Figure 4-9: Waveform Crest Factor Affects Max. Rms Voltage - Ametek California Instruments MX15 Series User Manual

The MX Series power source automatically limits the maximum allowable programmed rms
voltage of 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 1Pi controller will prevent the user from programming the rms voltage
above this limit. If a value is entered in the PROGRAM menu above this value, a "Voltage peak
error" message is generated.
The figure shown here illustrates the relationship between the crest factor of the wave shape (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 sine wave 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 MX Series is used over the bus, the ":VOLT? MAX" query command 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.
4.4.5 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 1Pi controller automatically applies a band-pass filter to all custom waveforms
as they are downloaded. The controller implements the following process for user defined
waveforms:
Each downloaded waveform will have a computed frequency limit that is less than or equal the
maximum frequency limit of the AC source. The frequency limit is a function of the harmonics
content of the waveform and will follow the equation below.
If Fmaxh is below the minimum frequency limit, the waveform will be rejected at download time
and the label will be deleted from the waveform catalogue.
If the MX Series is used over the bus, the ":FREQ? MAX" query command can be used to
determine the maximum allowable fundamental frequency for the selected waveform. Using the
returned value as part of a program will prevent range errors.
Limits assume a program of full-scale voltage. No adjustments for voltage setting are made
below the full-scale value.
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Figure 4-9: Waveform Crest Factor Affects Max. rms Voltage

Fmax
h
= Fmax/(level * h )
n