How to test terminals on a capacitor/pzt for + or -

[antknee]

I have some pzt, it acts much like a capacitor. The pzt is marked on one side with a red dot. I'm sure this means it is either the positive or negative terminal. How would I test which is which? Is there much difference?

Thanks.

 

[Hero999]

Assuming you're talking about a piezo transducer.

It's like any other speaker, there's no true positive or negative but phase and anti-phase, in short it doesn't matter unless you're driving more than one.

For piezo discs, I normally connect the copper to the 0V rail and the foil to the output of the driver but that's only because it isn't always convenient to have the metal plate floating at a higher voltage than 0V.

 

[antknee]

Hi Hero,

I meant just plain pzt discs and rings. I've included a picture, it is essentially a piece of pzt that has been cut into disc. I've soldered on some terminals to test its capacitance and resonant frequency. You can see the red dot just above the solder. I can't find any difference between the terminals as you mentioned. As i'll be using just the one I guess its not something I need to think about.

Cheers.

Antknee.

 

[antknee]

The discs and rings I have don't have a copper terminal although I have seen them. These just seem to have a white scratchy metal, perhaps this is the foil you are mentioning, i'm not sure how I'd describe it!

Edit: I think by foil you mean on a transducer it must have a means of keeping in particular water off the pzt. I'm still not particularly sure what to call the white material on this pzt, it scratches off easily and must be a conductor.

 

[Hero999]

The white scratchy material is the foil electrode I was talking about.

As I said above, the polarity isn't important, unless you're driving more than one, in which case you just need to make sure that they're all connected up the same way.

 

[antknee]

Ah I see. Now I know what to call it.

Cheers.

Antknee.