Thank you for your questions.
For LabVIEW development, vtDAQLV.dll and vtDAOLV.dll should be used. These DLLs can be found in the software's installation directory\DAQDAOAPIs\TestDAQLabViewAndCVI.zip and TestDAOLabViewAndCVI.zip respectively. The sample codes and API document can also be found there.
The pointer to raw data array and the pointer to calibrated data array can be passed to vtDAQLV.dll through DAQLV_SetDAQData API (see figure below, refer also to Section 2.4.5 of the vtDAQ and vtDAO API document).
- API.png (63.15 KiB) Viewed 130346 times
If the calibrated data are not needed, let CalibrationMode=0 and pCalibratedData=NULL.
The raw data returned by vtDAQ API are independent from the device's internal calibration parameters such as Offset, Gain, Gain(dB), etc. The raw data can be converted to calibration data based on only two parameters:
(1) SamplingBitResolution
(2) SamplingParameters.HighLimit - SamplingParameters.LowLimit
In other words, the voltage range (HighLimit -LowLimit) will just take up the whole range allowed by the bit resolution.
Note that for 8-bit data, the data are stored in the record buffer as unsigned values; for 16-bit, 24-bit, and 32-bit data, the data are stored in the record buffer as signed values. This conforms to the data format in a wave file. Therefore it can be readily stored in a wave file without converting the data format. (refer to Section 2.1.3 of the vtDAQ and vtDAO API document).
The following C codes are what is done inside the vtDAQLV.dll to convert the raw data to calibration data.
//pd: Pointer to calibrated data array
//DAQBuffer: Pointer to raw data array
//BufferLength: Size of raw data array in bytes
void DAQBufferToChannelData(double *pd,char * DAQBuffer,unsigned long BufferLength)
{
long i,count,start;
union CH4WORD2DWORD1 {char ch[4];WORD w[2];DWORD dw;} chw1;
unsigned long nBlockAlign;
double scale1, scale2;
//transfer data from DAQ buffer to channel data
count=0;
nBlockAlign=SamplingParameters.SamplingChannels*((SamplingParameters.SamplingBitResolution+7)/8);
if(CalibrationMode==1) //interleaved
{
start=0;
}
else //channel by channel
{
start=BufferLength/nBlockAlign;
}
scale1=SamplingParameters.HighLimit[0]*2/pow(2,SamplingParameters.SamplingBitResolution);
scale2=SamplingParameters.HighLimit[1]*2/pow(2,SamplingParameters.SamplingBitResolution);
switch (SamplingParameters.SamplingChannels)
{
case 1:
switch(SamplingParameters.SamplingBitResolution)
{
case 8:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
pd[count]=(unsigned char)DAQBuffer[i];
pd[count]-=0x80;
pd[count]*=scale1;
count++;
}
break;
case 16:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
chw1.ch[0]=DAQBuffer[i];
chw1.ch[1]=DAQBuffer[i+1];
chw1.w[0]+=0x8000;
pd[count]=chw1.w[0];
pd[count]-=0x8000;
pd[count]*=scale1;
count++;
}
break;
case 24:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
chw1.ch[0]=DAQBuffer[i];
chw1.ch[1]=DAQBuffer[i+1];
chw1.ch[2]=DAQBuffer[i+2];
chw1.dw=(chw1.dw+0x800000)&0xFFFFFF;
pd[count]=chw1.dw;
pd[count]-=0x800000;
pd[count]*=scale1;
count++;
}
break;
case 32:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
chw1.ch[0]=DAQBuffer[i];
chw1.ch[1]=DAQBuffer[i+1];
chw1.ch[2]=DAQBuffer[i+2];
chw1.ch[3]=DAQBuffer[i+3];
chw1.dw+=0x80000000;
pd[count]=chw1.dw;
pd[count]-=0x80000000;
pd[count]*=scale1;
count++;
}
break;
}
break;
case 2:
switch(SamplingParameters.SamplingBitResolution)
{
case 8:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
pd[count]=(unsigned char)DAQBuffer[i];
pd[count]-=0x80;
pd[count]*=scale1;
if(CalibrationMode==1) count++;
pd[start+count]=(unsigned char)DAQBuffer[i+1];
pd[start+count]-=0x80;
pd[start+count]*=scale2;
count++;
}
break;
case 16:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
chw1.ch[0]=DAQBuffer[i];
chw1.ch[1]=DAQBuffer[i+1];
chw1.w[0]+=0x8000;
pd[count]=chw1.w[0];
pd[count]-=0x8000;
pd[count]*=scale1;
if(CalibrationMode==1) count++;
chw1.ch[0]=DAQBuffer[i+2];
chw1.ch[1]=DAQBuffer[i+3];
chw1.w[0]+=0x8000;
pd[start+count]=chw1.w[0];
pd[start+count]-=0x8000;
pd[start+count]*=scale2;
count++;
}
break;
case 24:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
chw1.ch[0]=DAQBuffer[i];
chw1.ch[1]=DAQBuffer[i+1];
chw1.ch[2]=DAQBuffer[i+2];
chw1.dw=(chw1.dw+0x800000)&0xFFFFFF;
pd[count]=chw1.dw;
pd[count]-=0x800000;
pd[count]*=scale1;
if(CalibrationMode==1) count++;
chw1.ch[0]=DAQBuffer[i+3];
chw1.ch[1]=DAQBuffer[i+4];
chw1.ch[2]=DAQBuffer[i+5];
chw1.dw=(chw1.dw+0x800000)&0xFFFFFF;
pd[start+count]=chw1.dw;
pd[start+count]-=0x800000;
pd[start+count]*=scale2;
count++;
}
break;
case 32:
for(i=0;i<BufferLength;i+=nBlockAlign)
{
chw1.ch[0]=DAQBuffer[i];
chw1.ch[1]=DAQBuffer[i+1];
chw1.ch[2]=DAQBuffer[i+2];
chw1.ch[3]=DAQBuffer[i+3];
chw1.dw+=0x80000000;
pd[count]=chw1.dw;
pd[count]-=0x80000000;
pd[count]*=scale1;
if(CalibrationMode==1) count++;
chw1.ch[0]=DAQBuffer[i+4];
chw1.ch[1]=DAQBuffer[i+5];
chw1.ch[2]=DAQBuffer[i+6];
chw1.ch[3]=DAQBuffer[i+7];
chw1.dw+=0x80000000;
pd[start+count]=chw1.dw;
pd[start+count]-=0x80000000;
pd[start+count]*=scale2;
count++;
}
break;
}
break;
}
}