HP 8753E User Manual page 664

Two additional categories of measurement errors are connection techniques and contact
surfaces.
The connection techniques category includes torque limits, flush setting of sliding load center
conductors, and handling procedures for beadless airlines.
The contact surfaces category includes cleaning procedures, scratches, worn plating, and rough
seating.
These types of errors are not accounted for in the uncertainty analysis.
Measurement Uncertainty Equations
Any measurement result is the vector sum of the actual test device response plus all error
terms, The precise effect of each error term depends on its magnitude and phase relationship
to the actual test device response. When the phase of an error response is not known, phase
is assumed to be worst case (-HO0 to + BOO). Random errors such as noise and connector
repeatability are generally combined in a root-sum-of-the-squares (RSS) manner.
An analysis of the error model in Figure El yields an equation for the reflection magnitude
uncertainty. The equation contains all of the llrst order terms and the significant second order
terms The terms under the radical are random in character and are combined on an RSS basis.
The terms in the systematic error group are combined on a worst case basis. In all cases, the
error terms and the S-parameters are treated as linear absolute magnitudes.
Reflection magnitude uncertainty (forward direction) =
Erm = Systematic + d(Random)2 + (Drift and Stability)2
Systematic = Efd + Efr Sll + Efs S112 +
Rr = d(Crrl + 2CrtlSll + CrrlS112)2 + (Crr2S21S12)2
Random = am + (RT-)~ + (NT)~
Nr = d(EfntSll)z + Efnf2
Drift and Stability = Dmlbl
Determining System Measurement Unwrtainties B-3