Performance Analysis of Industrial Communications Devices and their Associated Protocols

How much faster is PROFIBUS than Modbus? What are the performance characteristics of one over the other? Many of the common communications devices and protocols used for industrial systems do not have quantitative measurements or comparisons published in the public domain. These protocols are commonly used in real-time control systems and process control systems using Programmable Logic Controllers (PLCs) as part of the collection of information from remote devices. Many of these devices can vary from proximity sensors and limit switches to bar code scanners and other PLCs. One of the most important attributes that these systems require is called determinism. The definition for determinism from the Merriam-Webster dictionary [1] is: 1 a: a theory or doctrine that acts of the will, occurrences in nature, or social or psychological phenomena are causally determined by preceding events or natural laws b : a belief in predestination 2 : the quality or state of being determined For many engineers, this means that the equipment they design will have predicable responses and results from the PLCs and other types of controllers used for industrial equipment and systems. System engineers and developers of industrial and military equipment generally do not, but should, perform this type of analysis for their equipment. Most of the common comparisons are only based on the bandwidth of the transport media, such as 10 Megabit Ethernet or 100 Megabit Ethernet. These comparisons do not take the protocols or the volume of data into consideration. Most system engineers and developers select devices and protocols based on simply the raw bandwidth of the media, rather than taking the overhead of the protocols and hardware latencies into consideration..

Determination of cardiac output using ensemble-averaged impedance cardiograms

Although impedance cardiography provides safe and reliable noninvasive estimates of stroke volume in humans, its usefulness is limited by the necessity for subjects to be apneic and motionless. In an effort to circumvent this restriction we studied the validity of ensemble-averaging of impedance data in exercising normal subjects and in intensive-care patients. The correlation coefficient (r value) between 128 ensemble-averaged and standard hand-digitized determinations of stroke volume index from the same records taken during rest and exercise in six normal male subjects was +0.97 (P less than 0.001). The r value for ensemble-averaged stroke volume indices during free breathing and breath hold in the same subjects was +0.92 (P less than 0.001), suggesting that breath hold did not significantly affect the stroke volume estimation. In 14 freely breathing hospital intensive-care patients the r value between simultaneous thermodilution cardiac output readings and ensemble-averaged impedance determinations was +0.87 (P less than 0.01). The results indicate that ensemble-averaging of transthoracic impedance data provides waveforms from which reliable estimates of cardiac output can be made during normal respiration in healthy human subjects at rest and exercise and in critically ill patients. </jats:p