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  • MCP6V01 Auto-Zeroed Thermocouple

  • Created: May 01, 2017

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Auto-zeroed amplifiers are composite amplifiers that use digital circuitry to dynamically correct for analog offset errors. The ultimate advantage of this type of amplifiers is its extremely low offset voltage. This reference design uses MCP6V0 operational amplifiers, which has input offset voltage correction for very low offset and offset drift. This op amp operates with a single supply voltage as low as 1.8V, while drawing 300 µA/amplifier (typical) of quiescent current.

This reference design demonstrates how to use a difference amplifier system to measure electromotive force (EMF) voltage at the cold junction of thermocouple in order to accurately measure temperature at the hot junction. This can be done by using the MCP6V01 auto-zeroed op amp because of its ultra low offset Voltage (VOS) and high common mode rejection ratio (CMRR). Ambient temperature is measured using the MCP9800 temperature sensor that is located as close as possible to the connector on the PCB. This measurement is used by the PIC18F2550 to perform cold junction compensation for the thermocouple measurement. The RC low-pass filter that is implemented in this circuit can remove the high frequency noise and interference from the signal path prior to the analog-to-digital (A/D) conversion. The PIC18F2550 microcontroller communicates with the MCP9800 device and completes the analog-to-digital conversion. The VREF of the 10-Bit ADC is 4.1V provided by MCP1541 Voltage Reference. The measured data will be transferred to the PC using the USB interface.

Auto-zeroed amplifiers are used in systems with an expected design life of greater than 10 years and in signal chains that use high closed-loop gains (>100) with low-frequency (<100 Hz), low-amplitude level signals. Examples can be found in precision weigh scales, medical instrumentation, precision metrology equipment, and infrared-, bridge-, an thermopile sensor interfaces.