Human machine interface

The monitoring and control of systems important to safety involves a combination of automatic measurement and control functions, and monitoring and control by human operators. While automatic control and automatic actuation of safety systems are used extensively in modem nuclear power plants, the plant operators remain in overall command of the plant. 

A basic objective should be to achieve a design which is compatible with the strengths and limitations of the human operators. Attention should be paid in the design of the human-machine interface to the duties and responsibilities of the plant personnel, in order to achieve an effective interface between the operating personnel and the plant. This should include paying attention not only to the operators but also to maintainers, inspectors and administrative and emergency personnel at the plant. 

To assist in the establishment of design principles for information display and controls, the operator has dual roles that of a systems manager, including accident management, and that of an equipment operator. 

The Requirements for Design require (Ref. [1], para. 5.54) that the operator, in the role of systems manager, have information that permits  

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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. 

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)... 

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

Human Reliability Analysis (HRA) or Human Error Analysis - A reliability analysis that estimates the potential for human errors to occur due to the work environment, human-machine interfaces, and required operational tasks. 

The central computer is called the master terminal unit, or MTU. The MTU has two main functions to periodically obtain data from RTUs/PLCs and to control remote devices through the operator station. The operator interfaces with the MTU using software called human machine interface (HMI). The remote computer is called the program logic controller (PLC) or remote terminal unit (RTU). The RTU activates a relay (or switch) that turns mechanical equipment on and off. The RTU also collects data from sensors. Sensors perform measurement, and actuators perform control. 

Each of the independent controllers is linked to a human-machine interface (HMI) network. Dedicated HMI operator stations are assigned to each area, with an appropriate number of redundant stations providing backup in case of maintenance or breakdown. A development station permits tooling changes between campaigns to be carried out at the same time as systemiza-tion is carried out on the individual areas. A redundant set of historical data collection stations ensures that all of the data are collected and stored for both regulatory... 

QQ Start-up routine, calibration routine, data transfer/backup, data integrity, power failure, auto lock off, human-machine interface, security access/audit trail, system stress test in event of power failure, alarm tests, operator data entry tests... 

For the purposes of this paper, I will not describe the inference procedures further. I will also say very little about the human-machine interface. However, since expert systems are designed to be built by experts and used by experts and novices alike, the interface is of crucial importance. The examples discussed later illustrate how powerful interfaces are implemented through use of high resolution bit-mapped graphics, menu and "button"... 

More and more commonly, fire alarm panel data is transferred to a safety instrumented system (SIS) for graphic annunciation though the SIS human-machine interface (HMI). 

In the Fish Kill example, the completed analysis of the Human Engineering branch is shown in Figure 9-35. Under the Human-Machine Interface sub-branch, monitoring alertness needs improvement is selected as a valid root cause, and the remaining subcategories have all been discarded. 

The successful design and deployment of any complex system that interacts directly with humans thus calls for socio-technical as well as technical expertise. One particular problem is that of how best to partition an overall task between humans and computers so as (i) to reduce the probability of failures due to misunderstandings across the human-machine interface, and (ii) to make best use of the greatly differing abilities that humans and computers have with respect to following complicated detailed sequences of instructions, and recognizing that a situation is both novel and potentially dangerous. 

The PLC provides more expanded options for control and changes to control. They are provided with many different (I/O) cards such as, digital, analog, device net, modbus, and Internet Protocal (IP). Along with a human machine interface (HMI), the combination makes a solid control system for water treatment. High end PLC RO systems offer pretreatment control, along with multiple external valve option, post-treatment DI, and external pumps. 

An operator interface is used to record data gathered by the PLC.1 The operator interface is usually another computer (sometime called the human-machine interface or HMI). The HMI uses process displays with real-time sensor readings so that the operator can quickly assess the status of the system (see Figure 6.17). The operator uses the control panel to adjust alarm settings and to turn on and off process equipment. Once running, however, the PLC controls and runs the system automatically, without further input from the operator. Common HMI status indicators are listed below ... 

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