A method implemented at a fault detection and isolation system for indicating loss of integrity of a valve body or actuator legs of a field device (202, 300), the method comprising: transmitting, from the FDI system to the field device (202, 300), a first electrical signal that is representative of first request for a first series of impedance or acoustical measurements and a second electrical signal that is representative of a second request for a second series of impedance or acoustical measurements, wherein transmitting the first request and the second request includes transmitting an indication of at least one of a plurality of frequencies, wherein the first series of impedance or acoustical measurements and the second series of impedance or acoustical measurements are obtained by applying a plurality of electrical signals to the valve body through a piezoelectric sensor (204, 304) at a plurality of frequencies; receiving at the FDI system a first series of impedance or acoustical measurements from the field device; storing the first series of impedance or acoustical measurements; receiving at the FDI system a second series of impedance or acoustical measurements from the field device; storing the second series of impedance or acoustical measurements; comparing, using a principle component analysis module or a multivariate statistical analysis module, the first series of impedance or acoustical measurements and the second series of impedance or acoustical measurements; generating an indication if the first series of impedance or acoustical measurements deviates from the second series of impedance or acoustical measurements, wherein a deviation between the first series of impedance or acoustical measurements from the second series of impedance or acoustical measurements is indicative of a loss of integrity of the valve body or the actuator legs; the method is characterized by: generating a first curve based on the first series of impedance or acoustical measurements and a second curve based on the second series of impedance or acoustical measurements; determining a first plurality of coefficients for the first curve and a second plurality of coefficients for the second curve; and comparing the first plurality of coefficients and the second plurality of coefficients to determine if the first series of impedance or acoustical measurements deviates from the second series of impedance or acoustical measurements. transmitting, from the FDI system to the field device (202, 300), a first electrical signal that is representative of first request for a first series of impedance or acoustical measurements and a second electrical signal that is representative of a second request for a second series of impedance or acoustical measurements, wherein transmitting the first request and the second request includes transmitting an indication of at least one of a plurality of frequencies, wherein the first series of impedance or acoustical measurements and the second series of impedance or acoustical measurements are obtained by applying a plurality of electrical signals to the valve body through a piezoelectric sensor (204, 304) at a plurality of frequencies; receiving at the FDI system a first series of impedance or acoustical measurements from the field device; storing the first series of impedance or acoustical measurements; receiving at the FDI system a second series of impedance or acoustical measurements from the field device; storing the second series of impedance or acoustical measurements; comparing, using a principle component analysis module or a multivariate statistical analysis module, the first series of impedance or acoustical measurements and the second series of impedance or acoustical measurements; generating an indication if the first series of impedance or acoustical measurements deviates from the second series of impedance or acoustical measurements, wherein a deviation between the first series of impedance or acoustical measurements from the second series of impedance or acoustical measurements is indicative of a loss of integrity of the valve body or the actuator legs; the method is characterized by: generating a first curve based on the first series of impedance or acoustical measurements and a second curve based on the second series of impedance or acoustical measurements; determining a first plurality of coefficients for the first curve and a second plurality of coefficients for the second curve; and comparing the first plurality of coefficients and the second plurality of coefficients to determine if the first series of impedance or acoustical measurements deviates from the second series of impedance or acoustical measurements. generating a first curve based on the first series of impedance or acoustical measurements and a second curve based on the second series of impedance or acoustical measurements; determining a first plurality of coefficients for the first curve and a second plurality of coefficients for the second curve; and comparing the first plurality of coefficients and the second plurality of coefficients to determine if the first series of impedance or acoustical measurements deviates from the second series of impedance or acoustical measurements.