(22c) Building an Effective Operator Interface for Complex Apc Applications

In order for an operator to consistently use an advanced process control application, he must have a user interface that succinctly shows key information about the state of the plant and of the application. The interface must also provide a means for the operator to drill down and explore specific application behaviors. The more complex the application, the more difficult it is to provide both effective summary information and simple methods for further exploration. Effective presentation of key plant data will improve application service factor and performance.

This paper presents information about operator interfaces for DMCplus and DMCplus Composite systems at ethylene plants within ExxonMobil Chemical. For plants attempting to run as full as possible, operators have a particular interest in understanding what are the current throughput-limiting constraints, so the paper will emphasize the display of appropriate constraint information.

Most ethylene plant DMCplus systems consist of a number of controllers and subcontrollers, too many to watch simultaneously on individual displays. The main "entry portal" for the interface is an overview display. This overview is at a higher level than the traditional DMCplus subcontroller display because it presents information about the plant over the scope of the entire DMC/ Composite system. This is the main display that an operator will use to monitor the plant; it generally eliminates the need for operators to page through multiple subcontroller displays.

The overview display also indicates what section of the plant is currently limiting production. This paper presents a method of identifying the limiting area of the plant by monitoring which DMC subcontroller has more active constraints than unconstrained manipulated variables. This "extra" constraint is the one against which feed is being maximized. If the Composite begins to cut feed, this indication helps the operator quickly deduce the cause and take appropriate action short of turning off the whole application.

The overview also shows when constraints have been given up, which often indicates a need for the operator to take some corrective action. From the overview, the operator can navigate to the correct subcontroller display to find more information about the constraint violation. The operator can also navigate from the overview to a constraint history, or to online documentation.