A field device comprising: a piezoelectric transducer having a first terminal and a second terminal; normal mode circuitry adapted to operate the piezoelectric transducer during a normal operation mode; and self-test circuitry adapted to supply a charging current (Ic) to the piezoelectric transducer during a diagnostic self-test mode and providing a test signal as a function of voltage on the piezoelectric transducer as a result of the charging current (Ic), wherein the self-test circuitry includes: a resistor adapted to supply the charging current (Ic) through the resistor to the first terminal of the piezoelectric transducer; characterised in that it further comprises switching circuitry (30, 32, 36) adapted to connect the resistor to the first terminal of the piezoelectric transducer, and to connect the second terminal to ground during the diagnostic self-test mode, wherein, during the diagnostic self-test mode, the self-test circuitry samples the voltage on piezoelectric transducer within a predetermined time period after the charging current is supplied to the piezoelectric transducer, wherein, if the voltage on the piezoelectric transducer exhibits a RC charging curve representative of a normal capacitance indicated by the sampled voltage being between a first threshold value and a second threshold value, then the self-test circuitry provides a test signal that indicates a normal condition. a piezoelectric transducer having a first terminal and a second terminal; normal mode circuitry adapted to operate the piezoelectric transducer during a normal operation mode; and self-test circuitry adapted to supply a charging current (Ic) to the piezoelectric transducer during a diagnostic self-test mode and providing a test signal as a function of voltage on the piezoelectric transducer as a result of the charging current (Ic), wherein the self-test circuitry includes: a resistor adapted to supply the charging current (Ic) through the resistor to the first terminal of the piezoelectric transducer; characterised in that it further comprises switching circuitry (30, 32, 36) adapted to connect the resistor to the first terminal of the piezoelectric transducer, and to connect the second terminal to ground during the diagnostic self-test mode, wherein, during the diagnostic self-test mode, the self-test circuitry samples the voltage on piezoelectric transducer within a predetermined time period after the charging current is supplied to the piezoelectric transducer, wherein, if the voltage on the piezoelectric transducer exhibits a RC charging curve representative of a normal capacitance indicated by the sampled voltage being between a first threshold value and a second threshold value, then the self-test circuitry provides a test signal that indicates a normal condition. a resistor adapted to supply the charging current (Ic) through the resistor to the first terminal of the piezoelectric transducer; characterised in that it further comprises switching circuitry (30, 32, 36) adapted to connect the resistor to the first terminal of the piezoelectric transducer, and to connect the second terminal to ground during the diagnostic self-test mode, wherein, during the diagnostic self-test mode, the self-test circuitry samples the voltage on piezoelectric transducer within a predetermined time period after the charging current is supplied to the piezoelectric transducer, wherein, if the voltage on the piezoelectric transducer exhibits a RC charging curve representative of a normal capacitance indicated by the sampled voltage being between a first threshold value and a second threshold value, then the self-test circuitry provides a test signal that indicates a normal condition.