2 Operating Information
30 U2000 Series Operating and Service Guide
Internal and External Zeroing
Zeroing a power sensor is performed in order to reduce zero measurement
offset and noise impact to improve the accuracy of RF power
measurement. The U2000 Series USB power sensors have two types of
zeroing; internal zeroing and external zeroing.
Internal zeroing is a new type of zeroing process whereby RF/Microwave
power can be left connected to the sensor while it is being zeroed. High
isolation switches are opened in the sensor to isolate the diode sensor
from the electronic circuitry. With the available processing power from the
embedded DSP in the sensor, the internal zeroing algorithm is applied to
the internal zeroing data. Hence, internal zeroing provides the convenience
of performing a zero with the RF/microwave signal present. This feature
makes internal zeroing more convenient, but one may only use internal
zeroing if zero set (internal) is within the user's application requirements.
External zeroing process is a two- step process. The RF/Microwave signal
to be measured must be removed from the sensor and then the sensor can
be zeroed. Do not apply any RF/microwave signals to the RF input port
during external zeroing process. Any RF/microwave signals pick- up by the
diode sensor during external zeroing will be considered as part of the
noise. External zeroing generally has better zero set performance. The
internal or external zeroing selection should be made based on the
measurement needs.
Users can choose to use either internal zeroing or external zeroing. The
sensor is defaulted with internal zero every time it is powered up.
Figure 2- 4 shows the illustration on how to set the external zeroing if the
N1918A Power Panel tool is used.
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