Confused with figuring out this piezoelectric sensor
A dedicated analog amplifier gives also the power supply. Probably is kind of DC voltage applied to BNC connector, like suppy for old style antenna amplifiers. The signal then, has to have a capacitor to isolate the DC, so you get only AC measurements. These are my tougts , only.

IN the datasheet you will find a power supply of 6mA for dedicated amplifier, and the sensor accepts 8-40mA power supply, don't know how.