C7.4 - Increasing the Dynamic Range of a Digitizing Impedance Analyzer Circuit for Resonating Sensors

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
C7 - Sensor Electronic II
A. Niedermayer, T. Voglhuber-Brunnmaier, J. Sell, B. Jakoby - Johannes Kepler University Linz (Austria)
496 - 501


Resonant sensors are used in a wide range of applications, e.g. as microbalances, chemical sensors in liquid and gaseous environments, and for physical property sensing of liquid and viscoelastic media.
The signals obtained from these sensors are most often afflicted with unwanted or spurious components which, depending on sensor type and operating conditions, can be caused by parasitic sensor effects or by the implemented sensor interface circuit.
The very common way of handling these effects by post-processing the sensor data usually reduces the dynamic range of the measurement interface due to the fact that a certain portion of the input range is occupied by the unwanted signal components.
Especially when using digitizing interface circuits it can be advantageous concerning the utilizable resolution of the system to compensate these parasitic signals before the analog to digital conversion.
In this contribution, a method of analog compensation for parasitic signal components is presented, which is implemented in an largely digital impedance analyzer circuit for resonating sensors.
The interface circuit was primarily dedicated to evaluate the impedance spectra of quartz crystal resonators (QCR) used for viscosity and density measurements of liquids in a zeolite synthesis experiment which is planned to be conducted aboard the International Space Station (ISS).
The implemented signal conditioning concept significantly increases the effective measurement resolution when evaluating strongly damped oscillations of resonating sensors (e.g., QCR operating on higher harmonics in highly viscous media).
Besides QCR, other resonating sensors such as vibrating plates or beam structures with electromagnetic excitation, can be operated with this analyzer circuit.