Study And Development Of Multi-functional Data Acquisition Instrument

Data acquisition is one of the key sectors in modern measurement and control system. The data acquisition systems are usually designed for particular desire, their each channel only collect single kind of signals, thus their features are single and universality is not strong. Based on this issue, for the purpose of the pressure, flow, liquid level, displacement, frequency, temperature, pulse signals, switch signals data acquisition desire for industrial environment, synthesized the merits of PLC and paperless recording instrument, high performance, general-purpose and portable data acquisition instruments with multi-channels were fabricated. They can achieve multi-functional data acquisition on each analog input channel, and at the greatest extent to meet the multi-channel, high precision data collection desire of many kinds of industrial use.The whole system contains a data acquisition board served as lower computer to achieve the mission of dada collection and a upper computer supervisory interface to accomplish the display of data which is from the lower computer on laptop/PC, and they communicate with each other through RS232/RS485 bus with Universal Serial Interface Protocol (USS Protocol).The board based on ADμC834 with 24-bit∑-△ADC embedded accomplishes the channel selection and function selection by two stages analog switches, which is collaborated with the program with C language to accomplish the functions of data collect of analog and digital signal, data send, the control and output of digital signal, the analysis of noise, and so on.The upper computer supervisory interface is developed by C#.net language and SQL Server 2005 database, its requirements and user case modules are analyzed, and its design produces of experiment setting module, operation and display module, requirement module, noise analysis module, filter algorithm are introduced in detail.The functions and performance of hardware and software of this system are tested; noise analysis is done to verify its precision. The experimental results show that the systems have powerful functions, high accuracy, satisfying real-time. The acquisition instrument provides 8-channel analog input and 12-channel digital input and 8-channel digital output with full-isolated, and each analog input channel can achieve the signal collections of standard voltage, standard current, thermocouple, resistance/thermistor, 3-Wired/4–Wired RTD signal collection. When the collecting mission is changed, just need to set the corresponding collection command again. The real-time results of data collection can be displayed on laptop/PC in the form of graph and table, and possess the noise analysis function, accurate measurement function. For the real-time measurement, when Pt100 is used for temperature measurement, its precision reaches±0.2℃, its uncertainty degree is less than 0.03℃; when thermocouple is used for temperature measurement, its precision reaches±0.5℃, its uncertainty degree is less than 0.08℃; when voltage/current signal is used, its precision and uncertainty degree are less than 0.3%; when resistance/thermistor signal is used, its precision and uncertainty degree are less than 5%. Accurate measurement has higher precision and lower uncertainty.The system has features of low cost, high precision, delicate and exquisite, strong anti-interference and universality, and has broad market prospects. The acquisition instruments have been used in actual industrial field with satisfactory results.