I need to continuously acquire data from daqmx card, write into a file and at the same time corelate (in terms of time) the data with signals from other instruments. The current problem is that there is time delay during read and write data into buffer,thus causing misalignment of the data from multiple instruments. Is there a way to solve the delay? or Is there a way to mark the time of the data acquisition in the buffer? If I know the starting time (e.g. 0) of data acquisition and sampling rate (e.g. 1kHz), can I simply add 1ms to each data sample in the buffer? The current code is shown below.
void DataCollectionWin::ConnectDAQ()
{
DAQmxErrChk(DAQmxCreateTask ("", &taskHandle));
DAQmxErrChk(DAQmxCreateAIVoltageChan(taskHandle,"Dev1/ai0,Dev1/ai1,Dev1/ai2,Dev1/ai3,Dev1/ai4,Dev1/ai5,Dev1/ai16,Dev1/ai17,Dev1/ai18,Dev1/ai19,Dev1/ai20,Dev1/ai21,Dev1/ai6,Dev1/ai7,Dev1/ai22","",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk(DAQmxCfgSampClkTiming(taskHandle,"",1000.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,60000));
DAQmxErrChk (DAQmxRegisterEveryNSamplesEvent(taskHandle,DAQmx_Val_Acquired_Into_Buffer,50,0,EveryNCallback,NULL));// Every 50 samples the EveryNSamplesEvent will be trigured, to reduce time delay.
DAQmxErrChk (DAQmxRegisterDoneEvent(taskHandle,0,DoneCallback,NULL));
DAQmxErrChk (DAQmxStartTask(taskHandle));
......
}
int32 CVICALLBACK EveryNCallback(TaskHandle taskHandle, int32 everyNsamplesEventType, uInt32 nSamples, void *callbackData)
{
DAQmxErrChk (DAQmxReadAnalogF64(taskHandle,50,10.0,DAQmx_Val_GroupByScanNumber,data,50*15,&read,NULL));
//memcpy(l_data,data,6000);
SetEvent(hEvent);
l_usstatus_e[0]=g_usstatus[0];// signals from other instruments that need to be corelated with the data from daq cards.
l_optstatus_e[0]=g_optstatus[0];
if( read>0 ) // write data into file
{
//indicator=1;
for (i=0;i<read;i++)
{ //fprintf(datafile,"%d\t",i);
fprintf(datafile,"%c\t",l_usstatus_s[0]);
fprintf(datafile,"%c\t",l_usstatus_e[0]);
fprintf(datafile,"%c\t",l_optstatus_s[0]);
fprintf(datafile,"%c\t",l_optstatus_e[0]);
fprintf(datafile,"%.2f\t",data[15*i]);
// sprintf( pszTemp, "%f", data[6*i]);
// pListCtrl->SetItemText(0, 2, pszTemp);
//pWnd->m_trackinglist.SetItemText(0, 2, pszTemp);
fprintf(datafile,"%.2f\t",data[15*i+1]);
fprintf(datafile,"%.2f\t",data[15*i+2]);
.......
}
