DAQ aquiring data needs too much time

[Hillu]

Hello,

I'm using two PCI-6013 DAQ boards under Windows 2000 prof., CVI 6.0 and NI-DAQ 6.9.3f. If I start a measurement of 15000 points from one DAQ card with a sample rate of 20000 pts/s I expect that the measurement will be finished in about 750 ms. But the first measurement always needs 900 ms, all further measurements need about 850 ms. Here is the corresponding part of my code:

// start measurement
iState = DAQ_Start((i16)GetDevAdrEntry(pDAQDevice),
(i16)uiChannel,
-1,
iBinaryData,
uiNumSamplePts,
iSampleTimebase,
(u16)iSampleIntervall);

if(iState)
{
//
error
} // endif

// wait for end of measurement
dwStartTime = GetTickCount();
while(1)
{
if(!(iState = DAQ_Check(GetDevAdrEntry(pDAQDevice),
&iDAQReady,
&uiNumReadSamples)))
{
if(iDAQReady && uiNumReadSamples == uiNumSamplePts)
{
dwEndTime = GetTickCount();
break;
} // endif
} // endif

if((GetTickCount() - dwStartTime) > (MEAS_TIMEOUT * 1000))
{
DAQ_Clear(GetDevAdrEntry(pDAQDevice));
LocalFree(iBinaryData);
LocalFree(fVoltageData);
*fMeasValue = -99.0;
return(0);
} // endif
} // endwhile

Thanks for help,

Hillu

[ThomasD]

Hello,

the 750ms you expect are the real measurement time. It want be not possible to reach this time. The first measurement time is always a little longer than the following times. The cause is that CVI has to open the .dll in this step. This effect will be seen by all the other c-based programms too.
If you measure the signal continuously, it will be possible to get smaller measurement times.

Regards
Thomas D.
NI Germany
(SRQ 198373)