Attainable Sampling Rates when Using NI DAQmx and DIAdem DAC
Primary Software: DIAdem
Primary Software Version: 10.1
Primary Software Fixed Version: N/A
Secondary Software: DIAdem
Problem: Which Sampling Rates does DIAdem DAC Support with the NI DAQmx Driver?
Solution:
In
DIAdem DAC, you can operate
hardware that is supported by NI DAQmx drivers either in Software clock
mode or
in Hardware clock mode. Unclocked digital I/Os are the
exception, and can only be operated in the Software mode. Analog output
is also
supported only in the Software clock mode.
Hardware Clock
=============
In Hardware clock mode, the
hardware generates the clock, not DIAdem. Therefore, you only can use
clock
rates that the hardware supports. Which hardware you use with which
modules in
a measurement, may also affect the attainable clock rate. This applies
for NI
compactDAQ, for example, because with NI cDAQ, all the acquisition
modules
operate at the same clock rate. If you select a clock rate that is not
supported, the driver displays a message and recommends the next
highest clock
rate.
Software Clock
============
In the Software clock mode,
DIAdem generates the clock with the Multimedia timer on the computer
("Windows Timing"). You can set this timer to the millisecond, to a
maximum clock rate of 1kHz. DIAdem DAC uses a special algorithm to
convert
clock rates that are specified in Hz, into integer milliseconds.
Therefore,
the clock rate that
is actually attained may deviate from the clock rate specified in the
DIAdem
DAC clock block. If you want to know which sampling rate was actually
attained,
select "Measure>>Last measurement status..." in DIAdem
DAC
after the measurement, or calculate the sampling rate from the
difference
between the time values in the recorded time channel.
The
following is a list of
integer clock rates in Herz, which can be used without conversion:
in
Hz
in seconds
--------------------------------------------------------
1
1
2
0.5
4
0.25
5
0.2
8
0.125
10
0.1
20
0.05
25
0.04
40
0.025
50
0.02
100
0.01
125
0.008
200
0.005
250
0.004
500
0.002
1000
0.001
If
you want to use clock rates
that are between those in the list, we recommend that you specify the
clock
rate in the DIAdem DAC clock block in milliseconds between 1 and 1000.
You then
no longer need to convert the values, and the time channel has values
with only
a few decimal places. For example, if you enter 3 milliseconds, which
corresponds to 333.33...Hz, you get a time channel that increments in
steps of
0.003 seconds.
Related Links:
Attachments:
Report Date: 12/19/2006
Last Updated: 12/19/2006
Document ID: 44I6E4FN
