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Never trust a system that seems to be working

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Re: Never trust a system that seems to be working

#61

Post by hedora »

electroly wrote: post #43

This is why 4-20 mA is a common signaling standard in industrial automation. 4 mA means zero and 20 mA means one. 0 mA means broken transmitter !

It is also why white traffic lights no longer mean "go".

White means "the red glass lens in front of the incandescent bulb shattered again".

Related, from train signals:

> The invention of the track circuit in 1872 by William Robinson permitted automatic block signals. Most simply, a low voltage battery current runs up one rail and down the other. As long as current flows from the battery through one rail to the relay and back through the other rail, the relay remains energized and routes current from another battery to the green lamp of a clear signal. But when a train is present, the circuit is short circuited by the steel wheels and axles of the cars; a broken rail or an open switch will also break the circuit. As a result the relay is opened and the signal displays red. The system is arranged so the failure of any component results in a red indication or a dark signal (which must be interpreted as the most restrictive aspect that signal can display).

https://www.trains.com/trn/train-basics/abcs-of-railroading/...

Re: Never trust a system that seems to be working

#62

Post by shp0ngle »

teraflop wrote: post #56
shp0ngle wrote: post #26

Earlier quoted context omitted.

One dev said in one post that they like Uncle Bob. I think that’s it.

Well, that and a number of follow-up comments from the same developer, such as this one: https://www.reddit.com/r/factorio/comments/o2ly6f/friday_fac... A lot of people have (understandably) lost patience with the "just asking questions" style of rhetoric, and don't appreciate others making excuses for it.

No post body was provided.

Re: Never trust a system that seems to be working

#66

Post by yottabyte47 »

positr0n wrote: post #17

What drama with the Factorio devs is he talking about at the end (and namesearchers?.. I don't get Twitter sometimes) I've never heard anyone say anything about the Factorio devs except praise their productivity and professionalism.

foone's pronouns are they/them

Re: Never trust a system that seems to be working

#67

Post by peterleiser »

electroly wrote: post #43

This is why 4-20 mA is a common signaling standard in industrial automation. 4 mA means zero and 20 mA means one. 0 mA means broken transmitter !

Alarm systems use the "End of Line" resistor concept. The alarm triggers when a sensor is opened and current flow stops. Closed is ambiguous because it could mean power is flowing through all closed sensors OR there is a short (alarm panels handle shorts). A resistor allows the panel to consider 0 Ohms a short and some specific number of Ohms as closed and working. It apparently also provides a way to detect tampering of the wires.

https://www.alarmsystemstore.com/pages/all-about-resistors

Re: Never trust a system that seems to be working

#68

Post by mauvehaus »

janpot wrote: post #57
electroly wrote: post #43

This is why 4-20 mA is a common signaling standard in industrial automation. 4 mA means zero and 20 mA means one. 0 mA means broken transmitter !

or why we build a stop command with normal-closed contacts. a broken wire results in the same signal as a "stop" command.

If you're doing three-wire control [0], it also means you can add additional "stop" buttons by wiring them all into the circuit in series.

A nice-to-have addition to your table saw is a big red stop button you can reach with your foot so you don't have to take your hands off of your work pieces to shut the saw down if things have gotten more interesting than you expected them to. Three wire control makes this super easy to add (once you've found the big red mushroom-head n/c switch, of course).

[0] https://twcontrols.com/lessons/control-wiring-3-wire-control...

Re: Never trust a system that seems to be working

#69

Post by hardolaf »

elteto wrote: post #31

Wow, Factorio is approaching Full Time Job levels of detail and work required to keep everything running. Incredible game that I will never play, I feel I’m back at my job!

For most of these things, you just make a blueprint and stamp it down repeatedly.

Re: Never trust a system that seems to be working

#70

Post by kbenson »

pengstrom wrote: post #48
Karellen wrote: post #10

One reply tweet notes "a complex system always operates in a failure state", but to find more discussion on this point it's worth noting that this is a restatement of: > "The Fundamental Failure-Mode Theorem (F.F.T.): complex systems usually operate in a failure mode." -- John Gall, General Systemantics (aka Systemantics , aka The Systems Bible ), 1977 https://en.wikipedia.org/wiki/Systemantics > Searching for "funda…

The older I get and the more systems I encounter, the more I'm convinced everything is in a state of failing. The question is only how long before it becomes noticable.

Experienced sysadmins see the occasional chatter of problems in logs and emails as the pulse of the system, the EKG hooked up to the patient letting you know how things are going.

The right level of logging is usually enough to be annoying but not so annoying you need to reduce it. That means you're hopefully thorough enough in the logging that you're reporting what you care about and the things you see are the the things you can manually fix or ignore, and fit a frequency level you can live with.

Until the stuff you're managing becomes too large for that to make sense anymore, because that only scales so far (but surprisingly far for diligent admins). Then you need to move to something more complex, which is a big job and requires an entirely different way of reviewing (like Prometheus). You're probably better doing that from the beginning, but it's time and effort but everyone can take, or may not have existed at that time.

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