Hello. I'm using the ANSI C library and have two cards: an NI 9237 and an NI 9401. The NI 9237 has a load cell, the NI 9401 has a linear encoder. I need to record the load and position channels in perfect synchrony. To that end, I adapted the following from an example. I configure the two channels, tie them both to the SampleClock of the analog card. The analog card task gets used to register the EveryNSamples event. The task, and I get the callbacks. But, while I always get the 1000 rows of data from both read functions, the data is not aligned in time. The position data is "ahead" of the load data. I feel like I must be missing a step syncing the data, but I can't find anything in any example where this shouldn't work.
Thanks in advance for any insight.
samplesPerSec_ = 10000; // 10khz
DAQmxErrChk(DAQmxCreateTask("AnalogInputTask", &taskHandle));
DAQmxErrChk(DAQmxCreateTask("EncoderTask", &encoderTask));
taskHandles_.push_back(taskHandle);
taskHandles_.push_back(encoderTask);
DAQmxErrChk(DAQmxCreateAIForceBridgeTwoPointLinChan(
taskHandle,
"cDAQ9185-1E26063Mod1/ai0",
"Load",
-2224.1108,
2224.1108,
DAQmx_Val_Newtons,
DAQmx_Val_FullBridge,
DAQmx_Val_External,
10.0,
350,
0,
2.3222,
DAQmx_Val_mVoltsPerVolt,
0,
2224.1108,
DAQmx_Val_Newtons,
NULL
));
DAQmxErrChk(DAQmxCreateCILinEncoderChan(
encoderTask,
"cDAQ9185-1E26063Mod3/ctr0",
"Position",
DAQmx_Val_X4,
1,
0.0,
DAQmx_Val_AHighBHigh,
DAQmx_Val_Meters,
0.0000039976,
0.0,
NULL
));
DAQmxErrChk(DAQmxCfgSampClkTiming(
taskHandle,
"/cDAQ9185-1E26063Mod1/ai/SampleClock",
samplesPerSec_,
DAQmx_Val_Rising,
DAQmx_Val_ContSamps,
1000
));
DAQmxErrChk(GetTerminalNameWithDevPrefix(taskHandle, "ai/SampleClock", trigName));
DAQmxErrChk(DAQmxCfgSampClkTiming(
encoderTask,
"/cDAQ9185-1E26063Mod1/ai/SampleClock",
samplesPerSec_,
DAQmx_Val_Rising,
DAQmx_Val_ContSamps,
1000
));
DAQmxErrChk(DAQmxRegisterEveryNSamplesEvent(
taskHandles_[0],
DAQmx_Val_Acquired_Into_Buffer,
1000,
0,
EveryNCallback,
(void*)this
));
static int32 CVICALLBACK EveryNTest(
TaskHandle taskHandle,
int32 everyNsamplesEventType,
uInt32 nSamples,
void* callbackData
)
{
DAQmxErrChk(DAQmxReadAnalogF64(
taskHandles_[0],
1000, // the number of samples to read
10.0,
DAQmx_Val_GroupByScanNumber,
analogDataBuffer_.data(),
analogDataBuffer_.size(), // the available size of the buffer
&analogRead,
NULL
));
DAQmxErrChk(DAQmxReadCounterF64Ex(
taskHandles_[1],
1000,
10.0,
DAQmx_Val_GroupByScanNumber,
counterDataBuffer_.data(),
counterDataBuffer_.size(),
&counterRead,
NULL
));
.. push data into FIFO queue ..
}
