Analogue and digital sensor interfaces for impedance spectroscopy

Impedance spectroscopy is a non-invasive method of sensing electrical material properties. This approach is also suited for sensors transducing non-electrical properties into an electrical impedance. As yet, impedance spectroscopy has only been applicable with laboratory instrumentation, covering a broad frequency and impedance measurement range. By restricting to measurement ranges required by specific applications it is possible to implement the method in sensor interfaces. An interface with substantially analogue circuitry was developed and applied to quartz crystal resonators for sensing density and viscosity of liquids. Additionally, a fully digital interface was realized which is mainly intended for capacitive measurements in liquids. As it samples occurring signals directly and performs a real time sine regression of the acquired probes, it is faster and more precise than the analogue sensor electronics. However, both interfaces have the same precision like laboratory devices for their specified application which is demonstrated with reference measurements.