XT2640 Operating Manual
13 July 2016
Page 43 of 187
Recommendations:
The AUTO‐TRACK selection is recommended for most applications unless a set bandwidth or no limit at all is specifically
required by the application or if measuring frequencies close to or above the maximum measurable frequency of the
channels.
Note:
If the bandwidth restriction is beyond the capabilities of a channel then no bandwidth limitation is applied.
If you select AUTO‐TRACK then you can return to this screen and see the actually applied limit, which is displayed in the
lower half of this button, e.g. AUTO (6k).
If you also select NONE as the FUND setting, then a fixed 500Hz bandwidth limitation is used.
See section 16 for full details regarding configuring this for measurements on PWM generated signals.
12.4.2.2.4
Configuring
Harmonic
Analysis
The HARMONICS button allows you to select the maximum number of harmonics to analyze within the VPA being configured if MEAS
MODE is not EN61000‐3‐2 or EN61000‐3‐12. This is not available when MEAS MODE is set to SPECTRUM or if FUND is set to NONE.
Recommendations:
For most applications this should be set to 50 unless harmonic analysis is not required in which case it should be set to 0.
Only if the specific application requires more harmonics is it recommended to set this higher.
In modulated signal applications (such as motor drives) this should be a low value and often a figure of 5 or less is used.
Notes:
If this is set to 0 then no harmonics will be analyzed in the VPA being configured.
Lead/lag and all non‐harmonic measurements are still available when not performing harmonic analysis.
In order to accurately measure very high‐order harmonics the cycle‐to‐cycle jitter of the signal frequency is of importance.
To accurately measure 500 harmonics this requires that the source have <0.025% frequency jitter. Mains supplies rarely
achieve this. If it is desired to measure high‐order harmonics of an unstable frequency source then it is recommended that
you consider using spectrum analysis instead.
The actual number of available harmonics is limited to half the bandwidth limitation, and may be further limited by other
settings and/or by the measured fundamental frequency.
See section 16 for full details regarding configuring this for measurements on PWM generated signals.
12.4.2.2.5
Configuring
Spectrum
Analysis
The SPECTRUM button (not shown in the example screen above) allows you to enter the desired frequency resolution (in Hz) and
maximum desired frequency (in Hz) for the spectrum analysis. This is only available when MEAS MODE is set to SPECTRUM.
Note:
These settings have a major effect on the speed at which spectrum measurements can be made, for best speed use the
largest possible frequency resolution and the smallest possible ratio between the resolution and maximum frequencies.
The frequency resolution entry is limited to be within 0.01Hz to 1kHz
The maximum frequency entry is limited to between 100 and 16384 times the frequency resolution.
12.4.2.3
CONFIGURING
HOW
MEASUREMENT
RESULTS
ARE
DISPLAYED
This is performed by using the buttons in the DATA area. Depending on configuration and the installed channels some buttons may
not be present or may not allow modification of the setting.
12.4.2.3.1
Setting
the
Default
Coupling
for
Data
The COUPLING button allows you to select whether DC ONLY, AC ONLY or AC+DC results will be shown as the primary data on the
POWER DATA screens, and used for the calculation of integrated data, and used for obtaining total values for the selected VPA.
Recommendation:
Unless it is known that only the DC results are required then the AC+DC setting is recommended.
Note:
DC ONLY is not available if MEAS MODE is EN61000‐3‐2 or EN61000‐3‐12.
This does not restrict channel measurement data to the selected coupling; the measurement results within a channel are
always available for all couplings.
12.4.2.3.2
Setting
for
Result
Averaging
The RESPONSE button allows you to select that measurement results will be averaged over time if MEAS MODE is not EN61000‐3‐2
or EN61000‐3‐12.
Settings of FASTEST, MEDIUM, SLOW and SLOWEST are available.
Recommendation:
The performance and specifications of the XT2640 are not reliant on the use of this capability; it should be used when
needed and otherwise set to FASTEST.
When using results which are dependent on results from multiple VPAs or from motor results then these results may not
all be using the same response averaging, which may result in inappropriate results while the signals are changing. In
these cases it is recommended to use FASTEST for all response averaging settings.
Note:
