User manual

Section 5: Range, Digits, Rate, Bandwidth, and Filter Series 3700 System Switch/Multimeter Reference Manual

5-8 3700S-901-01 Rev. C / July 2008

In the FAST bandwidth (300Hz to 300kHz), the output of the analog RMS

converter (nearly pure DC at these frequencies) is 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 A rate command (dmm.nplc (on page 13-152) or dmm.aperture (on

page 13-110)) for ACV 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 (on page 13-132) ICL command or

the DETECTBW menu option under the function's attribute menu).

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 retained 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 The various instrument operations, including Filter, are performed on

the input signal in a specific, predetermined order. For example, if

both REL and MXB (a math operation) are enabled, the REL

operation will always be performed before MXB.

Filter characteristics

In general, the digital filter places a specified number of A/D conversions ("Filter

Count") into a memory stack. These A/D conversions must occur consecutively

within a selected reading window ("Filter Window"). The readings in the stack

are then averaged to yield a single filtered reading. The stack can be filled using

the moving or repeating average filters. Details about digital filter characteristics

are provided in the following paragraphs.

Digital filter types

There are two digital filter types: moving and repeating.