Hi Russell,

I am really curious to know what motivated this challenge? I had thought
that it was similar to some problem you are actually facing. Did you
actually make the measurements you mention in this email?

Sean

At 09:47 PM 7/16/2002 +1200, you wrote:
>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.
>
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