I am trying to measure the "at rest" characteristics of a piezo disc. The piezo is of inexpensive variety, the type enclosed in a black plastic holder: http://www.sunrom.com/img/p/83/83_0_800.jpg
When I use my oscilloscope to measure the piezo, I attach the osc. ground to the piezo black cable, and the 10X selected probe to the piezo red cable. I am able to view the resulting wave at 50mV divisions on my oscilloscope screen.
I find that the piezo "at rest" produces a wave of about 30mV peak to peak, oscillating about 8.3mV. Does this seem like a typical piezo peak-to-peak ambient "output" voltage?
Also, however, there is approximately a 66Hz wave passing through the output signal. What accounts for this 66Hz wave? Is it the 60Hz hum that is somehow created by my oscilloscope, being connected to mains power?