ADLINK PCI-9524 - Manual (Page 74)

58 Operation Theory
PCI-9524 ADLINK Technology Inc.
User’s Manual Copyright 2008
4.2.8 Warm-up Requirement
PCI-9524 requires sufficient warm-up time before operation to
achieve its specified accuracy. Typically a 25-minute warm-up
time is required. Specifications are tested after 2-hour warm-up.
4.2.9 Post-processing IIR Digital Filter
Digital filter banks are provided to improve visual stability of dis-
played numbers in digital weighting or metering systems, without
the need for software-based averaging algorithms in user applica-
tions. The tap length can be programmed in ranges of 1, 2, 4, 8,
16, 32, 64, 128, 256, 512, and 1024.
Figure 4-5 illustrates several frequency response curves versus
different filter tap lengths and normalized sampling rate. Rows
from top to bottom are of tap length of 2, 16, 128 and 512. The fig-
ures in the left column have their auto-zeros disabled; those in
right column have their auto-zeros enabled, with the noise attenu-
ation response shown in dotted lines. Note the figures with auto-
zero disabled have Nyquist rates of 0.5 * fs, while those with auto-
zero enabled have Nyquist rates of 0.25 * fs. As sampling theorem
implies, keeping a source bandwidth only as large as it is neces-
sary, is a good practice to optimize noise performance.