> I would look at using a PRT stuck to the outside of the bowl, you could
even have a bunch of them around the outside

The bowl itself is double skinned and oil filled with heating elements at
the bottom. It does have a sensor and a PID temperature controller, and
maintains it's set temperature quite well. To test I painted a matt black
strip on the outside and checked with an IR sensor and FLIR - there is a
small temp profile across it's surface but it's quite good. But the
contents inside take time to heat and can be at very different temperatures
to the bowl itself/

For example, if I fill the bowl with 20l of water I need to set the bowl to
well over 130degC for the water to even boil within an hour even though the
bowl get' s there in 15 minutes. The time taken for heat exchange from the
bowl to the contents is significant and varies according to their mass,
volume (contact with the bowl?) and type, but since the contents are being
stirred they are quite uniform in temperature. Now if I want something to
be determined as "cooked" at 110degC there is no way (that I know of)
without actually measuring the actual contents.

Of course I could measure the temperature of the submerged inner surface of
the bowl which should be the same as the contents touching them, but that
is no easier than the contents themselves.
--=20
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