"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message
news
RST Engineering (jw) wrote:
Is it purely a function of the size of the metal piece, or is the type
of
metal part of the equation?

The other thing I don't understand is that if I do a good job of
insulating the metal piece from ambient how it won't eventually come to
the same temperature as the head.


If you mount the sensor in a bar that is picking up heat at one end, and
losing heat at the other - you sensor will read somewhere between the two
temperatures. But, if you don't know a lot about the heat transfer rates
at
each end, you will not know how the temperature your sensor sees is
related
to the temperature you want to measure.

Think of a series voltage divider with two known resistors in the middle
and
an unknown resistor attached to each end. What does the votage measured at
the junction between the two known resistors tell you about the source
voltage?

how about two temp sensors at measured intervals along the insulated bar,
then assuming the temperature gradient is constant along the bar, you can
work out the temp at the cylinder head.

Colin =^.^=