By Bridget Fitzpatrick, Mustang Engineering
Control systems have changed a great deal over the last 20 years, and control system upgrades are commonplace. Most seasoned automation engineers have been through at least one major upgrade, and the more highly experienced often have battle scars from multiple generations of migrations. But it is only in recent migrations that the human machine interface (HMI) has become recognized as an important role in these projects.
As control systems have become more open and more powerful, the HMI has become more complex with an ever-increasing set of tools to aid the operator. Operators used to be able to see their span of control with a stroll along the panel board or through a handful of process displays.
But as the span of control widens and the numbers of displays grow, the HMI must be redesigned to manage the flow of information and effectively become the funnel through which all available information must pass to reach the operator.
Data Sources and Managing the Funnel
As the control system has advanced over the last twenty years or so, the wealth of information available for delivery to the operator within the control console has grown significantly.
THE HMI PROVIDES DATA TO THE OPERATOR
- Operating Procedures
- Safe Operating Limits
- Daily Orders
- Quslity Information
- Tank Information
- Warehouose Information
- Real-time Sales Orders
- Process Data
- Technology Manual
- Maintenance History
- Lab Information
- Work Orders
- Process Models
- Batch Record
- Operating Log
- Environmental Permit Information
- Blind List
If all this information was continuously displayed, the important information would be lost in the clutter. There is simply too much information to monitor it all. There are technical limits as well and, if the information delivery is poorly engineered, then the HMI can be confusing, slow to respond, and, in worst cases, will fail to respond correctly or at all. But if the information to display is intelligently selected and engineered, the HMI can be a dynamic tool that enables the operator to effectively manage the process through all modes of operation.State Detection and Automated Information Display
Increasingly, systems are designed to automatically manage the information display based on conditions detected in the process or in response to operator interaction. Condition or process state detection is a field with heavy research and development in recent years. Implementing state detection and an HMI that is dynamic based on this state detection needs to be done with caution.
It is important to understand the mental models that operators use to operatore and provide a bridge in the migration from the old view to the new design. Designing that bridge is not always straightforward. I once worked on an HMI upgrade for an application with two process trains, one generally in operation and one in regeneration. The first pass HMI showed mostly only the vessels and equipment for the parts of the process in active use for operation or regeneration respectively, though placed in the same relative position as a reference (a safety review identified what instrumentation needed to be shown in each case, an important consideration in dynamic HMIs).
We had the new and the old HMI running in parallel and the operators refused to use the new HMI. We went back and put in the rest of the process and showed it in a dull color and static manner and the operators started using the new HMI. They noted that they understood the process better having only the important instrumentation shown. We had not originally shown the idled vessels, thinking them a distraction, but they were critical to operator understanding.
Similarly, implementing an HMI that changes significant parts of the interface in response to routine operator mouse-clicks should be undertaken with caution. Most HMI’s automatically change the basic interaction zone (commonly called the change zone or faceplate) as the operator mouse-clicks through the process. Others change the standard trend windows. It is certainly also possible also to change such things as the overview and detail level displays and to provide information on maintenance records, standard operating procedures, environmental permit compliance, related daily orders, and logbook entries to match the subject of the current mouse-click of the operator.
Some level of this can be a very effective tool for the operator, but it all carries an ongoing system loading and a maintenance burden. Ultimately, if you distract the operator from what he or she is trying to control with constantly changing information, then you hinder rather than help operations.
But do not throw out the idea. Certainly, operators must have areas where they can position the current day’s problems and keep them under relatively constant surveillance. This surveillance is an important method of operation and should not be removed. You can help the operator by putting related information in secondary locations, so that it is always there when he or she needs it at a glance and do this to the level that you have space. If the screen space is limited it is better, in my opinion, to provide this related information on a right-click menu and leave the operator to operate, knowing that information is a right-click away.