If the internal temperature sensor is used for cold junction compensation, MAX31856 will assume that the device temperature and cold junction temperature are the same. When the connection is made in the manner suggested in the question, the cold junction temperature and the temperature sensed using the internal temperature sensor will be different, leading to an error in temperature measurement. For this scenario, it is suggested to disable the internal cold-junction sensor and use an external temperature sensor at the actual cold junction instead. Then, write the temperature reading of this sensor into the cold junction temperature register regularly.
