NIDAQ

[C2PO]

Hi everyone - I am using NIDAQ-mx with C++ and a NI USB-6341.  I am looking to use a lowpass filter on the analog ins but don't know if this is possible.  

The problem is this code gets hung up when I try to use the filter. 

This is what I'm doing:

if( !( retVal = DAQmxCreateTask( "", &config->taskHandle ) ))

if( !( retVal = DAQmxCreateAIVoltageChan( config->taskHandle, ss.str(), "", DAQmx_Val_RSE,
config->minVoltage, config->maxVoltage, DAQmx_Val_Volts, NULL ) ) )

if( !( retVal = DAQmxSetAILowpassEnable(config->taskHandle, "", 1) ) ) 
if( !( retVal = DAQmxSetAILowpassCutoffFreq(config->taskHandle, ss.str(), 500) ) )

if( !( retVal = DAQmxCfgSampClkTiming( config->taskHandle, NULL, config->frequency,
DAQmx_Val_Rising, DAQmx_Val_ContSamps, numSamplesPerChannel ) ) )

Is this the correct way to do this.  Do I create the task, then the AIchannel, then the filter, then the cutoff freq, then the timing?

Any help would be much appreciated.

Thanks!

[Ryan-C]

Hi C2PO,

It seems you are doing things in the correct order (specifically addressing your final question of the post).

There are many examples that I hope were installed on your computer when you instaleld NI-DAQmx.  These would be located under the Start Menu in Windows > All Programs > National Instruments | NI-DAQ > Text-Based Code Support > ANSI-C Examples.  Here, one that I thought applied particularly well to your situation was in \NI-DAQ\Examples\DAQmx ANSI C\Analog In\Measure Voltage\Cont Acq -Int Clk-Cfg Filt-SCXI 114x

The applicable code here looks like:

    DAQmxErrChk (DAQmxCreateTask("",&taskHandle));
    DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev1/ai0","",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));
    DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandle,"",1000.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,1000));
    DAQmxErrChk (DAQmxSetAILowpassEnable(taskHandle,"",1));
    DAQmxErrChk (DAQmxSetAILowpassCutoffFreq(taskHandle,"",cutoffFreq));
    DAQmxErrChk (DAQmxGetAILowpassCutoffFreq(taskHandle,"",&cutoffFreq));

Note: If these examples have not been installed on your computer, doing a repair of your DAQmx may fix this.

Best of luck,

[Brad_K · Accepted solution]

Hi C2PO,

The DAQmx lowpass filter properties are for devices that have configurable lowpass filter hardware, like the NI 628x, NI PXIe-4300, some NI 61xx devices, and some SCXI modules. The NI 6341 doesn't have a configurable lowpass filter.

However, the code shouldn't hang in this case, it should return an error. Did you leave out the body of each if-statement in your post, or is this a deep set of nested if-statements? Either way, the example programs that Ryan C posted should help with the error handling.

Brad

[C2PO]

Thanks Ryan and Brad for the replies - I'm doing a :

retVal = DAQmxSetAILowpassEnable(config->taskHandle, ss.str(), 1)

which throws the exception below for error  -200077

throw exception(errorBuffer);//why this hangs in my application

but I get through that errror with:

retVal = DAQmxSetAILowpassEnable(config->taskHandle, ss.str(), 0)

but then I get errors like -200452 and "specifed property is not supported by the device etc." 

So it now makes sense that this won't work on the NI 6341.

Thanks again.