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Analog Angle

When Your Sensors Mislead You

Bill Schweber
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Michael Dunn
Michael Dunn
3/28/2013 2:36:09 PM
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Re: Bad sensors bite us all
More the latter. We had to ditch somewhere in Michigan, and I was stuck there all day. I seem to have blocked any other incidents from my memory.

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Brad Albing
Brad Albing
3/28/2013 2:35:17 PM
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Re: Bad sensors bite us all
Or perhaps just hot tea with lemon....

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Brad Albing
Brad Albing
3/28/2013 2:34:15 PM
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Re: Bad sensors bite us all
I had assumed it was bad karma. But could just be bad engineering.

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Brad Albing
Brad Albing
3/28/2013 2:33:04 PM
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Re: Sensors and fail safes
Crappy design on those smoke detectors. Where is Violet when you need her?

The Ultimate Question

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Brad Albing
Brad Albing
3/28/2013 2:30:16 PM
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Re: Bad sensors bite us all
What happened on the Airbus? Paying too much unwanted attention to the flight attendants? Or something of a more mechanical nature?

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Michael Dunn
Michael Dunn
2/12/2013 4:21:15 PM
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Re: Bad sensors bite us all
It's lateral thinking like that that got you to where you are today.

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Brad Albing
Brad Albing
2/12/2013 4:16:30 PM
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Re: Bad sensors bite us all
So, Boeing just needs to put their battery packs in the wings of the aircraft. There's an example of turning lemons into lemonade.

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WKetel
WKetel
2/7/2013 9:25:45 PM
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MIsleading data, or just plain wrong data
Sensors feeding digital logic systems have a number of different ways of providing wrong data. Sometimes the sensor is simply not able to function correctly in the actual environment, many times the power for the sensor is not just exactly as clean as the sensor requires for correct operation. On some occasions the wrong sensor is installed. And sometimes the parameter being measured is not the correct variable to be examined to gain the required information. That would llead to incorrect evaluation of wing icing, for sure.

In the case of the 787 batteries overheating, it is not clear as to if there was any sensor, and just where it was installed, if there was one, and what was done with the data it a proper sensor was correctly installed. The wrong processing algorithm almost always delivers a wrong answer, and that often leads to problems. This case does not seem to be an exception to that. So now the questions should be asked about what the process was for dealing with a hot battery. It seems that perhaps that is where the real failure will be found.

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Michael Dunn
Michael Dunn
2/1/2013 7:44:55 PM
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Re: Bad sensors bite us all
> Icing is good on cake, but bad on aircraft wings.

Wish I'd said that ;-)

Not exactly statistically significant, but the only bad airplane experiences I've had have been on Airbusses. Hmm... I guess Boeing Lithium Flambé would qualify as a bad experience too.

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eafpres1
eafpres1
1/30/2013 4:42:58 PM
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Sensors and fail safes
It would seem the ice sensors provide erroneous input, but it is the algorithm and resulting controls that cause the dive.  If you knew the sensor was giving wrong inputs, you could turn off the automatic control and at least avoid that problem.

Elsewhere I suggested in some systems that more mundane fail-safes be included instead of leaving everything up to software.  Even with good design and a lot of testing, software does unpredicatble things with unpredictable inputs.  Within the last 20 years, and possibly more recently than that, commercial pilots would come back and look out the windows at the wings.  Now they watch color displays.

I am bitten every few months by a sensor/alarm system that sees false positives and goes into alarm.  This usually happens in the middle of the night.  The system is the inerconnected smoke alarms in my house.  They are a bad design that is extremely sensitive to both the 9V battery condition and the line voltage.  At night the voltage seems to vary, and if the battery is even 6 months old they may go off.  I use a special Panasonic industrial battery to reduce the instance of false alarms.  But at least my house isn't going to fall from the sky.

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