Why is sensor with internal calibration capability not measuring 0dBm after performing zero & calibration process?

Power sensors with internal calibration capability( eg. N192XA, U848x, U2020XA, U2040XA) use its built in reference when performing a zero and calibration. This feature eliminates multiple connections with an external calibration source, with the benefits of reduced measurement uncertainty, reduced connection wear and tear and faster test time. Sensor accuracy is adjusted based on its characterized data stored inside sensor EEPROM instead of power meter’s 50MHz reference. This will potentially result in a reading which is not measuring 0dBm and less comparable to those achievable by sensors with external calibration capability since the measurement is dependent on both the characterized data of the sensor itself as well as the accuracy of the power meter’s 50MHz reference. User to refer to the expanded uncertainty computed with measurement uncertainty calculator of those models for its acceptance criteria.

Power sensors with external calibration capability( eg. 848X, E930X, E441X, U848X) use the power meter’s 50MHz reference when performing a zero and calibration. Sensor accuracy is adjusted based on power meter’s 50MHz reference. This will result in a perfect 0dBm reading by offsetting the error from 0dBm during calibration.

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