This is the design for a thermometer. This circuit is work with based on LM392. The IC is used to provide gain and linearization for a platinum RTD in a single supply thermometer circuit which measures from 0 degrees C to 500 degrees C with g 1 degrees C accuracy. This is the figure of the circuit.
Q1 functions as a current source which is slaved to the LM103-3.9 reference. The constant current driven platinum sensor yields a voltage drop which is proportionate to temperature. A1 amplifies this signal and provides the circuit output. Normally the slight nonlinear response of the RTD would limit accuracy to about g3 degrees. C1 compensates for this error by generating a breakpoint change in A1's gain for sensor outputs above 250 degrees C. When the sensor's output indicates 250§C, C1's ``a'' input exceeds the potential at the ``b'' input and C1's output goes high. [Circuit’s source: National Semiconductor Notes].
Q1 functions as a current source which is slaved to the LM103-3.9 reference. The constant current driven platinum sensor yields a voltage drop which is proportionate to temperature. A1 amplifies this signal and provides the circuit output. Normally the slight nonlinear response of the RTD would limit accuracy to about g3 degrees. C1 compensates for this error by generating a breakpoint change in A1's gain for sensor outputs above 250 degrees C. When the sensor's output indicates 250§C, C1's ``a'' input exceeds the potential at the ``b'' input and C1's output goes high. [Circuit’s source: National Semiconductor Notes].
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