Hi bman
The NIDAQ User's manual for PC compatibles v 6.7 states on page 3-32
Multirate Scanning
Use multirate scanning to scan multiple channels at different scan rates
and acquire the minimum amount of data necessary for your application.
This is particularly useful if you are scanning very fast and want to write
your data to disk, or if you are acquiring large amounts of data and want to
keep your buffer size to a minimum.
Multirate scanning works by scanning each channel at a rate that is a
fraction of the specified scan rate. For example, if you want to scan four
channels at 6,000, 4,000, 3,000, and 1,000 scans per second, specify a scan
rate of 12,000 scans per second and a scan rate divisor vector of 2, 3, 4,
and 12.
This is quite similar to what you wrote, but apparently allows me to read
directly without manually deleting aquired points, which is what I surmise
from your explanation. the texto goes onto say:
NI-DAQ includes three functions for multirate scanning:
.. SCAN_Sequence_Setup
.. SCAN_Sequence_Retrieve
.. SCAN_Sequence_Demux
Use SCAN_Sequence_Setup to identify the channels to scan, their
gains, and their scan rate divisors. After the data is acquired, use
SCAN_Sequence_Retrieve and SCAN_Sequence_Demux to arrange
the data into a more convenient format.
How do I call these functions from CVI?
Many thanks for your help.
LVilla
"bman" wrote in message
news:50650000000500000033410000-999158726000@exchange.ni.com...
> LVilla
>
> Currently you cannot scan multiple channels at different rates.
>
> However, you can simulate this by scanning the data at the fastest
> rate you will need, to be an integer multiple of all of your scan
> rates, and then decimating, to get rid of the extra data.
>
> E.g.. If the sample rates you want are:
> 2Hz, 4Hz, 3Hz;
> Then the required sample rate would be 12Hz.
> The sample decimation you will need to do is:
> Every 6th point for 2Hz,
> Every 3th point for 4Hz,
> Every 4th point for 3Hz,
>
> Of course this will only work if the required sample rate is within
> the range of DAQ card. If it isn't then you can sample at the nearest
> sample rate that can accommodate most of your wanted sample rate and
> then interpolate (curve fit) the data from the other
> channels and resample from the interpolation.
>
> I hope this helps.
>
> Brian
