Blog Post
The Norman Distributed Control System

The Norman Distributed Control System

Stephen Reilly, ProSys

I recently came across a video about the frustrating design of Norman Doors in various buildings that made me wonder if I have encountered Norman-like design in the distributed control systems (DCS) I have worked with. For those unfamiliar with the term, it’s named after Don Norman, author of The Design of Everyday Things, and a “so-called ‘Norman Door’ has design elements that “give you the wrong usability signals to the point that special signage is needed to clarify how they work.”1   For example, the “push” or “pull” sign is needed.

In order to compare this to a DCS, we first need to address what Norman expounded in his book. In it, he introduced the term of affordance, originally conceived by American psychologist James J. Gibson, as it applied to design, elaborating particularly upon the perceptual dimension to the concept. As an example, he explains that it is “dependent not only on the physical capabilities of an actor, but also the actor’s goals, plans, values, beliefs, and past experiences. If an actor steps into a room with an armchair and a softball, [the] original definition of affordances allows that the actor may throw the chair and sit on the ball because this is objectively possible. Norman’s definition of (perceived) affordances captures the likelihood that the actor will sit on the armchair and throw the softball.”2 Norman also emphasizes the importance of user-centered design, which “involves simplifying the structure of tasks, making things visible, getting the mapping right, exploiting the powers of constraint, designing for error, [and] explaining affordances”.3

So what would you perceive a distributed control system’s affordances to be? Well, to me, some that especially stand out are:

  • To record and display process measurements obtained throughout the facility
  • To apply control changes that impact the process when desired by the user
  • To alarm off-target process conditions that put the company and/or its employees at risk

While I am thankful to say that all of the DCSs I have worked with promote these affordances, there is plenty to be desired regarding their user-centered design for their human-machine interfaces (HMI), a.k.a. their operator displays. At ProSys, my coworkers and I often use Interface Dynamics version 3.0 (IDv3) on the HMIs we create, remaining conscientious of such user-centered design elements4 such as:

  • Visibility – To provide accurate models of what is sequentially happening in a client’s facility
  • Accessibility – To find information quickly and easily throughout the displays in a meaningful and consistent navigational hierarchy
  • Legibility – To clearly and concisely present operational data in a readable format that doesn’t clutter the client’s view of their process

Thus, if your HMI could use some improvements to prevent your system from becoming a Norman DCS, consider reaching out to us.

References

  1. ISBN 0-465-06710-7
  2. https://en.wikipedia.org/wiki/Affordance
  3. https://en.wikipedia.org/wiki/The_Design_of_Everyday_Things
  4. https://en.wikipedia.org/wiki/User-centered_design
  5. Image: http://www.slideshare.net/jonfroehlich/moving-beyond-line-graphs