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User Manual
i Series / iX Series 81
4.4.5 RMS Amplitude Restrictions
The output of a sinewave may be programmed to the full rms value of the voltage range
selected. If the AC source is in the 300 V range, the maximum programmable rms voltage is 300
Volt. If a custom waveform is used however, the maximum programmable rms voltage may be
less than the maximum range value. The voltage range limit is based on the use of a sinewave
with a 1.414 crest factor. A 300 V rms sinewave has a 424 Volt peak voltage. The AC source has
a maximum peak voltage capability that is determined by the selected voltage range. If the user
selects a custom waveform with a crest factor that is higher than 1.414, the peak voltage would
exceed this maximum if the rms voltage were to be programmed at 300 V rms.
The iX Series automatically limits the maximum allowable programmed rms voltage of a any
custom waveform by calculating the crest factor of the selected waveform and controlling the rms
limit accordingly. Thus, each custom waveform may have a different maximum rms value. The iX
controller will prevent the user from programming the rms voltage above this limit. If a value is
entered in the
PROGRAM 1 menu above this value, a “Voltage peak error” message is
generated.
Figure 4-31: Waveform crest factor affects max. rms voltage
The figure shown here illustrates the relationship between the crest factor of the waveshape (or
its “peakiness”) and the maximum peak voltage allowed for a given voltage range. Since the
peak voltage cannot exceed the AC source‟s capabilities, the programmable rms voltage has to
be restricted, in this case to only 167.8785 volt for the waveform on the left. The sinewave on the
right can be programmed to the full 300 V rms as this still falls within the same peak voltage
limitation of the AC source.
If the iX Series is used through the bus, the :VOLT? MAX query can be used to determine the
maximum allowable rms voltage for the selected waveform. Using the returned value as part of a
program will prevent range errors.
4.4.6 Frequency Response Restrictions
The user may create a waveform that contains any number of harmonic frequencies of the
fundamental. The AC Source itself however has a finite signal bandwidth and will attenuate
higher frequency components of the signal. To limit the maximum frequency component of the
output signal, the iX controller automatically applies a band-pass filter to all custom waveforms
as they are downloaded. This will limit the signal bandwidth to no more than 50 times the
fundamental frequency. Consequently, very fast transients embedded in the user provided
waveform data points may be modified as part of the download process. The frequency domain
VIEW mode in the WAVEFORMS menu may be used to visualize the content of each custom
waveform register on the LCD.