# Cognitive Principles for Remote Condition Monitoring Applied to a Rail Pantograph System
## 4 Demonstration HMI Design  
Having defined the overall conceptual architecture, the next stage was to design the more detailed elements of each display. There are many guidelines and standards available to one designing a user interface [39, 40]. These contain specific tips and features for a designer or developer to implement into their designs. One key concept that frequently appears in the literature to achieve an easy-to-navigate and aesthetically pleasing interface is to only include visual elements that are absolutely essential, avoiding the display of irrelevant information and utilising progressive disclosure (hiding information until it is useful) when necessary [11].  
Another key concept is to make the system state clearly visible: ensuring the system accurately represents what is happening in the sensed environment, and keeping the user informed, before and after, of the effects their decisions have. The next concept to keep in mind whilst designing is to make sure that the user feels like they are the one controlling the system, rather than feeling like the system controls them. This involves allowing users to navigate the system whichever way feels natural to them, i.e., allow them to use either the mouse, keyboard, or touchscreen to select an option, then use a different method to select the next option, providing them with multiple routes to achieve a goal. This also involves clearly indicating where the user is in the overall conceptual architecture, and ensuring where possible that every decision the user makes is reversible. Whilst using these concepts, it is important to remember that the tool being designed does not just affect how the user carries out their work, it forms their perception of what the task is [32]. Finally, based on the importance of being able to communicate actions and decisions to multiple actors [36] and the need to evidence and comment on decision making for future learning [10], HMIs should include some capacity for annotation and onward dissemination of actions.  
To give the HMIs a specific focus, the application case for the pantograph RCM was the Tyne and Wear Metro. This light rail network covers 77.5 km (48.2 miles) and 60 stations, nine of which are underground. Rolling stock is powered by a 1.5-kV DC overhead line throughout. Metro cars are 40 metric tonnes in weight. Specifically, the application focussed  
Figure 3: High-level system view.  
on one of two lines (the 'Green' line) of the Metro, which connects Newcastle Airport with the city centre, and onwards to the adjoining urban centre of Sunderland.  
Following an iterative design process, designs were initially drawn by hand as low-fidelity prototypes. These were discussed between the authors, and further designs were implemented in Microsoft C# version 11. In a true user-centred design process it would be necessary to involve actual users as part of participatory design, but for this study the HMIs only needed to represent the functions between and within HMIs. These HMIs were further reviewed by two of the authors and assessed against usability heuristics [39] before a final set of designs were produced. These were interactive, in that it was possible to navigate between HMIs, and to access elements such as pop-outs and drop-down menus. The HMIs were not linked to a functioning RCM system.