>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 :-)
>
>--
>http://www.piclist.com hint: To leave the PICList
>.....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu
>
>
>
>
>
>
>

> -----Original Message-----
> From: pic microcontroller discussion list
> [PICLISTspam_OUTMITVMA.MIT.EDU]On Behalf Of Russell McMahon
> Sent: Monday, July 15, 2002 5:47 AM
> To: @spam@PICLISTKILLspamMITVMA.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 :-)
>
> --
> http://www.piclist.com hint: To leave the PICList
> KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu
>
>

> -> Russell McMahon wrote:
>
> >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

> >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 :-)
> >
> >--
> >http://www.piclist.com hint: To leave the PICList
> >TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu> > >
> >
> >
> >
> >
> >
> >
>
> --
> http://www.piclist.com hint: To leave the PICList
> RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu
>
>

>
>
> Yes.
>
>         RM
>
> --
> http://www.piclist.com hint: To leave the PICList
> KILLspampiclist-unsubscribe-requestspamBeGonemitvma.mit.edu
>
>

> to case was < 1200 VAC and > the normal mains voltage. The clearances are
> such i typical toasters (and, I' imagine, in this hypothetical one
   )
> that I suspect it may not arc during this test.
>
> I agree that total recall would be best.
>
>
>         Russell McMahon
>
> --
> http://www.piclist.com hint: To leave the PICList
> @spam@piclist-unsubscribe-request@spam@spam_OUTmitvma.mit.edu
>
>

>OK - here's "The Answer"
>As this is, of course, entirely hypothetical there is no one correct answer,
>but here's my take on it.
>
>I was highly impressed by all the suggestions. Tine domain reflectometry,
>resonance, even mechanical resonance, inductance, induced
>charge/fields/other. Many solutions may well have worked well. Some were
>indeed entirely non invasive.
>
>My own solution which works like a charm on the (entirely hypothetical)
>toasters is to use capacitance measurement (exactly as some suggested).
>
>Take a 3 pin mains socket with a short length (50 mm) of cord and two short
>wires A & B. . Connect Phase & Neutral to wire A and earth to wire B .
>Connect A & B to capacitance inputs on multimeter.
>
>For each toaster extract plug out of end of box and plug into cord end with
>prongs pressing through bag.. This slots the small plastic bag. It is most
>unlikely that customers will notice and less likely that they will care. If
>desired the bag could be removed for the test.
>
>A good toaster has a capacitance of about 180 pF (hyp-pF? :-) ) when the
>toast handle is up and around 300 pF when depressed. The up readings and the
>down readings are consistent within a few pF giving a very clear test.
>
>A bad toaster with one wire always connected to one of the two mains leads
>has a reading of about 300 pF with handle up and varies by about 2 or 3 pF
>with handle down.
>
>QED.
>
>Consistent results were obtained on a sample of about 30 good toasters and
>constant capacitance results on two sample faulty ones. A casual stroll
>through the toaster section of a local reseller toting a power socket
>equipped tester showed that the wide capacitance variation between up and
>down was present in all 15 or so models present. In all cases it was easy to
>predict whether the handle was up or down based on "up" capacitance alone -
>even without a "standardisation" pretest. This was true for models with from
>2 to 6 slice capability.
>
>As none were (apparently) faulty I could not establish how they would act in
>this mode but have no great reason to think that they would not exhibit very
>small capacitance change in that mode.
>
>Next challenge ? :-)
>
>
>         Russell McMahon
>
>Peter probably does not get a hypothetical fee as whistle blowers are
>usually not paid.
>
>--
>http://www.piclist.com hint: PICList Posts must start with ONE topic:
>[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> OK - here's "The Answer"
> As this is, of course, entirely hypothetical there is no one
> correct answer,
> but here's my take on it.
>
> I was highly impressed by all the suggestions. Tine domain
> reflectometry,
> resonance, even mechanical resonance, inductance, induced
> charge/fields/other. Many solutions may well have worked
> well. Some were
> indeed entirely non invasive.
>
> My own solution which works like a charm on the (entirely
> hypothetical)
> toasters is to use capacitance measurement (exactly as some
> suggested).
>
> Take a 3 pin mains socket with a short length (50 mm) of cord
> and two short
> wires A & B. . Connect Phase & Neutral to wire A and earth to wire B .
> Connect A & B to capacitance inputs on multimeter.
>
> For each toaster extract plug out of end of box and plug into
> cord end with
> prongs pressing through bag.. This slots the small plastic
> bag. It is most
> unlikely that customers will notice and less likely that they
> will care. If
> desired the bag could be removed for the test.
>
> A good toaster has a capacitance of about 180 pF (hyp-pF? :-)
> ) when the
> toast handle is up and around 300 pF when depressed. The up
> readings and the
> down readings are consistent within a few pF giving a very clear test.
>
> A bad toaster with one wire always connected to one of the
> two mains leads
> has a reading of about 300 pF with handle up and varies by
> about 2 or 3 pF
> with handle down.
>
> QED.
>
> Consistent results were obtained on a sample of about 30 good
> toasters and
> constant capacitance results on two sample faulty ones. A
> casual stroll
> through the toaster section of a local reseller toting a power socket
> equipped tester showed that the wide capacitance variation
> between up and
> down was present in all 15 or so models present. In all cases
> it was easy to
> predict whether the handle was up or down based on "up"
> capacitance alone -
> even without a "standardisation" pretest. This was true for
> models with from
> 2 to 6 slice capability.
>
> As none were (apparently) faulty I could not establish how
> they would act in
> this mode but have no great reason to think that they would
> not exhibit very
> small capacitance change in that mode.
>