The Condition Monitoring and Diagnostics Coma

It’s one of those geeky subconscious thoughts that you have while you are doing something else. Distracted, you don’t even realise your mind has wondered into the subject until the thought resurfaces later and you track it back to what fired it in the first place. The philosophy of machine maintenance.

During a conversation my eye is drawn to the worn truck tire behind the guy I’m talking with. The conversation continues while I’m looking at the construction of the cross matting visible where patches of rubber are missing, thinking about how many plies the tire has, how much rubber is left before the steel inserts pop through, and if the rolling surface will puncture before the cracked sidewall splits over a pothole. It’s a 13 tonne Indian truck which means it’s probably loaded with about 40 tonnes. My guess is the side wall will go first. In fact my guess is that the side wall should have gone a long time ago.

When I was starting my brief career as a manufacturing engineer, Planned Maintenance (also known as Preventative Maintenance or PM) was the newest thinking from Japan. By having a schedule for maintaining your machinery you could pre-empt breakdowns and reduce the lost running time, increasing the Mean Time Between Failure (MTBF) of your line. I was never that convinced that applying PM to every machine was for the best. It meant stopping the lines to fix things that weren’t necessarily broken, and with some machines they’d spend more time stopped for maintenance than they ever would have for unexpected breakdowns.

The secret was to have a good PM schedule, that understood the design of the machinery and the lifespan of the components, but even then, the rated lifespan and load tolerances of components are always underestimated with safety factors so PM schedules are inevitably an overcautious approach. Nonetheless from a commercial point of view having a line stop when you are expecting it costs a lot less than having a line stop when you aren’t, so PM makes good businesses sense.

And then Condition Monitoring and Diagnostics was born. CMD involves having sensors on machinery that give you an indication they are about to fail. For instance you might have a vibration sensor on a bearing that detects the increase in vibration which indicates it’s worn and about to fail. Marry that with a neural logic controller that learns how to predict failure rates based on the severity of the vibration and you have a system that can dynamically extend the schedule for maintenance shutdowns if the machine is running fine.

The dashboard indicators on cars that tell you when to service the vehicle work on similar principles, but they are mainly dictated by time elapsed and miles covered, unless something starts to go badly wrong in the meantime.

I don’t have a PM schedule for the bus other than regular servicing, oil and water checks, and I certainly don’t have a CMD controller in my 1989 truck. So my approach is similar to the Indian truck drivers that listen out for problems and carry enough tools to fix whatever situation might arise. I’ve seen drivers rebuilding engine blocks by the side of the road. I couldn’t do anything that extreme, but I don’t quite have the drive-it-to-destruction attitude that the truck tires here suggest, so hopefully I won’t need to.

Effectively I am the CMD neural logic controller. My ears and arse are the sensors that listen out for new noises and vibration, my right foot detects changes in performance and my hands feel for alterations in the handling. Any new behaviour is worrying, but unlike a well designed CMD system I’m not necessarily able to immediately identify what’s causing the symptom. In Turkey I first noticed a squeak from the alternator bearing. I wanted to change it there and then, but the mechanic I showed it to said it would last for 5000km. That was 8000km ago and it’s not getting any worse. That’s my neural feedback loop, learning how the extremity of the symptom relates to the remaining lifespan.

My journey isn’t paced against a tight schedule. I don’t have to be somewhere at a given time, so I can afford to have unexpected breakdowns which delay me. In fact as long as they don’t happen too regularly I love them when they do happen as it flings me into a new adventure with new people. Heidegger, a German philosopher said our minds function in an auto-pilot sub-consciousness most of the time until things don’t work as we expect and then we have to snap out of our slumber and actually think. Opening your front door is an automatic action that doesn’t require thought, but imagine the key won’t turn. You have to mentally change your plan, from entering your house, to figuring out how you are going to open the door. He called that moment “breakdown”.

Mechanical breakdowns cause me to snap out of my slumber and look again at where I am and what my plan is. I think Heidegger said that these moments of breakdown are the only times when we are really alive. If he didn’t say it, then I do. CMD, and the other engineered solutions that keep things running to the expected standards, and without surprise interruptions, also keep us in a relaxed mental state where we don’t have to think. Kind of like a coma. Maybe knowing you are only one pot hole away from a deadly 40tonne blowout conversely keeps you alive.