Hi all,

I have been trying to create a circuit to measure the voltage through a piezo buzzer but am struggling to understand what is going on with this system so I will describe what is happening.

I have a 27mm DI Piezo disc that is being fed with a square wave signal, at the negative end of the piezo I have a 0.1-ohm resistor as a shunt and an op-amp (AD820) connected after the piezo and before the shunt as seen in the image below.

The top graph image is the signal from the signal generator and the bottom signal is from the op-amp, this is the closest I have gotten to a tangible signal from the piezo however it now looks as if the signal has been differentiated at some point. I am assuming that I should be getting a square wave out of the op-amp but am unsure as to what has happened.

Note that the op-amp is powered by a +/-10v power supply and has capacitors alongside the inputs.

Ultimately I am trying to measure the instantaneous power draw and the time average power so that I can create a few types of piezo actuators and this will be part of the selection process as we are looking for good performance and low energy needs.

 

It looks like you are using a PC scope which is AC coupled.

 

it now looks as if the signal has been differentiated at some point

It has. A piezo crystal behaves as a capacitor.
Welcome to AAC!

 

It looks like you are using a PC scope which is AC coupled.

I am using a daq and lab view, thank you for your help

 

It has. A piezo crystal behaves as a capacitor.
Welcome to AAC!

I did think this was going to be the case, I am going to be having a chat with my electronics tech at some point this week to try and work this out. I have also done a quick integrator on this signal but with no luck. And even a diode over the piezo as at first I did think this was inductive.

Electrical is not my strong point and the more I learn I realise this more so each day. Thank you for your time.

 

Tell us the make and model of the DAQ.

 

Tell us the make and model of the DAQ.

NI-DAQ USB6008

 

Hi Living
Datasheet posted.
E

 

OK, as far as I can tell, bandwidth is 0-5kHz.

 

OK, as far as I can tell, bandwidth is 0-5kHz.

I have been applying a 10 hz to 3khz Square wave so this should be within this window right?

 

The reason why you are getting those results is because of the electrical and physical properties of a piezo-electric device. When a step voltage is applied to it, it physically deforms, which takes a finite time. As it deforms, a small amount of current flows to charge it and it generates a back-emf equal to the applied voltage. When the applied voltage returns to zero, the opposite occurs.

 

The reason why you are getting those results is because of the electrical and physical properties of a piezo-electric device. When a step voltage is applied to it, it physically deforms, which takes a finite time. As it deforms, a small amount of current flows to charge it and it generates a back-emf equal and opposite to the applied voltage. When the applied voltage returns to zero, the opposite occurs.

Dose this mean that I am able to do somthing to repair the signal or is this actually what I need to calculate the instantaneous power and time average power?

 

Dose this mean that I am able to do somthing to repair the signal or is this actually what I need to calculate the instantaneous power and time average power?

No, this is a brief description to help you to understand what happens when you apply a step voltage to a piezo-electric device. Use the knowledge in any way you wish.

 

No, this is a brief description to help you to understand what happens when you apply a step voltage to a piezo-electric device. Use the knowledge in any way you wish.

Thank you for the help I will update as progress happens

 

A piezo transducer produces no low frequencies.
A squarewave needs frequencies down to and including DC.
Here is the frequency response of a typical piezo transducer: