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Human-machine Interfaces: How Best to Represent Your Plant Data Through Real Time Monitoring

Data Intelligence


Digital Advisory

Human-machine Interfaces: How Best to Represent Your Plant Data Through Real Time Monitoring

Ferdinando Borda | Nov 23, 2020

Real time monitoring is the display of plant or system data in real time through tools like web apps available on PCs and mobile devices.

Today more than ever, there is a great demand to be able to access plant data from anywhere: whether from the control room, the office, from home via remote access or even on via mobile while traveling. This tool therefore has a great potential impact on the reality of the industry, as it allows data to be accessed in real time and contributes to meeting performance objectives, reduced consumption costs and product quality control.

The disadvantage of real time monitoring and easy data access, is the common fear that using a monitoring system which can be accessed from multiple platforms will expose sensitive data to attacks that undermine company security. However, such an important competitive advantage should not be discarded for the sake of a risk that can be mitigated and reduced to a minimum, as this one can be by selecting platforms and infrastructure that meet the various industrial cybersecurity standards. 

The first element needed to build a monitoring system in real time will definitely be a system for collecting and recording plant data, a role which is covered by Historian type databases or IoT platforms

But this alone is not enough: when taken out of context, this data often becomes difficult to interpret and use. For this reason a second, indispensable ingredient must be added, that is, a set of graphic displays which efficiently process and present data to users. These displays, called human machine interfaces (HMI), are tools that allow users to actively monitor plant performance.

The issue of data usage is central to real time monitoring systems. Working with poor and confusing graphic representations means the risk of losing a large portion of the power provided by continuous data monitoring.


Human Machine Interface - Implementation guidelines: good design VS bad design


Guidelines for Implementing a Human-Machine Interface

As reported in a study by the Abnormal Situation Management Consortium, poor-performing HMIs are often cited as major contributing factors in serious incidents. Though HMIs have been widespread for some years now, they underwent a profound change following studies on human eye perception and attention span, published by ANSI/ISA-101.01-2015 Human Machine Interfaces for Process Automation Systems. The ISA101 provides criteria for representing process data in a clear, usable, and productive way, with the following advantages:

  • better situational awareness for the operator 
  • increased ability to survey processes 
  • reduced detection and response times for abnormal situations

The guidelines can typically be grouped into five categories: below are the main ones for each category. 



Projecting the display uses context-sensitive methods which bring relevant information into focus. 

This context-sensitive methodology actually reduces the information displayed on the screen at the same time, and therefore acts to reduce the visual clutter. A clean and tidy display lets the user focus on activities that demand their attention without getting distracted by irrelevant data and information.

In the following three images, note how the image on the left does not communicate effectively, as it only gives an indication of the tank’s level in real time. The image in the center is better, as it indicates the threshold values within which the level can acceptably move. The image on the right is even better, as it shows a trend of how the level moves over time. 

Human Machine Interface: effective display (image from “The High Performance HMI Handbook” by Bill Hollifield, Dana Oliver, Ian Nimmo, Eddie Habibi)

Image from “The High Performance HMI Handbook” by Bill Hollifield, Dana Oliver, Ian Nimmo, Eddie Habibi



This set of guidelines aims to speed up and give access to certain actions/screens that require the user’s attention:

  • Set up a navigation scheme between simple and clear displays that allows some steps to be skipped when moving between screens. It needs to be possible to reach the highest levels easily from every level of the display hierarchy, and to be able to navigate to the desired screen with just a few clicks.
  • Providing quick response times while browsing between displays: too slow response time might cause the user to doubt that the system is working properly
  • Using the size of the icons that can be selected, and the distance between these, in a way that allows operators to access the desired area without making mistakes. 



Applying this set of guidelines allows the user’s attention to be focused on the most important points, while avoiding distractions caused by overly complex and colorful graphics and animations.

  • Color intensity must be consistent with the degree of attention required
  • The animation style should focus on critical points in the process, or on safety-related activities. The abuse or inappropriate use of these will decrease their effectiveness
  • Objects and equipment icons must be designed without any unnecessary detail, and the complexity of relationships between equipment must also be minimized 
  • It is therefore not always necessary to display details and supporting information, and it should only be possible on demand
  • Set a color code to make it consistent and unique: the color for alarms will exclusively be used for alarms so as not to create confusion for the operators
  • The color combinations used must be well-contrasted
  • Use a neutral background that maximizes readability without causing eye strain

In the image below, notice how information on the operating status of a pump can mislead the observer. Red, for example, is typically associated with a malfunction, rather than a “not running” status. The image on the right uses neutral colors and is therefore clearer and less confusing.

Human Machine Interface: screen styles and colors (Image from “The High Performance HMI Handbook” by Bill Hollifield, Dana Oliver, Ian Nimmo, Eddie Habibi)

Image from “The High Performance HMI Handbook” by Bill Hollifield, Dana Oliver, Ian Nimmo, Eddie Habibi



On the whole, symbols, lines, texts and numbers have well-defined roles in displays, so it is helpful to consider the following guidelines:  

  • Symbols are used to represent the status of process elements and control objects, while lines and arrows are used to indicate flows of material and control reports. 
  • Use readable text and numbers from the perspective of the habitual operator: the correct use of text and numbers must also relate to the position and distance users are likely to assume when reading the screen. When these are not correctly-sized, you may run into difficulties and misinterpret process data, messages, or even alarms on the screen
  • Codes and abbreviations used must be consistent and clear to the users


Discover how to gain better control over your process using a new high-performance HMI, making the most of international best practices with a package deal tailored to your needs and technology. Contact us


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