Hi FloW, The reference resistor is key for having stable results. The initial accuracy can be calibrated, but the drift cannot. Usually higher precision resistor will have a better temperature coefficient. A 1% resistor will have 100-200ppm/deg C drift, whereas a 0.1% resistor will have 15 to 25ppm/deg C drift. Obviously the lower the drift number the better. When the SELFOCAL is issued, the contents of the OFC registers are updated to correct device offset. These register values are subtracted from each conversion result automatically. It is a good idea to set the PGA and data rate first before issuing the SELFOCAL so that the actual operating condition is used when calibrating the offset. When you connect multiple RTDs and measure them, you not only need to change the MUX0 register to the desired input channels, but also you need to make sure you are using the correct reference that corresponds to the RTD configured in the MUX1 register. Best regards, Bob B
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