User manual

Series 3700 System Switch/Multimeter Reference Manual Section 5: Range, Digits, Rate, Bandwidth, and Filter
3700S-901-01 Rev. C / July 2008 5-7
Setting Rate from the front panel
The RATE key is used to set measurement speed from the front panel. Press
the RATE key until the desired speed message is displayed. The second line of
the display will contain the NPLC setting. Alternatively, use the NPLC option
under the function attribute menu (press CONFIG > DMM keys to display).
NOTE The Series 3700 uses internal references to calculate an accurate and
stable reading. When the NPLC setting is changed, each reference
will be automatically updated to the new NPLC setting before a
reading is generated. Therefore, frequent NPLC setting changes can
result in slower measurement speed.
Setting measurement speed from a remote interface
Use the dmm.aperture (on page 13-110) or dmm.nplc (on page 13-152)
command to set the measurement speed (integration time) over the bus.
Bandwidth
There are three bandwidth settings for ACV and ACI measurements. The RATE
setting determines the bandwidth setting as follows:
SLOW: 3Hz to 30Hz
MEDium: 30Hz to 300Hz
FAST: 300Hz to 300MHz
When the SLOW bandwidth (3Hz to 30Hz) is chosen, the signal goes through an
analog root-mean-square (RMS) converter. The output of the RMS converter
goes to a fast (1kHz) sampling A/D and the RMS value is calculated from 1200
digitized samples (1.2s).
When the MEDium bandwidth (30Hz to 300Hz) is chosen, the same circuit is
used. However, only 120 samples (120ms) are needed for an accurate
calculation because the analog RMS converter has turned most of the signal to
DC.