What is the correct channel name

[chaomi0127]

Hello,

I'm using text based API and a NI 9201. I'm trying to get voltage samples. I found that the DAQmxReadAnalogF64() function always takes a lot of time. So I did a bit of research and decided to use function DAQmxSetAIADCTimingMode(). 

However, I don't know the name of the channel. The name of the chassis is "NI-DAQ". There are 4 C modules. The name of the physical channel for the measurement is "NI-DAQMod4/ai0". 

I called function like this error |= DAQmxSetAIADCTimingMode(*task, "NI-DAQMod4\ai0", DAQmx_Val_HighSpeed);


But I the status bit returns an error. What is the correct channel name?

[chaomi0127]

Just add more information, calling DAQmxSetAIADCTimingMode() with NI 9201, returns status -200458. It seems NI 9201 does not support this API. What are my options to improve execution time of DAQmxReadAnalogF64()?

[santo_13]

It is difficult to help/guide without seeing what you've created and how instruments appear in your NI MAX. As a starting point, please share the code that you created and a snippet of how your C-series modules appear in NI MAX.

On the other hand, have you looked at the examples that ship with DAQmx drivers?

[chaomi0127]

I'm on Linux, so I cannot use NI MAX. 

Using command nilsdev, there is one NI DAQ chassis with 4 DAQmx C modules.
NI-DAQ
NI-DAQMod4
NI-DAQMod3
NI-DAQMod1
NI-DAQMod2

I'm using NI-DAQMod4, which is a NI 9201 to measure analog input of voltage.

The code is below:

error = DAQmxCreateTask("", task);

// value of 'chan' is "NI-DAQMod4/ai0".
error |= DAQmxCreateAIVoltageChan(*task, chan, "", DAQmx_Val_Cfg_Default, 0.0, 5.0, DAQmx_Val_Volts, NULL);

// value of 'buf' is "".
// value of 'KDAQNI::config.rate_ms' is 25. 
error = DAQmxCfgSampClkTiming(*task, buf, (1000.0 / (float64)KDAQNI::config.rate_ms), DAQmx_Val_Rising, DAQmx_Val_ContSamps, 1);

 
There is a thread running which read the analog input:

while (KDAQ_TASK_STATE_RUNNING == io->state)
    {
        result = DAQmxReadAnalogF64(io->task, 1, 0.025, 
             DAQmx_Val_GroupByChannel, values, 1, &samples, NULL);

        // Handle errors
        if (result < 0)
        {
            LOG_DEBUG(LOG_KDAQ, "AI failed read within 0.5s [result=%d]", 
                 result);
        }
        else
        {
            for (i=0; i<num_io; i++)
            {
                *io->io[i].register_ptr = ((float64)io->io[i].scale_factor) * 
                    (values[i] - (float64)io->io[i].offset);
            }
        }
    }

DAQmxReadAnalogF64(io->task, 1, 0.025,
DAQmx_Val_GroupByChannel, values, 1, &samples, NULL) function takes long time to run, about 15 - 25 ms.

[chaomi0127]

Update: I'm measuring a counter input and an analog input at the same time. Counter input is measured using a NI 9421. Analog input is measured using a NI 9201. 

After some experiments, DAQmxReadAnalogF64() function is also interfering the counter input measurement.

Without DAQmxReadAnalogF64() function, counter input measurement is good and accurate. 

But with DAQmxReadAnalogF64() function running in a thread every 25ms, counter input measurement is wrong and very inconsistent. 

I understand that DAQmxReadAnalogF64() is a blocking function, but I do not expect it interfering with other measurements.