Can we assume that the handles of the packed toasters
are all in the OFF position ?

Tal

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Russell McMahon
> Sent: Monday, July 15, 2002 5:47 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [EE]: Testing Challenge
>
>
> Here's a hypothetical (let's say) challenge.
> Consider it an example of a real world problem.
> Please ignore if of no interest.
>
> Problem: Propose a better test method.
>
> A manufacturer of domestic toasters finds that a large (many thousands)
> consignment of toasters has a fault.
> Many toasters are stored in a central depot but a significant
> number are now
> stored at several scattered locations a significant distance from the main
> storehouse. Skilled staff are probably not available at many locations.
> Conscientious and intelligent staff are deemed to be present at all
> locations (maybe a bad assumption :-) )..
>
> Each toaster has a double pole switch which disconnects the element from
> both leads of the mains cord when the toaster is plugged in and
> not in use.
> When the main "toasting handle" is depressed the two pole switch closes,
> passing mains power to each side of the element. (In all countries that I
> know of, all domestic toasters must have such a switch to meet regulatory
> safety requirements). In the faulty batch, in about 5% to 10% of the
> toasters, one or other pole of the two pole switch is
> mechanically jammed on
> due to a fault in the design and manufacturing process. The
> toasters that do
> not have this fault are entirely safe and meet all regulatory
> requirements.
> The toasters that do have this fault must be either repaired or scrapped.
> Each toaster is packed in a plastic bag and then in a cardboard
> carton. The
> bag is unsealed but to get access to the opening the toaster would have to
> be removed from the box. Removal and repacking takes time. The
> toaster has a
> non detachable cord which has a 3 pin plug (Phase, Neutral, Ground pins).
> The cord is packed at one end  of the box outside the plastic bag and the
> plug is pushed down with the cord. The plug can be pulled out a short
> distance to access its pins, if desired, without unpacking the whole cord.
> The plug is enclosed in a small plastic bag which is fastened at the cord
> end with a small rubber band.
>
> The test must reliably determine, at lowest cost in time and
> effort,  which
> toasters have one switch pole permanently closed so that one or
> other of the
> live leads is connected to the element.
>
> The brute force test solution is to unpack each toaster and test
> resistance
> from a point on the element to each of the two live mains pins.
>
> An alternative is to use sharp probes to poke small holes through the
> toasters' main plastic bags and plug bags to achieve the same test. This
> could be achieved without full unpacking at lower time cost but with
> slightly more skill in manipulating the conductivity tester. The
> acceptability small cosmetic damage to each bag by the test leads needs to
> be considered.
>
> SO
>
> YOU are asked for a better (faster, cheaper etc) way of doing this test.
> What do you propose?
>
>
>
>                 Russell McMahon.
>
> PS - I have absolutely no official or pecuniary involvement with domestic
> toasters :-)
>
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