ADLINK PCI-9524 - Manual (Page 64)

48 Operation Theory
PCI-9524 ADLINK Technology Inc.
User’s Manual Copyright 2008
4.2 Analog Input Channels
The following sub-sections depict the internal operations of signal
amplification, conversion, post-processing, and calibration.
4.2.1 Signal Acquisition and Processing Flow
PCI-9524 was designed to detect weak signals through proper sig-
nal conditioning, amplification and digital post filtering, as
depicted.
Figure 4-2: Signal acquisition and data processing flow
for transducer input channels
At the first stage, the voltage excitation applied to the load-cell
transducer transforms the resistive change into an electric signal,
in the range of tens of milli-volts. Before entering amplification
stage, the signal passes through a passive filter stage to filter out
unwanted interference. A custom-made, low temperature coeffi-
cient instrumentation amplifier provides a fixed gain of 25, and the
necessary level-shift (1). The amplified signal is fed into a sigma-
delta modulator running at 1.92 MHz, pushing the in-band quanti-
zation noise to a higher frequency, and filtering most of which out
using a 5-order SINC filter. The filtered digital data passes through
an averager to tune down the data rate to a specific sampling rate.
A built-in correction algorithm automatically calibrates the output
data, which can then be pushed into the on-board FIFO for data
transfer to PC memory, or sent to the next DSP stage described
below.