Multiple channels reading on SCXI 1600

[Peter K]

Hi,

I'm trying to implement reading of 64 AI channels using
SCXI-1600 and two SCXI-1100 modules.
All channels have to be read once or twice per second.
Reading will be initiated by software.

I thought this should be implemented by

DAQmxCfgImplicitTiming(TaskHandle, DAQmx_Val_OnDemand,1);

but i got the following message in this call:

--------------

ERROR: Requested value is not a supported value for this property.


Property: DAQmx_SampTimingType


You Have Requested: DAQmx_Val_Implicit


You Can Select: DAQmx_Val_SampClk, DAQmx_Val_OnDemand


Status Code: -200077

--------------

If I use another timing:

DAQmxCfgSampClkTiming(TaskHandle,'',100.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,100);

everything is fine, but sometimes I got the error:

--------------

ERROR: Attempted to read samples that are no longer available. The requested sample was previously available, but has since been overwritten.

Increasing the buffer size, reading the data more frequently, or specifying a fixed number of samples to read instead of reading all available samples might correct the problem.


Property: DAQmx_Read_RelativeTo


Corresponding Value: DAQmx_Val_CurrReadPos



Property: DAQmx_Read_Offset


Corresponding Value:



Status Code: -200279

---------------

After that task is destroyed.

How can I use Implicit Timing with acquiring readings
by software?

Thanks,
Peter.

[Erik F]

Peter,

I am a little confused, in the DAQmx C Reference Help that installs in the National Instruments->NI-DAQ folder, it lists the second input of DAQmxCfgImplicitTiming as "Sample Mode" with the options of "DAQmx_Val_FiniteSamps", "DAQmx_Val_ContSamps", and "DAQmx_Val_HWTimedSinglePoint".  Make sure you are calling the right function and passing the right type of inputs.  The C Reference help is located in the Start Menu->Programs->National Instruments->NI-DAQ folder.  Also make sure you are running the latest NI-DAQmx driver (version 7.5) available on the web.  Other than that, it sounds like since the software will be handling the sampling, you would want On Demand as your option.  Best of luck, let us know what else we can do to help.

Erik F

NI - Applications Engineer