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Feb
19

Display content – part 2

A mistake often made with operator displays is to limit the scope of the design work to mimic the process equipment shown on P&IDs and Process Flow Diagrams (PFDs). These initial displays include measurements, valves and final control elements. They include enough of the process equipment and piping so that the process flow can be followed. Display navigation is added, allowing the operators to quickly follow the flow of the process and drill into and out of detail as required. Over time additional related information from upstream and downstream processes is often added to the displays. The overall effectiveness of the system of displays depends greatly on the experience of the designers, the involvement of the operators and the manner in which the graphic displays are structured.

ANSI/ISA-101.01-2015, Human Machine Interfaces for Process Automation Systems takes a different approach. ISA101 covers the philosophy, design, implementation, operation, and maintenance of HMIs for process automation systems, including multiple work processes throughout the HMI life cycle. It defines the terminology and models to develop an HMI and the work processes recommended to effectively maintain the HMI throughout its life cycle. It also provides a description for Level 1, 2, and 3 displays. It does not drill into how the content supported on each of these display levels is determined.

So how is the content for Level 1 and Level 2 displays identified? There are a number of techniques including decision mapping, storyboarding, and storytelling. These techniques have been largely developed in other industries and are being adopted in our industry. These techniques can also be used for advanced control applications and data analytics. They are also work well for identifying content for mobile applications. I will be returning to these related topics in future blogs.

The material used in this blog was largely investigated as part of several projects at the Center for Operator Performance (COP).

Decision Mapping

Decision mapping is a systematic review and characterization of the decisions made by operators and users of the system. As part of this technique a rating and clustering technique is used to map the available information to decisions. Parameters are allocated to displays based on their relation to the decisions.

The first step with this approach is to identify the key decisions for each major section of the process. As an example, for a hydrocracking unit key decisions such as “Why have I lost hydrogen?” and “Why are my separator levels changing?” are considered. Some decisions, for example, “Have I lost hydrogen?” requires only checking hydrogen measurement and should be alarmed. On the other hand, “Why have I lost hydrogen?” requires the analysis of multiple data points. In the COP study test case the following decisions were selected for a typical hydrocracking unit:

  • Why have I lost hydrogen?
  • Why am I venting so much?
  • Why has the recycle gas changed?
  • Am I maximizing preheat?
  •  Am I operating inefficiently?
  • Can I increase charge
  • Is my feed system set up to produce desired product?
  • Is my recycle Compressor operating near optimum?
  • Am I at risk for a temp runaway?
  • Why has the reactor temp taken off?
  • Why don’t I have enough feed?
  • Are my reactors setup to produce desired product?
  • Why am I not making the desired amount of light product?
  • Why is the naphtha off spec?
  • Why are my separator levels changing?
  • This should be displayed all of the time (cross check)

Determining which parameters are best for supporting these decisions is the next step. Since a hydrocracker can have 3,000 or more tags, selecting all of them is not practical. The procedure starts by dividing the unit into logical sections and then defining key data elements based on the process requirements and items that have important alarms and similar factors.

In many cases the data points may be combined to provide information that will aid the decision-making process. In this example, the number of tags was reduced from 3,000 to 120, with a total of 194 data elements. Some examples are shown below.

  • FRONT END High press separator pressure PV
  • BACK END Splitter Top press Output
  • BACK END Splitter Fuel Gas Pressure PV
  • UTILITIES Wash water flow PV
  • BACK END Splitter Top press PV
  • FRONT END Make-up compressor Unit press Mode
  • FRONT END Make-up compressor Unit press Output
  • FRONT END High press separator pressure Output
  • FRONT END Charge Unit Charge flow PV
  • FRONT END Furnace/heater (both HT/HC RXs) Fuel Gas Pressure PV

The next step is determining which among these data points are the most important for each decision. In the COP study, experienced operators were asked to rate the importance of key data elements relative to each decision. The operators rated each data point on a scale of 0 to 5.

5 – Critical or extremely important
4 – Very Important
3 – Important
2 – Somewhat important
1 – Not at all important
0 – Doesn’t exist on my unit

The responses from the operators were combined and analyzed. The results of the survey were evaluated using a technique called cluster analysis to determine how the parameters should be organized. The parameter ratings were then used to select the top parameters for each cluster.

Storyboarding

Storyboarding is an effective way to flesh out user requirements and behaviors. By employing a facilitator, teams can work together to capture key ideas and information and document them on Post-it pads or cards. These pieces of information can be organized into related. Storyboards provide a framework to help participants be specific about relating experiences, including expectations, decisions and observations, rather than just vague commentary.

Storyboarding sessions are made up of key stakeholders including leading operators, engineers, and shift supervisors. This approach works well because it allows the participants to express their ideas through scenarios and stories that they can all relate to. Storyboards are a good way to keep emotions out of verbal communication while at the same time capturing key aspects of the story on paper (everyone should feel comfortable in contributing). Here are three things to consider:

1- Be clear about the purpose. Like all workshop activities, it’s important that you know exactly why you’re conducting the storyboarding activity. You may end up with a range of interesting storyboards, but without a clear goal, they may not give you the insights you’re hoping to derive.

2- Materials for the storyboard session. A large surface to capture information on (e.g. a large whiteboard) and pens, pencils, and colored Post-it pads.

3- Facilitation. At the start of the meeting the facilitator provides a simple one-page instruction sheet about what it is you want your participants to do. To get things started the facilitator sets the scene by selecting the equipment the session will start on and then getting participants to describe experiences they have had. What kinds of things went wrong? When did you observe something? When did it start? What did you do? Capture the experiences step-by-step, including anything that went well or went wrong. Ultimately you are trying to tease out relationships, key parameters, and leading indicators. Along the way capture the information on your storyboard. Depending on how things are progressing you may want each of the participants to draw their own storyboards, or if they will work in small groups, use the groups and compare storyboards. Only allow about ten minutes to let them think and draw.

Get everyone to focus on the same sorts of elements. Get them to think about triggers (what has happened to start this story in the first place), the single goal that we want to achieve, and what the final outcome is. Should it show a clear benefit of a solution? Or an existing problem?

Storytelling

Storytelling is another method used to flesh out requirements. This method stresses the importance of intuition, following your hunch, and trusting your years of experience to lead you in the right direction. Intuition, in and of itself, is extremely undervalued. Why? Because it’s fallible. It’s only a first step; it needs to be checked by analysis. The storytelling method is well described by Gary Klein.

Dr. Gary Klein, “Sources of Power: How People Make Decisions Paperback”, The MIT Press, February 1999