Bandwidth
There are three bandwidth settings for AC volt and AC current measurements. The setting
determines the bandwidth setting as follows:
• SLOW: 3 Hz to 30 Hz
• MEDium: 30 Hz to 300 Hz
• FAST: 300 Hz to 300 MHz
When the slow bandwidth is chosen, the signal goes through an analog root-mean-square (RMS)
converter. The output of the RMS converter goes to a fast (1 kHz) sampling A/D and the RMS value
is calculated from 1200 digitized samples (1.2 s).
When the medium bandwidth is chosen, the same converter is used. However, only 120 samples
(120 ms) are needed for an accurate calculation because the analog RMS converter has turned most
of the signal to DC.
In the fast bandwidth, the output of the analog RMS converter (nearly pure DC at these frequencies)
is measured at 1 power line cycle (PLC) (16.6 ms). For remote programming, the integration rate can
be set from 0.0005 PLC to 12 PLC or 15 PLC.
To achieve the best accuracy for AC volt and AC current measurements, use the bandwidth setting
that best reflects the frequency of the input signal. For example, if the input signal is 40 Hz, a
bandwidth setting of 30 should be used.
A rate command (dmm.nplc (on page 11-209) or dmm.aperture (on page 11-145)) for AC volts and
AC current is only valid if the bandwidth for that AC function is set to 300 (300 Hz to 300 kHz).
Bandwidth is set using the dmm.detectorbandwidth (on page 11-171) remote command or the
DETECTBW menu option under the function's attribute menu.
DC voltage, DC current, and resistance measurement speed
To optimize measurement speed, select:
• dmm.autozero=dmm.OFF
• dmm.autodelay=dmm.OFF
• dmm.nplc=0.0005
• dmm.filter=dmm.OFF
• dmm.autorange=dmm.OFF
• dmm.measurecount>=1000
For resistance, assume two-wire ohm.
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