C3.2 - Compact Read-Out Electronics for a Micromachined Thermal Conductivity and Diffusivity Sensor

SENSOR+TEST Conferences 2009
2009-05-26 - 2009-05-28
Congress Center Nürnberg
Proceedings SENSOR 2009, Volume I
C3 - Sensor Electronics III
B. Mayrhofer, B. Jakoby - Johannes Kepler University, Linz, Austria, J. Kuntner - Vienna University of Technology, Vienna, Austria
301 - 306


There are several classical methods for measuring the thermal conductivity of liquids One of them is the hot wire method, where a heating wire is embedded in the liquid being sensed. A temperature element beside the heater is used to detect the heat emitted by the heater. Altematively, the heating wire itself may be used as a temperature sensor in the conventional hot wire method, the heater is powered by a DC source and the transient response at the sensor is used to obtain the thermal conductivity of the liquid (or gas).
In our approach, the hot wire method is modified. Firstly, a micromachined sensor element is employed and secondly, a sinusoidal signal is used to power the heater. The sensor thus measures the diffusive heat wave emitted by the heater where the phase and amplitude of the AC-component of the detected signal can be used to detemmine the thermal conductivity and diffusivity (and thus also the specific heat capacity) of the tested liquid. In this paper we discuss suitable read-out electronics, which have been custom-built around the micromachined sensor, where the latter has been fabricated at the institute of Sensor and Actuator Systems of the Vienna University of Technology The previously required amount of measurement equipment facilitating the supply and readout of the sensor was reduced to a single printed circuit board and a PC connected to the board via an USB interface.