The success of a PID loop depends upon on the selection, configuration, installation, and maintenance of the field instrumentation and control valves besides the control strategy, PID options and parameters, and controller tuning. The two books shown below being signed at Emerson Exchange are complementary in that taken together they introduce most of the control room and field implementation considerations to provide a more complete picture of the job of the automation engineer.
The following excerpts from Preface of the Essentials of Modern Measurements and Final Control Elements in the Process Industry shows why I wrote the book (besides helping ISA)
This book gave me a chance to get back to my roots as an instrument engineer. I spent the first 7 years of my career in instrument design and construction. After being responsible for the calibration, installation, and commissioning of instruments for a half dozen plants in the 1970s, I became painfully aware that the actual performance of the measurements and control valves was largely unknown. These were the days before the advent of smart instrumentation. We didn’t know the effect of stiction and backlash on valve position or the effect of impulse line, process and ambient conditions on sensors. We didn’t know what was the installed accuracy of measurement or if a valve or measurement had a timely and sensitive response. We shifted set points and just shook our heads when the material and energy balances did not close. Since we were mostly interested in capacity we just pushed on to make more product. Operating efficiency and turndown were not as much an issue, which was fortunate because we didn’t have the spectrum and accuracy of instruments for knowing process performance. The time I spent in the 1980s working on pH, furnace pressure, and compressor surge loops were the ultimate test of sensor and valve sensitivity and speed. My perspective on the importance of the field devices was solidified in the 1990s, when I was part of a corporate wide process control improvement program, most of the opportunities involved tuning loops and adding feedforward control and loops for fed-batch operation. A lot of great ideas went by the “way side” because of missing or imprecise measurements and unresponsive valves.
Today we have smart transmitters and control valves with a rangeability, resolution, and sensitivity that is an order of magnitude better than the typical fare of the last century. A combination of embedded intelligence and new sensor, transmitter, valve, and positioner technology have resulted in dramatic improvements in the window into the process provided by measurements and the way of affecting the process by final elements. Combined with the ability to have additional process variables, diagnostics, and alerts reported to the control room by digital signals and the mobility afforded by wireless communication, we can increase the spectrum and flexibility of the field automation system including finding the optimum locations for process analysis and control. Doors will open for online data analytics, process performance metrics (e.g. energy, quality, and yield) and increased opportunities for basic and advanced control improvements to address the increasing needs of process efficiency, flexibility, and rangeability.
Check out my Oct 1 entry for a book discount and review.