Performance analysis among different acquisition systems for process control

Data acquisition systems are crucial when implementing control and automation strategies correctly and on time. The knowledge of the sampling time is one of the relevant features to ensure that the sampled data properly represent the process variable. This paper describes the development of a performance index to measure continuously and in real-time the sampling time behavior of typical control and automation systems. To test this index two different architectures are used. The first one uses a data acquisition board plugged directly into the computer bus, and the second one uses a Programmable Logic Controller communicating with a computer through either Industrial Ethernet with OPC or the serial Modbus RTU protocol. In all cases, a custom software application is implemented to calculate the performance index when the sampling time is provided by the Operating System's timer interrupt service. The analysis of the experimental results shows that the proposed performance index can be useful to assess the sampling time behavior or to assist in decision-making about hardware and software choices.