At 03:24 PM 2/17/2000 , Davidson wrote:
>what is a thermistor??
>Bill

It's a special resistor made of a material that exhibits an unusually large
resistance change with temperature, usually less resistance with higher
temperature (which is backwards of most materials).  This slope direction
is called "negative temperature coefficient."  The device may be the size
of a pinhead or much larger, and often is embedded in a case like the
Vanagon Temp I and Temp II and gauge senders are.

Among other uses, it's one of the two common methods of measuring
temperature electrically -- the other way uses a thermocouple, which is in
essence a pair of dissimilar wires joined at the ends.  They generate a
(tiny) voltage which is proportional to the temp. difference btw the hot
ends and the cold ends.  The thermistor method is generally cheaper and
less accurate, and requires external power (easily available in a
vehicle).  Also  a thermocouple will probably withstand temps that would
destroy a thermistor.

Incidentally if you look at the resistance vs temp charts in Bentley,
you'll see that Temp I and Temp II have the identical characteristics,
though their external appearance is different.  Very likely the actual
thermistor is identical in both.

david
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"