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2-14
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Chapter 2
Using the Module
decoupling means that the full bandwidth of the demodulator is always available to the sampling
system. Therefore, caution must be taken so the core displacement frequency does not exceed
the Nyquist frequency. Otherwise, high frequency components of the displacement may become
aliased.
Figure 2-9 shows the HWTSP data path model.
Figure 2-9.
HWTSP Data Path Model
The ADC samples the input stream, which is then processed by the demodulator. The
demodulated signal is then routed to the sampling system, which returns the sample to the
PXI Express controller or computer based on the Sample Clock signal.
Maximum HWTSP Rate Analysis
During HWTSP acquisitions the maximum achievable acquisition rate without missing a sample
is affected by both the transfer and application time. Refer to Figure 2-10.
Note
HWTSP acquisitions can detect if they cannot keep up with the acquisition
rate. Refer to the
Hardware-Timed Single Point Sample Mode
topic in the
NI-DAQmx
Help
for more information.
Figure 2-10.
Transfer Time and Application Time Relationship
PXI Expre
ss
Controller
or Comp
u
ter
An
a
log Front End
ADC
Demod
u
l
a
tor
HWT
S
P
Sa
mpler
Rate
MAX
1
TransferTime
ApplicationTime
+
------------------------------------------------------------------------------------------------
=
Tr
a
n
s
fer
Next
Sa
mple L
a
tency
Applic
a
tion Time
20
µ
s
*
561.02
µ
s
**
N
Sa
mple
Clock
Sa
mple
Clock
Ac
qu
i
s
ition R
a
te Period
W
a
it Time (Idle)
*Tr
a
n
s
fer time m
a
y v
a
ry depending on
s
y
s
tem.
**561.02
µ
s
i
s
the
a
pproxim
a
te l
a
tency for excit
a
tion fre
qu
encie
s
b
etween 5 kHz
a
nd 10 kHz.