Interesting non-linear effects

[Karl W4KRL]

Bob,

Well, it is likely I read the meter wrong or wrote down the data wrong. It
is unlikely that the bulb has negative resistance. 

Karl W4KRL

-----Original Message-----
From: Bob Bruhns [mailto:bbruhns at erols.com] 
Sent: Saturday, November 10, 2012 11:41 AM
To: tacos at amrad.org
Subject: Re: Interesting non-linear effects

Looking at the chart in 'Light Bulbs.pdf', the Philips 100W 120V DuraMax
bulb seems to display a negative temperature coefficient of resistance
around 115V to 120V.  I didn't see this in the other bulbs that were listed.
The magnitude of the effect is relatively small, and it reminds me of
unexpected things that I see in many such seemingly simple measurements.

The dip at 120.8V is probably the result of a measurement recording or
transcribing error - if someone thought the notes said 0.89A when they
really said 0.84A, then the resistance calculation would have shown 144
instead of 136, and the graph would have been much more believable.  
(See attached spreadsheet.)  But maybe 0.89A was the correct reading, and
the dip at 120.8V was real.  I sometimes wonder how much information is
routinely ignored in day to day work.

    Bob, WA3WDR