Circuit Project Electronic

In this circuit, the LT1025 cold-junction compensator provides the signal conditioning. The compensator’s voltage varies with the temperature of the reference junction in such a way that when summed with the thermocouple voltage, the combination behaves as if the reference junction were maintained at 0°C. (You should place the compensator as close as possible to [...]

Accuracy depends only on the tolerance of the nominal 10-to-1 R1/R2 ratio. Temperature-to-digital conversion involves a voltage-to-frequency-ratio scheme: Difference amplifier IC3 compares the square wave from Q1’s emitter to the signal developed across R3 by switches IC2A and IC2B, acting concurrently with R4, R5, and the 2.500V reference IC4 develops. IC3 amplifies the difference with [...]

The AD590 provides an output current proportional to absolute temperature (1 µA/K). In this application, the circuit offsets and scales the output to provide a full-scale range of 0 to 5V with a scale factor of 50 mV/°C over the chosen temperature range of 0°C—the freezing point of water—to 100°C, the boiling point of water. [...]