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RTD and Thermocouple Remote Temperature Digitizer

Temperature Sensing Application Example

The LTC2449 is commonly used with thermocouples and RTDs as shown in this circuit. Thermocouple outputs produce very small changes (tens of microvolts per degree C) and the output will be negative if the thermocouple is colder than the “cold junction” connection from the thermocouple to the copper traces on the PCB. The RTD is measured by comparing the voltage across the RTD to the voltage across a reference resistor. This provides a very precise resistance comparison and it does not require a precise current source. Grounding the sensors as shown is a good fi rst line of defense for reducing noise pickup; however, the ADC must accommodate input signals that are very close to or slightly outside the supply rails. The LTC2449 handles these signals perfectly.