Method and apparatus for simultaneously measuring air contained hydrogen and water vapor concentrations via a single MEMS thermal conductivity sensor

A single MEMS thermal conductivity sensor based system capable of simultaneously measuring an air containing hydrogen and water vapor concentrations which is operated based on:

• hydrogen and water vapor have different temperature coefficients of their thermal conductivities and the sensor is modulated by temperature so as to calculate their concentrations by their contributions to the total thermal conductivity of the air containing hydrogen and water vapor at different modulation temperatures of the sensor and comprises:
• a MEMS thermal conductivity sensor, wherein the sensor created in a silicon substrate and has a chamber recessed in the substrate and covered with a heat insulation membrane,
• a temperature uniformed region in the substrate which surrounds the chamber,
• a heat source on the top of the chamber where a heating resistor is placed,
• a heat sink on the bottom of the chamber and
• a thermopile with its hot junctions placed in the heat source region and its cold junctions placed on the top of the temperature uniformed region where the temperature is the same as the heat sink;
• a microcontroller;
• a nonvolatile memory (ROM) on the microcontroller chip;
• an analog-to-digital converter (ADC) on the microcontroller chip;
• a central processing unit (CPU) on the microcontroller chip;
• a pulse-width modulation (PWM) on the microcontroller chip;
• a voltage follower (unity buffer amplifier);
• a liquid crystal display (LCD);
• a set of heating voltages generated by the PWM, each of them is selectively applied to the heating resistor so as to produce a modulation temperature in the heat source;
• a differential amplifier amplifies the output signal of the sensor;
• the analog-to-digital converter operable to convert the amplified output signal of the sensor into digital values;
• a liquid crystal display (LCD) displaying the output signals of the system;
• a set of air samples each containing known hydrogen concentration (in molar fraction) and known water vapor concentration (in molar fraction);
• and
• a set of air samples each containing unknown hydrogen concentration and unknown water vapor concentration which are required to be measured.