Microcontroller-based Data Acquisition Device for Process Control and Monitoring Applications

Process measurement is one of the most important tasks in the whole control system. It is determined by the fact that control accuracy is fully dependent on how preciously measuring chain works. Present-day there is available number of devices performing data acquisition tasks – standard cards for PCI or ISA bus which are suitable for standard personal computers and its industrial versions and modules for industrial automation usually equipped with RS485, CAN and other interfaces. Independent category is formed by smart sensors incorporating sensor, converter to unified signal and data acquisition device in one embedded system with very compact dimensions and low power consumption. They have number of advantageous features such as automatic diagnostic and calibration, high accuracy and immunity against electromagnetic interference due to short signal paths. On the other hand lower operating temperature range reduces their usage to laboratory applications, automotive and aircraft industry where compact dimensions and low weight are crucial. Quite often occurred situations when it is necessary to measure data in terrain where it is not possible to use standard computer equipped with DAQ card. In these cases laptop computer equipped with portable data acquisition device may be very advantageous. On the market are available devices equipped with USB 2.0 connectivity which can fully functionally substitute PCI cards. But they are not able to work without connected computer which must continually control all DAQ operations. Therefore it is not possible to use them in applications where is required long-term monitoring and archiving process quantities in distant areas without access to mains power. This contribution proposes design of multi-channel portable data acquisition device based on low cost general-purpose 8-bit microcontroller Freescale 68HC908GP32, which was developed in our department mainly for control and monitoring educational laboratory models. First part deals with hardware design of the DAQ device with focus on description of operation of individual functional blocks. After that follows description of internal software (firmware) based on real-time operating system RTMON for HC08, which was developed on our department especially for microcontroller-based embedded systems with CPU08 main processor core. Next chapters discuss DAQ device software support in form of program libraries for MS Visual C++, Control Web and Matlab/Simulink development environments, which can significantly improve development time of new process control or