1GA16_1L.DOC ROHDE & SCHWARZ15
The open-circuit generator voltage V
q
being known, the following voltage ratio is obtained:
U
q
/ Z+R = U
1
/ Z
Because of the complex impedance, the equation cannot be solved for Z, but the generator may be used
as a current source for Z << R
I
q
= U
q
/ R
so that the following applies:
Z = U
1
/ I
q
For impedances in loudspeakers, the condition Z << R is fulfilled if a generator with a source impedance
of 600 is selected. Since this source impedance is only available at the XLR outputs, the BAL outputs
have to be used.
If the value for
I
q
= U
q
/ 600
is entered as reference value for the RMS or DC measurement and V/Vr is selected for the display, the
measured value for Z can be directly read off in .
5.1.2 Special Notes on Entry of Parameters
With the aid of the RUNAWAYS softkey (F9, level 3) it can be determined how many outliers (runaways)
are tolerated by the algorithm for extreme value determination (resonance and tuning frequency).
In this case the relative maximum or minimum values have to be determined. For instance, when
searching for the maximum it may happen (particularly with very flat impedance curves) that a lower value
is measured although the curve slightly rises. To avoid misinterpretations, the algorithm responds only if
the following N RUNAWAYS show a decrease.
N is recommended to have a value of 2. Higher values extend the search time and may even mask
runaways. In the case of frequency sweeps lower values may be sufficient (even 0) but this has to be
determined empirically.
Under the REF SPK softkey the GO/NOGO test mode can be switched on and off, the trace of the
reference unit loaded and tolerances entered. With this softkey, OFF (no GO/NOGO test), TRACE A
(GO/NOGO test only) or TRACE B (impedance curve on trace A, GO/NOGO test on trace B) can be
selected.
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