Downtime reduction

We have in the past moved towards more sensors for easier troubleshooting. For machines operating in a "difficult" environment, we found we got more defects/errors and they were harder to track down. Quite the contrary of what we were aiming for. At some point, most of the errors you get are sensor defects (either the sensor itself or the cabling). Since then we have backed off, limiting sensors to what is critical for the process at hand. For our customers, most of the time less sensors is a more reliable machine. This depends very much on the environment and the process though.

You see a similar thing with cars in the last one or two decades. Cars with lots of electronic monitoring tend to have more defects. In the electronics, "ghost" warning signals while there is actually no defect. Some (mind you, not all) "cheap" lines or brands have proven to be significantly more reliable than upmarket models stuffed with electronics. If it is not in there, then it cannot break.

I agree with you that there is a point in not having more sensors than needed however cars is a very bad analogy because compared to industrial machinery a car is a pretty crappy piece of machinery and very cheap too.

The industries I worked in where failures matter are all running 24/7/365. Every valve, every pneumatic cylinder, every circuit breaker, every VFD, basically everything has some kind of sensor on it so there is some kind of way to detect an error. Sometimes there is a sensor problem but the most common reason for that is actually mechanical (mounting) or purely using the wrong sensor for what you are trying to detect. The cost of putting a sensor somewhere is much higher than the cost of the sensor itself so they always use high quality stuff, no no-name china stuff.

BTW, just recently I was looking at the maintenance history of a machine that has been running round the clock for about 15 years, that's roughly 130 thousand hours of operation. In those years about 5-6 sensors (it has photoelectric, inductive, laser, ultrasonic, magnetoresistive sensors and pulse encoders) had been replaced. I estimate it has a total of around 100 sensors of this kind. Then there are about 100 input signals from circuit breakers, isolator switches, VFDs, contactors etc. I think the failure rate is very acceptable.
 
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Bahaha, I love it.
"We keep blowing fuses when equipment fails, let's get rid of the fuses."
"I keep cracking my helmet when i fall off my bike, I'll get rid of my helmet."
"I keep having broken Kevlar vests.."
"The climbing ropes are only rated for one fall of 5m or more.."
"The brakes on my car keep wearing out..."

I had a similar conversation with my wife one night after she cracked the screen on her phone. "Why didn't you have the protective case on it?" "It kept breaking so i took it off." o_Oo_Oo_Oo_O
 
Sometimes all the diagnostic tools and alarms in the world can't help some operators.

The last line I did has an HMI troubleshooting page, it blatantly says in flashing letters...."Main motor disconnect is off" also states "Line is not ready to run" and pressing the start button in this state generates an alarm that states... "Main disconnect must be turned on before starting" and still, the operator doesn't know why he cant run the line. When I come and turn on the disconnect on then start the machine, he looks dumbfounded. When I look at the alarm history screen, I see that he acknowledged the alarm 12 times and re-tried to start the machine just as many before calling me.
How can it be any more obvious???? I'm thinking about alarm driven shock collars but my safety manager says no.. Hmmm.
 
Pete, I think as with so many things in life and more specifically in our work: it depends. Perhaps the car analogy wasn't exactly the right choice but let me put some things in perspective. Our machines go all over the world, often somewhat remote locations with no qualified maintenance staff nor parts supply. If we are lucky, there is one guy with a bit of good sense and a few technically enlightened brain cells in the skull. Other than that the circumstances are rough and so are the people that work there. We cannot fly out to every little defect. Even though industry quality sensors are indeed robust beyond doubt, you wouldn't believe what some of our installations look like after one year of negle.... eehm proper good use. In some of these places anything on it that can break, will break. So these days we limit sensors to the minimum that is required for proper and safe use. If the client wants more and is prepared to pay for it, usually means they have some staff that understand the reason for those sensors and take good care of them. In those case, we are happy to add more and monitor them in the software. Among our clients they are a minority though.
 

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