ISA-101: Toward a More Effective HMI Strategy

  • March 06, 2015
  • Feature

ISA-101: Toward a More Effective HMI Strategy

An effective HMI should give operators the information they need in a form they can comprehend quickly so they can make good decisions. The new ISA-101 standard helps users understand what those concepts mean and how to implement them.

Byline: Leila Myers and Maurice Wilkins

ISA-101 is in its final stages of becoming a standard. It is designed to develop and establish a consistent approach to effective HMI development and implementation for manufacturing and especially process industries. End users, automation suppliers and system integrators can use this standard to create more effective HMIs, which will lead to higher productivity and a safer operating environment.

Before getting into a discussion of what the standard involves, what are the characteristics of an effective HMI? There is no “perfect” solution for a given situation, but there are common expectations of what an operator should be able to determine quickly by looking at control room screens:

  • Is the process stable, or in an upset situation?
  • Is the plant running where it should be for effective production?
  • Are key process variables currently changing, or stable?
  • How have the most critical variables been running over the past few hours?
  • Are there alarms or upsets? Where are they, what is their source and what should I be doing to fix the problems?

Designers have always tried to provide the best available HMI displays. As technology has moved from panel boards with individual meters, gages and pen recorders to digital control systems with electronic displays—designers have used expanded capabilities to develop new approaches for the benefit of operators and other users.

But some companies began to try and outdo each other by adding more capabilities and “bells and whistles” as new technologies emerged, and some are still doing this today. While these can make for very impressive demonstrations, they don’t always help operators understand the current state of the process, nor do they necessarily help operators make quick well-reasoned decisions in response to abnormal conditions.

From Panel Board to P&ID

Retaining an approach first developed back in panel board days, control system designers typically begin with a detailed P&ID (piping and instrumentation diagram) as the basis of operator displays when creating HMIs. This is very effective if the main objective is showing the instrumentation layout in a process environment, and in some applications it is desirable.

However, if used for basic operator screens, it typically leads to a very congested and confusing picture without sufficient emphasis on the information operators need to perform their tasks efficiently. P&IDs follow the geographical positioning of processes in small chunks, not necessarily the process flow. Consequently, when trying to respond to an abnormal condition, an operator may have to search through multiple screens without ever having an overall picture of the affected processes. 

In most plants, the number of console operators in our post-recession world today has been reduced to the barest minimum. Consequently, those remaining are inundated with information from many sources and need to perform a long list of other functions at the same time. While monitoring the status of the process, the operator may need to communicate with field operators, fill out work orders, check the latest laboratory results, and maybe more. A congested and confusing HMI adds to the stress level and makes quick decisions difficult. It can also lead to errors and unsafe operation.

Figure 1 is an example of a traditional HMI display based on a P&ID. It provides lots of detailed information, but little to identify which items are important. Is the process running well at the moment? Is the plant about to explode? When a pump is shown as red, is it running, shut off or in alarm?

Figure 1: This screen graphic for a distillation tower provides much information, but does not indicate the relative importance of any specific reading. Is the process running just fine, or is the tower about to explode?

Moreover, if a plant considers it important for operators to have a high-fidelity picture of the equipment and instrumentation via HMI screens, it has to commit itself to maintaining such a level of accuracy. Any change in the plant—relocation of a pressure sensor, modification to pump piping, and so forth—needs to be updated on the HMI. However, most sites lack a systematic way to keep displays up-to-date or lack management of change (MOC) procedures to address this problem.

Taking a Lifecycle Approach

Creating and maintaining an effective HMI strategy is a multi-step process, and the entire process can span decades from initial concepts to decommissioning. ISA-101 takes a lifecycle approach to effective HMI management and seeks to identify, define and address different needs across this time span. Figure 2 shows the steps as the standard organizes them.

Figure 2: Creating an effective HMI strategy goes far beyond snazzy screen graphics. The process of looking for ways to improve performance should never stop.

The main HMI lifecycle stages are Design, Implement and Operate. HMI Philosophy, Style Guide and Toolkits provide a set of consistent documentation for HMI management at the site or companywide. Continuous work processes—including MOC, Audit and Validation—can occur throughout the lifecycle.

ISA-101 stresses human factor aspects of engineering and ergonomics in HMI development. Human factors include considerations of sensory and cognitive limits of operators when using the HMIs. Human factor-based displays provide situation awareness for the operator in a consistent manner, without distractions. If operators are less stressed and more focused when performing their tasks, they can work more efficiently with fewer errors.

ISA-101 has been developed by a committee of experienced users, system integrators and automation suppliers over many years through many review and comment cycles. It provides recommendations and best practices for effective HMI systems which will be easy to operate and maintain in the long run.   

End users, automation suppliers and system integrators have embraced a group of HMI management tools and processes proposed by ISA-101. Some sites will want to implement these through internal efforts, and others may want to engage the supplier or integrator.

1. HMI Philosophy Document development: This document explains the principles and goals of HMI management at the site or larger company, and is automation platform independent. It explains how the ISA-101 lifecycle will be implemented, and the roles and responsibilities for individuals involved. Automation suppliers and system integrators advising users while developing this document can draw on experiences of working through HMI implementations across many industries.

2. HMI Style Guide development: This document explains specific aspects of implementing the HMI Philosophy within a specific automation system platform environment. Understanding the mechanics of the automation system platform being used makes sure the implementation is easily maintainable, and ensures the platform’s standard built-in capabilities are used as much as possible. Working with the HMI designer helps ensure all required functionality is provided while system overhead, such as call-up and refresh rates, is minimized.

3. HMI Toolkit development: This library of tools and modules supports easy and consistent HMI display development. Some specific factors should be considered in Toolkit development, including:

a.    Graphics and program code designed as modules supports consistent application and ease of re-use.

b.    Human factors and how they impact size, coloring, contrast, density, symbols, workflow and interaction methods.

c.    Alarm Philosophy requirements for alarm priorities and their presentation in the HMI.

d.    Procedure Philosophy requirements for handling operator interactions with procedures such as startups, grade changes, etc.

e.    Batch user interface requirements.

f.     Location and reproducibility of embedded logic or scripting to support functions embedded in graphics.

g.    Visualization methods to combine lots of numerical data into graphics to allow operators to understand current process status efficiently and recognize abnormalities quickly. Figure 3 is an example of a visualization method for a temperature profile inside a vessel.

Figure 3: Here are two ways of delivering the same information. While the first method is accurate, the second does a much better job of contextualizing the numbers so the operator knows if the process is running correctly at a glance.

4. Cross-functional HMI lifecycle management team development: Members involved in maintaining HMI effectiveness should include operators and all the personnel who have an impact through various lifecycle stages. The team will assist in development of the HMI Philosophy document and will be involved in prototyping, testing and approval of implementations within the system. The automation supplier or system integrator can advise the end user team on the capabilities of the system, and how they can be used to meet requirements. 

5. HMI location and content distribution analysis: Automation suppliers and system integrators can assist end users as they analyze HMI users, locations and types required for the site, including requirements for console design and mobile HMI design. The end user must establish each operator’s realm of control, which has a direct impact on a variety of considerations:

a.    Operator access control based on realm of control and HMI locations.

b.    Alarming and notifications based on realm of control and locations.

c.    Organization of control loops and function blocks based on process hierarchy and access control.

d.    Control logic development for the site based on state-based control philosophy.

6. Operator task analysis: Determining what information needs to be available for a given operator in a given situation depends on understanding what specific users need to accomplish each task including:

a.    Requirements for handling normal and abnormal conditions.

b.    Control elements needed for task performance, such as faceplates.

c.    Supporting information, such as documents, drawings, procedures, etc.

d.    Relationships between tasks.

Figure 4 shows an example of a task-based display.

Figure 4: A task-based display considers what an operator’s specific tasks are and then shows the information necessary to execute those tasks. Critical information is easy to find without sorting through extraneous data.

7. Task and ergonomic design concepts: HMI display designs should be based on task analysis and ergonomics, not on P&IDs. Displays need to provide for execution of detailed tasks as well as an overview of the operator’s realm of control. A display navigational hierarchy should be developed allowing the operator to drill down to greater levels of detail, and there may be one or more displays at each level as required. ISA-101 recommends no more than four levels of hierarchy:

Level 1 – Overview of the operators’ entire realm of control

Level 2 – Overview of one unit operation or a major task

Level 3 – Task detail display, including major control modules

Level 4 – Diagnostic and informational displays

8. Overview display development: Level 1 or Level 2 displays should be based on operator realm of control and KPIs (key performance indicators), not based on P&IDs. Overview displays should provide a concise but informative status of the process. Automation suppliers and system integrators can provide special visualization tools in a range of critical areas:

a.    Current status of critical KPIs, including safety, environmental, production, etc

b.    Recent KPI history

c.    Prediction of performance in the near future

d.    Easy and intuitive navigation to more detailed information when needed

e.    Easy access to alarm information

f.     Status of any procedures in progress

9. Display simulation tool development: As part of the ISA-101 lifecycle model, new and revised HMI displays should be tested prior to being put into operation. A simulation system can greatly improve testing and training activities.

10. MOC process development: Help end users establish a process for managing changes to strategy, displays, graphics, locations, etc. The procedure must include testing and training requirements.

11. Continuous improvement: An HMI should never be considered static. There must be systems for periodic monitoring, for gathering and evaluating user feedback, and for making revisions to optimize HMI displays over time. The procedure must include detailed change logs.

Most of these concepts aren’t new, and many have been applied by progressive end users, automation suppliers and system integrators for some time. The main purpose of ISA-101 is to provide a consistent and repeatable approach any company can use for future implementations.   

About the Authors

Leila Myers is an independent consulting engineer with more than 25 years of experience implementing HMIs for process industries.

Maurice J. Wilkins, PhD, C.Eng, FIChemE, FInstMC, ISA Fellow, is vice president over Yokogawa’s Strategic Technology Marketing Center and is co-chair of the ISA101 standard committee.

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