The circuit of the Celsius thermometer
in the diagram is based
on the well-known Type LM334
from National Semiconductor.
This IC is a sensor that provides
a current which is directly proportional
to the temperature in
kelvin (K). Unfortunately, this is
a quantity that is not suitable for
use in most practical applications.
In the circuit, therefore,
the sensor is set to 1 µA K–1
with P1 and the offset of 273 K
removed with P2. This renders
the output voltage of the sensor
directly proportional to the temperature
in degrees Celsius (° C)
and this makes the circuit suitable
for a great many applications
(since 1K=1° C).
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