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7:
Step
Add known poles and zeros (Optional)
Edit the curve-fit table to add known poles or zeros. For example, if a continuous system contains
an integrator, add a pole at 0 Hz. Fixed terms are indicated by an arrow. Line numbers must be
used explicitly to delete these. See the previous description of the EDIT TABLE softkey for
additional details.
N ote
When transferring a synthesis table to the curve-fit table, all terms are fixed. Fitting
to any table when all terms are fixed is a null fit. This is due to the process of
removing frxed terms from the transfer function: a transfer function for only the
fixed terms is generated, and then divided out of the frequency response in trace
(done internally, so that trace
function is performed. Fixing all terms leaves the reduced function as a constant.
Thus, the original table is simply returned. The idea of f ixing terms is to f IX only
some of the terms believed to be in a partially unknown transfer function.
Step 8: Enter any known delays (Optional)
Enter any known delays with the TIME DELAY softkey. To do this, press CURVE FIT followed by
EDIT TABLE, TABLE FCTNS, and TIME DELAY. Then enter the time delay. See the description of
the TIME DELAY softkey in "The TABLE FCTNS Menu" for additional details.
This should be done if a phase ramp exists in the frequency response in the s domain. This should
also be done if a partial sample delay has imposed a phase ramp in the frequency response in the z
is
domain (a phase ramp
·n
Z
•
Step 9: Specify the Weighting Function (Optional)
The value of any portion of the curve can be specified by first identifying it with WEIGHT REGION,
and then entering the value with WEIGHT VALUE. You can enter values between 0.0 and 1.0.
A
non-periodic, and if caused by a partial sample delay, cannot be modeled as
is unaffected). Then a fit to the reduced transfer
Curve Fit
Curve Fit Setup Steps
A
16-43
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