Re: [SystemSafety] power plant user interfaces

From: Matthew Squair < >
Date: Mon, 20 Jul 2015 08:38:36 +1000

A good example of metaphor is 'Object Oriented Design' in software, of course there's no such thing as a software 'object' but it it is a very powerful programming metaphor.

Matthew Squair

MIEAust, CPEng
Mob: +61 488770655
Email; Mattsquair_at_xxxxxx

On 20 Jul 2015, at 8:22 am, Steve Tockey <Steve.Tockey_at_xxxxxx

Seems you and I have different definitions of "metaphor". Again, "metaphor" means using something people are already familiar with to help them understand something they aren't familiar with. The network switch to railroad switching yard was my earlier example. Metaphor always involves "the A that you don't know is like the B you do know". IMHO, the helmsman's trick would qualify as a "heuristic", not a metaphor. The spreaders aren't "like" west, it's just a convenient way to help solve a problem (which is what a heuristic does).

 One of my hobbies is home brewing beer. The temperature of the water when it's mixed with the malted barley is fairly critical, 175F to 180F. When water is being heated to boiling, the surface gets as smooth as glass when it's in that range. That's how people made beer before thermometers were invented: heat the mash water to the smooth-as-glass point and then add the malted barley. "Smooth as glass" is a metaphor for understanding the appearance of the water, however it's use in brewing is as a heuristic because it indicates when to mix in the grains.Said another way, "(Heuristic: add the malted barley to the mash water when the surface of that water is (metaphor: as smooth as glass))"

 On your negative example, my understanding is that design criteria for private planes (and, thus, ultralights?) is that they have positive stability. Just let go of the controls and the airplane is designed to return to straight-and-level. Of course this doesn't help if there's something to run into, but it does solve the loss of orientation problem. Just trust physics to point you back at level and hope to run out of cloud before you run out of airspace (better yet, stay the h--- away from clouds unless you're instrument rated and in an IFR equipped plane).


  From: Les Chambers <les_at_xxxxxx Date: Thursday, July 16, 2015 5:59 PM
To: Steve Tockey <Steve.Tockey_at_xxxxxx Cc: Matthew Squair <mattsquair_at_xxxxxx systemsafety_at_xxxxxx systemsafety_at_xxxxxx Subject: Re: [SystemSafety] power plant user interfaces

  Thanks for this Steve
An excellent set of pointers to good HMI design.  I hold to my initial proposition though. That the metaphor is at the root of all HMI design. It is not something off to one side. All your points are either an attribute of a good metaphor or an analysis process that yields a good one.
The metaphor is at the nexus of human cognition and the real world. It's quality is the core objective in HMI design. Case study:
1. The negative example: most ultra lite aircraft are not fitted with instruments. Any UL pilot will tell you that if you fly into cloud you have around 90 seconds to live.
2. The positive example: All helmsmen will tell you that the most potent metaphor for due west in the northern hemisphere is the position of the constellation of Orion relative to the mast in the hours before dawn. Put the three stars of Orion's belt underneath the spreaders and you are dead on course 270. It's primal, even beautiful, and real time, unlike the compass or digital readouts which have a lag.

 When we find the good metaphor we've invested substantial intellectual effort in discovering the truth. And the truth is what an operator needs, especially in emergency situations when there is no time to think.


Les Chambers
Chambers & Associates Pty Ltd
0412 648992

On 17/07/2015, at 5:43 AM, Steve Tockey <Steve.Tockey_at_xxxxxx

Yes, I'm here. Just too buried in travel and client work to spend the time responding to this one…

 "So my point is: the key to a good HMI is excellent metaphor design. The FAA standard lists all the HMI Lego blocks in stupefying detail but there is no guidance on how to assemble them into a compelling metaphor. Where is the standard for that?"

 I'll agree that excellent metaphor is A key, but it's not THE key. Other things are entirely relevant. Here's a good quote to start things off:

 “The most powerful interaction design tool used by the authors is simple on the surface: a precise descriptive model of the user, what he wishes to accomplish, and why.”
—Alan Cooper & Robert Reimann (From *About face 2.0: the essentials of interaction design*. New York: Wiley, 2003. ISBN 0764526413)

 I'm a huge fan of doing "Task Analysis". Task analysis examines both the work to be done and the work environment to better understand the context of the system and its requirements—particularly user interface requirements. There's a description of Task Analysis in section 7.6 of "Human Factors Methods for Design: Making Systems Human-Centered" by Christopher P. Nemeth.

 In addition, here are eight useful principles from Ben Schniederman:

 Strive for consistency
Enable frequent users to use shortcuts
Offer informative feedback
Design dialogs (read: interactions) to yield closure  Offer error prevention and simple error handling Permit easy reversal of actions
Support internal locus of control
Reduce short-term memory load

 Here are the first 10 of 30 principles from Paul Heckel (*The elements of friendly software design: the new edition*. San Francisco, CA: SYBEX, 1991. ISBN 0895887681):  Know your subject
Know your audience
Maintain the user’s interest
Communicate visually
Leverage the user’s knowledge
Speak the user’s language
Use metaphors
Focus the user’s attention
Anticipate user’s perceptual problems
Communicate only if you can

 So my point is that while a good metaphor is very important, there's a lot of other stuff that's also very important. Starting with a good task analysis, and using the kinds of design principles here (and from Norman's Design of Everyday Things), one can then assemble the Lego Blocks in the FAA standard to build an effective interface. Well, or at least have a better chance of not doing something stupid…


  From: <systemsafety-bounces_at_xxxxxx Les Chambers <les_at_xxxxxx
Date: Tuesday, July 14, 2015 6:12 PM
To: 'Matthew Squair' <mattsquair_at_xxxxxx Cc: "systemsafety_at_xxxxxx systemsafety_at_xxxxxx Subject: Re: [SystemSafety] power plant user interfaces


Just so. I'm in furious agreement.

Not long ago I spent 40 hours on the helm of a yacht crossing the Atlantic. The yacht had no autopilot. It occurred to me one night, "My God, I am become an automaton", which led me to the following thought process that may shed light on the fundamental quality factors in HMI design.

Picture life as a control system. Your job is to ride herd on some equipment against the constraints that the humans have given you. All you can see are a few measured variables. It's like looking at life through a straw. All you can do is pull some levers that the humans have given you. If the behavioural model of the equipment under your control matches well enough with real life, the script the humans gave you (read control algorithm) has a chance of working. There are a few things in your favour. You are attentive 24/7, you never fall asleep. You can also respond to disturbances in milliseconds. You're capable of processing large amounts of data and taking many control actions almost in parallel. That is of course if your model is a good reflection of real life. The model can be as complex as you like, just as long as you can run it in real time.

Your other job is to pass on a simplified picture of what's going on to the humans. And you do this through a user interface. The humans are stupid and slow, prone to sleepiness with an unhealthy penchant for sex, drugs and rock 'n' roll. They're also carrying a lot of distracting baggage: mortgages, family dramas, gambling habits. They don't have your eye for detail and may panic and run when things go pear shaped. So if you can possibly help it, don't bother them with drama unless it is absolutely necessary. Even if you are not feeling well, heal yourself and tell the maintenance guys later. They tend to be the more rational of humans.

But take pity on the operators because they are looking at life through a straw also, the one you gave them in the HMI. So what you give them had better be rich in simple metaphor, explaining a lot with a little. A Metaphor is no good if you've got to explain it to someone. They need to glance at it and say, "Oh yeah, I got it, life's like that." This is why drag and drop has been so successful. This is why the concepts of "reactor step", and "sequence control unit" were so successful in chemical reactor operations. They were a simplification of the concepts of state and state engine, Mealy models, Moore models Harel state charts and the like. It was all the operators needed to know through their narrow straw, the one we gave them in the HMI.

So my point is: the key to a good HMI is excellent metaphor design. The FAA standard lists all the HMI Lego blocks in stupefying detail but there is no guidance on how to assemble them into a compelling metaphor. Where is the standard for that?

Steve. Hallo. Are you there?


*From:* Matthew Squair [mailto:mattsquair_at_xxxxxx *Sent:* Tuesday, July 14, 2015 9:52 PM
*To:* Les Chambers
*Cc:* Gergely Buday; Gareth Lock;

*Subject:* Re: [SystemSafety] power plant user interfaces

Actually a HMI is a little more than 'just a window'. I think you're looking in the wrong direction.

Complex HMI actively mediate the interaction between the system under control and the operator. The more complex that mediation, the more the operator must herself maintain a model of the interface not just the system under control.

So you have to not just make the system under control understandable to the operator, so that they can do their job, but also do the same for the interface. That requires a very good practical understanding as to how people think, perceive etc, etc, a bit more than the 'ilities', some call it cognitive engineering.

Matthew Squair

MIEAust, CPEng

Mob: +61 488770655

Email; Mattsquair_at_xxxxxx


On 14 Jul 2015, at 8:55 am, Les Chambers <les_at_xxxxxx

 Can we get back to first principles here. A human machine interface (HMI) is just a window into a process that allows human beings to observe what's going on, understand what's going on and manipulate what's going on (when human intervention is required) such that the target system succeeds in its mission (in our case, without killing anyone).

A 'good' HMI therefore supports: observe-ability, understand-ability and control-ability
If you like the devil is in the 'ilitys'

After 10 years working with chemical processing reactors of all levels of complexity, sizes, shapes and chemical processing technologies, followed by a further few years working in wide area control systems in the rail industry, interspersed with a year working on development standards for computers in the shutdown loop of nuclear reactors I have concluded the following:

A groovy HMI (with all the right contrast ratios and menu hierarchies) is useless if you don't have the instrumentation to observe what's going on in the process. Case study: QF32 would not have had an engine explosion if Rolls-Royce did a mass balance around the lubricating oil flow in their jet engines. A mass balance would have revealed an oil leak that ultimately caused the explosion and the near death-experience of 300 odd people. Further, these days, just the presence of sensors is not enough. You need the computing power to calculate secondary variables such as mass balance and rates of change. It can get even more complicated in chemical processing when the output of chemical analysis equipment requires significant processing to come up with numbers that mean something to human beings. Some of these numbers need to be calculated at high rates depending on the time constants of the target process. A simple example: in a latex reactor control system I once worked on the most important number in the plant was the rate of change of reactor temperature. It was a lead indicator of trouble, maybe 6 to 8 hours in the future. My point is that the HMI could display this number in the most primitive and clunky way and it would still be a potent tool in man machine interface. The fact that it existed was most important, not the way it was displayed.

In response to those who might say, "Aw shucks these systems are highly complex these days and operators can easily get confused. Gees look at what happened at Chernobyl and Three Mile Island. " ... I say, "squeeze out the tears you sorry bugger."
Professional control systems engineers have known for years that highly complex systems can be simplified using the right metaphors in design. Cooperating state engines is one good example that is pretty well universally applied. ... Although some industries do go through dark ages where this is forgotten. For example in one project I actually had to fight to universally apply this model across a smoke extraction system. In the end I won by pulling rank and (metaphorically) executing anyone who disagreed with me.
My point is that at the root ball of understand-ability is the ability to understanding system state. And you cannot achieve this without a well thought out design using a state model.
Returning to the latex reactor, in common with every other chemical processing plant I ever worked on, apart from some critical raw or calculated process variables, the next most important set of numbers was the state of each unit operation in the process (we called it the step number – a concept easily understood by anybody). If the controls for these unit operations were implemented with state engines this became a simple matter. Some operations (the ones that were potentially explosive) were more critical than others. So you could walk into a control room look at a couple of numbers and very quickly get the complete picture of where the plant was up to, or if it was, in fact, in a dangerous state. It was observe-ability heaven!
Once again, the display of these numbers could be as clunky as you like the fact that they existed was the important thing. And they would not have existed without a design totally focused on understand-ability through human friendly metaphors.

Once again a groovy HMI is useless unless you have the final control elements to actually control the process. In chemical processing this took a massive leap of faith as large sums of money had to be spent on installing elements such as control valves that could be manipulated by a computer. It got so expensive that 30 percent of plant capital went into instrumentation and final control equipments. Just the act of running a pipe down off a pipe rack and installing a control valve with all its associated block and bleed equipment could cost upwards of 20,000 dollars (in the 1970s).
Another thing I noticed about controllability is that the less control you give to a human being the better of you are. I experienced some plants that could not be manually controlled by human beings. One tubular reactor a colleague worked on could only be controlled by a computer algorithm. If the algorithm or the field equipment looked like it was failing they would shut the plant down.
Here's the interesting thing: once you're committed to proper instrumentation and final control elements, computers, and state engine models you tend to take it all the way and make automation total. Google and friends have reached this conclusion with the automobile. The less our hands touch the steering wheel the better off we all will be. (I invoke a previous post, the aphorism from Apocalypse Now: never get out of the boat, absolutely god damn right, unless you're prepared to take it all the way. No matter what happens.)
One downside of total control is that operators need to understand what is going on in the rare situations where they need to intervene. I am told that the most common explicative in an aircraft cockpit is, "What the f... is it doing now?" Once again this is where good metaphors in design play a critical role.

A note on engineers not understanding user needs. In my experience this was solved by chemical plant engineers actually writing the control software after appropriate training in control theory and the target computer control systems. Plant engineers were then responsible for maintaining their own software. Unfortunately this is impractical in other domains such as aviation. I will say one thing though, understanding fundamentals of any process, chemical or nuclear, is one thing but knowing how to control it safely is another. In operating any process you need to look at it from the point of view of set points, measured variables, lead and lag indicators, time constants, dead time, gains and rates of change. I found this perspective missing in a lot of plant engineers, that is before they were properly trained in control theory. Some of them seemed helpless to solve their process problems purely because they were looking at the issue through the eyes of a control Systems engineer. Indeed Chernobyl was a result of some punter not understanding that running those reactors at low power created an unstable system which got out of control and ran away when they attempted to control it manually (just like the tubular reactor I mentioned above).
There is also a dilemma here which I experienced many years ago when it fell to me to train operators in technologies and ways of operating that they could not possibly visualise with their current experience. Henry Ford framed it well (with a metaphor of course): "If I asked them what they wanted they'd tell me, 'faster horses'." There is an element of this in many new things we design these days. For example Steve jobs never had focus groups. Page, Brin and Musk at some point in their careers were all viewed as crazy (Musk once asked his latest biographer, "Am I crazy" as if he was unsure himself).

I had a quick flip through the FAA Human Factors Design Guide. All good stuff but I noted that none of the above issues were addressed. It's like I was reading the syntax manual with the bit on semantics missing. Was all that stuff in another chapter? Tell me it was mate or are we entering another dark age.


-----Original Message-----
From: systemsafety-bounces_at_xxxxxx mailto:systemsafety-bounces_at_xxxxxx <systemsafety-bounces_at_xxxxxx Buday
Sent: Tuesday, July 14, 2015 5:44 AM
To: Gareth Lock
Cc: systemsafety_at_xxxxxx Subject: Re: [SystemSafety] power plant user interfaces

On 13 July 2015 at 21:27, Gareth Lock <gareth_at_xxxxxx

 The answer is yes, but one of the problems is that engineers are not normally users, so they have a different perspective on what short-cuts or ‘misuse’ might happen. This means that the end user needs to be engaged in the design process too but from my perspective, they aren’t normally that bothered because they can’t see or touch it. In addition, we sometimes get into the ‘but why would anyone do it that way, I designed it this way!’ discussion!

I do not want to hijack the seriousness of the conversation but that reminded me of this:

The System Safety Mailing List

The System Safety Mailing List
systemsafety_at_xxxxxx Received on Mon Jul 20 2015 - 00:38:49 CEST

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