HMI Design: An Analysis of a Good Display for Seamless Integration between User Understanding and Automatic Controls

In process automation industry operator interface is usually a Human Machine Interface Unit (HMI). HMI plays a significant role in creating a friendly visual environment between the user and the technology. It is considered to be the window to the automation control system. Controlling through finger touch has replaced the use of hammers and manual switches enormously. With the increasing application of HMIs in industry, a good number of software tools are being introduced and the competiveness in designing HMI displays is increasing tremendously. This paper focuses on various important aspects in designing HMI displays to meet the quality criteria such as ease and seamlessness in user understanding, efficiency of learning the HMI design software tools and satisfaction of the operators to control large systems. These aspects consist of issues with screen layout, color representation, graphics and pictures, text and data values, alarms, navigation, control and so on. The scope of this paper is to gain knowledge about how to incorporate as much information in one limited display monitor, by multiple numbers of pages in a graphical hierarchy. This is needed to provide an operator with clear visual understandings of process operations with both moderate and complex applications. This paper also consists of appropriate guidelines for designing an HMI unit in a most efficient way. As examples we designed an HMI unit intended to control a packaging machine coupled with Allen-Bradley CompactLogix and MicroLogix Programmable Logic Controllers (PLC) systems. Introduction: Major portion of the operations in modern manufacturing industries are performed by the implementation of automation technology. In order to achieve high productivity from the automated machineries used in the industries at present, the technology is growing more complex, making issues of end-product equipment safety, ease of operation and reducing human error extremely significant. As a result the interaction between human operators and automated machines are becoming more critical. Human machine interfaces (HMIs), enable the operators for complicated machineries to see, touch and control high stress industrial processes through touch screen displays. As HMI systems are turning to be the principal point of interaction between the user and the machine/process in automation industry, a good HMI display makes this interaction flawless and smooth. On the contrary, a poor HMI design makes it difficult for the operators to have a clear understanding of the machine/process and contributes to reduced systems performance, significant amount of production loss, or even accidents/fatalities at worst. In the process industry, high performance HMI display design focuses on providing maximum amount of effective information related with a machine/process. There is a misconception that incorporating more raw data means providing more information. In real sense, providing useful data with proper presentation is reflected as information while designing an efficient HMI display. Well-designed HMIs result to visually better system understanding and easy troubleshooting for the operators. Unfortunately, many design engineers do not emphasize on practicing industrial standards while designing HMI displays for controlling complex machineries. Most of the designers have the tendency to design screens with bright colors and complicated graphics (e.g. flashing animated flames, 3D process vessels, spinning pumps/ moving conveyers etc). These kinds of displays make it difficult for the operators to be able to visually understand the overall operational conditions of the process. Not following the specified industrial color codes may result to confusions or misinterpretations of control commands which increase the probability of human errors and may even cause system breakdown/production loss. As the market is becoming intensively competitive, all of the above aspects along with some other important factors such as, graphical hierarchy in multiple page display, proper system alarm status etc, are critical for designing a operator friendly and efficient HMI unit design.