### Answer to sTEm–at-Work Puzzle #53: Process Pressure Disturbance (puzzle #52 extended)

The Puzzle: http://flate-mif.blogspot.com/2016/06/stemat-work-puzzle-53-process-pressure.html

Analysis
The tech tested three different sets of control panel settings with their three corresponding pressure versus time graphs shown below. Option 3 was not the Tech's selection nor did Option (2) provide the best results. At this point, the students should appreciate that the analysis of graphic results is not a quick glance process. Although "tuning" process mechanics is a set of simple steps, the skills involved in recognizing that the new settings are correct require a STEM knowledge base. In this puzzle, an appreciation of oscillating behavior is required. At first glance Option 2 might be considered closer to the abscissa value however, the Option 1 response is still oscillating. With more time it will "settle" closer to the set point value. Now there are pivot points in the lesson. This example presented the response to a proportional control algorithm. The main point is clear: a process will not return to set point after a disturbance. Thus a discussion of PI (Proportional Integral) Control is appropriate. It may also be time to introduce the lag concept. This leads to its impact and perhaps "feed forward" control. The instructional path and supporting math and algorithms selections depends on the current knowledge and skills of the students.

Question: The technician selected the setting for the graphic (2) response. Yes or No