Human-Machine

The process control functions and the operator interface, also referred to as man-machine interface (MMI) or human-machine interface (HMI), is provided by separate nodes. This approach is referred to as split-architecture, and it permits considerable flexibihty in choosing a configuration that most appropriately meets the needs of the application. 

The first component of the systems approach to error reduction is the optimization of human performance by designing the system to support human strengths and minimize the effects of human limitations. The hiunan factors engineering and ergonomics (HFE/E) approach described in Section 2.7 of Chapter 2 indicates some of the techniques available. Design data from the human factors literature for areas such as equipment, procedures, and the human-machine interface are available to support the designer in the optimization process. In addition the analytical techniques described in Chapter 4 (e.g., task analysis) can be used in the development of the design. 

The first set of case studies illustrates errors due to the inadequate design of the human-machine interface (HMI). The HMI is the boundary across which information is transmitted between the process and the plant worker. In the context of process control, the HMI may consist of analog displays such as chart records and dials, or modem video display unit (VDU) based control systems. Besides display elements, the HMI also includes controls such as buttons and switches, or devices such as trackballs in the case of computer controlled systems. The concept of the HMI can also be extended to include all means of conveying information to the worker, including the labeling of control equipment components and chemical containers. Further discussion regarding the HMI is provided in Chapter 2. This section contains examples of deficiencies in the display of process information, in various forms of labeling, and the use of inappropriate instrumentation scales. 

This section illustrates some of the more global influences at the organizational level which create the preconditions for error. Inadequate policies in areas such as the design of the human-machine interface, procedures, training, and the organization of work will also have contributed implicitly to many of the other human errors considered in this chapter. 

Design of the human-machine interface (HMI) such as control panels to ensure that process information can be readily accessed and interpreted and that appropriate control actions can be made... 

The practical needs of military and aerospace systems tended to focus interest on human-machine interfaces (e.g., aircraft cockpits), with particular emphasis on information displays and the design of controls to minimize error. The predominant model of the human prevalent at that time (called behaviorism) concentrated exclusively on the inputs and outputs to an individual and ignored any consideration of thinking processes, volition, and other... 

From the traditional HF/E perspective, error is seen as a consequence of a mismatch between the demands of a task and the physical and mental capabilities of an individual or an operating team. An extended version of this perspective was described in Chapter 1, Section 1.7. The basic approach of HF/E is to reduce the likelihood of error by the application of design principles and standards to match human capabilities and task demands. These encompass the physical environment (e.g., heat, lighting, vibration), and the design of the workplace together with display and control elements of the human-machine interface. Examples of the approach are given in Wilson and Corlett (1990) and Salvendy (1987). 

The human-machine interface (usually abbreviated to interface) is a major focus of interest for the HF/E approach to the reduction of human error. A representation of the interface in a CPI context is provided in Figure 2.2. The interface is the boimdary across which information from the process is transduced by sensors and then displayed in a form that can be utilized by the... 

In the CPI, the most extensively studied human-machine interface is in the central control room in automated plants where plant information is displayed on visual display units (VDUs) and appropriate control actions are made by the operating team. In the case of a highly automated plant, the primary role of the human is to respond to unexpected contingencies such as plant states that have not been anticipated by the designers of the automatic... 

FIGURE 2.2. The Human-Machine Interface (adapted from Wickens, 1984). 

The term control panel refers to the instrumentation console in a central control room through which process information is communicated to the process worker and via which the worker changes the state of the process. This category includes display elements such as chart recorders, bar indicators, dials, and modem VDU-based systems together with control elements such as buttons, switches, track balls and mice. The control panel is the human-machine interface (see Chapter 2) that has traditionally received the most attention from human factors specialists. 

They can be used for designing the human-machine interface. 

The TA methods described so far can be evaluated in terms of their focus on different aspects of the human-machine interaction. To facilitate the process of selection of appropriate TA methods for particular applications. Figure 4.14 describes ten criteria for evaluation. These criteria are in terms of the usability of the methods for the following applications ... 

In general, HTA, IMAS, and CADET fulfill most of the above criteria, hence they can be used together as a framework for carrying out both action and cognitive task analysis. When particular aspects of the human-machine interaction must be examined in greater detail for example, the temporal characteristics of the task or the team communications, certain methods can be selected to provide this information—OSDs in this case. Most TA methods... 

Although checklists are a useful way of transferring information about human-machine interaction to designers and engineers, they are not a standalone tool and they cannot provide a substitute for a systematic design process. The main concern with checklists is that they do not offer any guidance about the relative importance of various items that do not comply with the recommendations, and the likely consequences of a failure due to a noncompliance. To overcome such problems, checklists should be used in combination with other methods of task analysis or error analysis that can identify the complexities of a task, the relationships among various job components, and the required skills to perform the task. 

Adequacy of human-machine interface or task design... 

E. Human-machine interface E. Supervision during work... 

Root causes 4 and 5. Human-machine interface less than adequate. The labeling of the pipe was poor and confusing, the general ergonomics of the work situation was poor. 

On both platforms the ergonomics of layout and instrumentation would hinder rapid and effective response to a significant fire or gas release. The overall ergonomics in both control rooms betrayed the lack of a coherent human-machine interface design philosophy being implemented within the design process. 

Design of human-machine interfaces (e.g., process information displays, alarm systems, plant labeling)... 

Rasmussen, J. (1986). Information Processing and Human-Machine Interaction. Amsterdam North Holland. 

Human-Machine Interface The boundary across which information is transmitted between the process and the worker, for example, analog displays, VDUs. 

Risk Homeostasis The theory that an operator will attempt to maintain a stable perception of risk following the implementation of new technology that increases the safety of a human-machine system. The theory predicts that operators will take greater risks where more safety devices are incorporated into the system. 

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