user manual

46 Chapter 3
Test Set Cal and SelfCal
Test Set Cal and SelfCal: Theory of Operation
Figure 3-3 Internal Transfer Standards
A SelfCal is an automatic measurement of the test set internal standards that allows
the system to remove system drift that occurs due to environmental changes such as
temperature. SelfCal allows the multiport system to recalibrate itself without having
to disconnect the DUT or connect any additional external standards or cables to the
system.
A SelfCal can be initiated manually. It is also possible to automatically perform a
SelfCal at regular, frequent time intervals. If the operating temperature of the
analyzer and test set is within the specified range (refer to Chapter 8), the
recommended time interval is about once an hour.
CAUTION Performing a Test Set Cal will effectively calibrate out the initial effects of any
external cabling and/or test fixtures. However, it must be noted that although the
SelfCal can remove drift internal to the measurement system, it cannot remove any
drift associated with cables, test fixtures and connections beyond the internal
transfer standards.
As shown in Figure 3-4, the Test Set Cal initially removes the effects of drift
associated with hardware in the area designated by arrow “A.” SelfCal can only
remove the effects of drift from the area designated by arrow “B.”