Thermal conductivity sensor

DESCRIPTION：

    The sensor element consists of a silicon chip with a thin membrane approximately 1mm² in size of a material with extremely good electrical and thermal insulating properties. On the membrane are two thin film resistors (R_m1, R_m2) which are both used for heating the membrane and for measurement of membrane temperature Tm.

    The resistors are passivated to protect them from the effects of the gas. The membrane is completely covered by a second small silicon chip with a rectangular cavity etched in. The hollow space thus formed above the membrane is the thermal conductivity section. The gas comes to the measuring section through a small lateral opening in the membrane cover by diffusion only, and not by flow.

    The sensor chip and its cover are attached to a silicon support which also permits gas exchange to the lower side of the membrane. The sensor is electrically connected to an eight pin base by gold wire bonding.

    Due to the thermal conductivity l of the gas surrounding the membrane, thermal energy is dissipated from the membrane held at higher temperature Tm. Measured is the signal needed in a temperature stabilization circuit to keep the excess temperature of the membrane DT constant.

    On the solid part of the chip are two more resistors (R_t1, R_t2) to measure and compensate for the effect of the ambient temperatur.

FEATURES：

• Measuring hydrogen content thermal conductivity

• Analyzing binary gas by evaluating

• Determination of CO2 vs. Methane

• Discrimination of natural gas

• Measurement of Helium or Xenon contents

APPLICATIONS：

• Industrial application

• Monitoring of gas characteristic

• Determining gas concentration

• Landfill or digestor gas

• Different origin gas or compositions gas

ABSOLUTE MAXIMUM RATINGS：

SPECIFICATION：

Base material：Silicon, microstructured by anisotropic etching

Mechanical stress tests have been performed on prototype sample devices for：

Vibration：in accordance with IEC 68-2-6 Appendix B (1982) 10 cycles;