A multi processor control system for a gas sensing array

This paper describes a microsystem devoted to air pollution testing and based on metaloxide chemical gas sensors. The system architecture has been conceived by exploiting a modular approach: a central controller is connected via I2C (Inter-IC bus) interface to four ’monosensor’ subsystems (Figure 1) [1,2]. Each ’monosensor’ subsystem detects the concentration of a particular kind of gas and is based on a microcontroller called satellite. The main functions of the satellites are i) to control the sensor operating temperature (Top), by applying a programmable voltage reference (Vref) to a tunable PWM generator, ii) to measure the resistance of the sensitive element, iii) to execute a self-calibration procedure and iv) to communicate the measured values to the controller. The managerial functions of the controller are compliant to the rules of the standard IEEE 1451.2 [3](conceived for transducer-based systems) and implement a Smart Transducer Indipendent Interface (STIM). The STIM communicates with a Network Capable Application Processor (NCAP) by substituting the standard Transducer Independent Interface (TII) with a RS 232 serial interface. The NCAP is implemented on a host PC using a LabView environment. The system has been debugged and tested in suitable environmental chambers. Thanks to the modularity, the system can be expanded including additional monosensor subsystems while keeping the same architecture.