Bandwidth; Filter - Keithley 3700 series Reference Manual

Section 4: Range, Digits, Rate, Bandwidth, and Filter

Bandwidth

There are three bandwidth settings for ACV and ACI measurements. The RATE setting
determines the bandwidth setting as follows:
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When the SLOW bandwidth (3Hz to 30Hz) is chosen, the signal goes through an analog 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.
In the FAST bandwidth (300Hz to 300kHz), the output of the analog RMS converter (nearly pure
DC at these frequencies) is simply measured at 1 PLC (16.6ms). For remote programming, the
integration rate can be set from 0.0005PLC to 12PLC or 15PLC.
To achieve the best accuracy for ACV and ACI measurements, use the bandwidth setting that
best reflects the frequency of the input signal. For example, if the input signal is 40Hz, then a
bandwidth setting of 30 should be used.
NOTE

Filter

The digital filter is used to stabilize noisy measurements. The displayed, stored, or transmitted
reading is a windowed-average of a number of reading conversions (from 1 to 100).
The filter setup is ―remembered‖ and can be unique for each measurement function (DCV, ACV,
DCI, ACI, Ω2, Ω4, CSΩ, and TEMP). When you select a function, the instrument will return to
the last filter setup for that function.
NOTE
4-6
SLOW: 3Hz to 30Hz
MEDium: 30Hz to 300Hz
FAST: 300Hz to 300MHz
A rate command (dmm.nplc
and ACI is only valid if the bandwidth for that AC function is set to 300 (300Hz to
300kHz). Bandwidth is set using the dmm.detectorbandwidth ICL command or
DETECTBW menu option under the function's attribute menu).
The various instrument operations, including Filter, are performed on the input signal
in a sequential manner
Series 3700 System Switch/Multimeter Reference Manual
(on page 9-105) or dmm.aperture
Document Number: 3700S-901-01 Rev. A / August 2007
(on page 9-70)) for ACV