any help would be appreciated.

 

Cheers.

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PZT devices are high impedance devices so you may be seeing capacitive coupling in the wiring which is larger than the acoustic coupling through the plate.  Try disconnecting PZT4 and PZT6 and replacing them with capacitors having capacitance similar to the PZT capacitance. The capacitors would be located at the plate end of the cables. Then you would have very similar electrical coupling but no acoustic coupling.  If the coupling is electrical you will see results very similar to what you posted.

 

What happens if you tap the plate with a finger (or screwdriver or hammer, depending on the size) with no electrical excitation?  Do you get the expected delays in the responses of the three transducers?

 

Lynn

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Thanks for the fast response.

 

I've tried taping with a finger when I was continuously generating a sine wave, you could see the alterations on the acquired waveform. I've analyzed the waveforms acquired by each PZT and there is small relation, which would most likely indicate hardware as you suggested. 

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