Trying to understand transformers

[antknee]

I understand transformers as below for example with a step up for volts of 2:

Primary Power = 4W = 2V x 2A

Secondary Power = 4W = 4V x 1A

Now I have the following setup:

Sig gen -> amp -> transformer -> piezo

Now when I use the piezo 'dry' I can put around 150Vpp across it. I put the piezo under water and the same input from the signal generator produces an ugly waveform at 250Vpp or above.

So i'm guessing the water increases the impedance of the piezo?

To get a stable signal across the piezo I now have to lower the output of the signal generator so I'm losing some power?

I think the answer to this is probably easy. Its just I shouldn't be getting up at 5am and then expecting to think much at 11pm!

Thanks.

 

[Hero999]

Not quite, there will be some losses in the transformer.

You're right that the piezo's impedance changes when it's immersed in water and you're right to assume the impedance has increased because the output voltage has increased.

 

[antknee]

I think I am losing some power by now inputing fewer volts into the amp. Probably won't matter much...

I did incidentally measure the losses from the transfomer earlier. I was inputting 0.9Vpp from the sig gen, the amp was outputting 9Vpp into the primary coil and there was 170Vpp across the secondary coil. So about 5% I reckon. It steps up by 20.

Thanks.

 

[erendesh]

I understand transformers as below for example with a step up for volts of 2:

Primary Power = 4W = 2V x 2A

Secondary Power = 4W = 4V x 1A

Now I have the following setup:

Sig gen -> amp -> transformer -> piezo

Now when I use the piezo 'dry' I can put around 150Vpp across it. I put the piezo under water and the same input from the signal generator produces an ugly waveform at 250Vpp or above.

So i'm guessing the water increases the impedance of the piezo?

To get a stable signal across the piezo I now have to lower the output of the signal generator so I'm losing some power?

I think the answer to this is probably easy. Its just I shouldn't be getting up at 5am and then expecting to think much at 11pm!

Thanks.

antknee,
I think you have already answered your quiestion. Piezo are mechanical elements that responds to different physical changes ( like stress, stran) by generating electrcal signal or vice versa. Each Piezo element will have it's own resonating frequency and that will change according to environmental variables.
In water, the freuqnecy that you are applying may be matching or closer to the resonsating frequency of the Piezo element( in water) thus the resonance.
So to reduce the output, either you detune it by changing your input freqency or like you did, apply less voltage across it.

Sandesh

 

[Dragon Tamer]

Aren't piezos a cappacitive device? If so that would explain why it responds diffently under water.

 

[antknee]

Aren't piezos a cappacitive device? If so that would explain why it responds diffently under water.

I'm not sure what this means? Piezo's are capacitive, yes, I think putting them under water would increase the impedance but not affect the capacitance per se?

Thanks.