Delayed Feedback Makes for Difficult Troubleshooting

 

Looking at the first download of the washing machine usage data, I have found some problems: three of the five machines showed strange behavior: all hot or cold loads. That’s practically impossible and means something’s wrong.

Goddard Hall

5/11/2011 .. 5/17/2011

 

A

B

C

D

E

hot

0

17

23

0

85

cold

84

75

70

43

0

warm

0

15

10

0

0

Σ

84

107

103

43

85

 

There are several possibilities for things which would cause this kind of problem:

  1. Disconnected wire/broken wire or short
    This is easy to troubleshoot and fix. It is possible something came loose, and it would most handily explain the data error: if the hot wire
  2. Bad flowmeter
    without disconnecting the hose (hard to do), the flowmeter could either have an electrical fault or the meter wheel might not spin. Because I can’t easily run the machines, I can’t see what the problem is so easily. And this a difficult and/or expensive fix–I don’t have too many spares, the meters are $20 apiece, and the replacement requires some help from Hercules or the plumbing shop (due to liability issues).
  3. Hardware fault on the Arduino or Logshield
    I tested all of the Arduino+logshield dataloggers before deployment, and they passed testing for at least 24 hours of continuous use. It is possible that a fault developed, due to electrostatic discharge or other damage, but I think this is somewhat remote.
  4. Bad ground
    all of the flowmeters use a single ground plane—which would appear to work given that the problem is intermittent, but it could bear testing—some of the pins may have better connections than others. I’ll have to think about how to test this properly.
  5. Software fault
    The software should be good, considering the logging systems passed test. But I’ll rewrite the simulator to run through hot, warm, and cold loads to test the discriminator.

Lesson Learned

Building systems which don’t give real-time feedback are a problem (as one would expect) – getting all of the bugs out isn’t as easy as it should be, and this might be harder than it looks to perfect—which is the operative goal.

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