c - NI USB 6211 读取模拟电压输入

Question

我正在尝试通过 C 程序读取输入到 NI USB-6211 的电压。为此，我尝试使用安装程序附带的一些示例程序，但无济于事。我已经查看了文档，但说实话，它根本没有多大帮助。

这是我改编的代码。 (它有一些错误检查，并且还要求输入...)

/*********************************************************************
*
* ANSI C Example program:
*    Acq-IntClk.c
*
* Example Category:
*    AI
*
* Description:
*    This example demonstrates how to acquire a finite amount of data
*    using the DAQ device's internal clock.
*
* Instructions for Running:
*    1. Select the physical channel to correspond to where your
*       signal is input on the DAQ device.
*    2. Enter the minimum and maximum voltages.
*    Note: For better accuracy try to match the input range to the
*          expected voltage level of the measured signal.
*    3. Select the number of samples to acquire.
*    4. Set the rate of the acquisition.
*    Note: The rate should be AT LEAST twice as fast as the maximum
*          frequency component of the signal being acquired.
*
* Steps:
*    1. Create a task.
*    2. Create an analog input voltage channel.
*    3. Set the rate for the sample clock. Additionally, define the
*       sample mode to be finite and set the number of samples to be
*       acquired per channel.
*    4. Call the Start function to start the acquisition.
*    5. Read all of the waveform data.
*    6. Call the Clear Task function to clear the task.
*    7. Display an error if any.
*
* I/O Connections Overview:
*    Make sure your signal input terminal matches the Physical
*    Channel I/O Control. For further connection information, refer
*    to your hardware reference manual.
*
*********************************************************************/

#include <stdio.h>
#include <NIDAQmx.h>
#include <string.h>

#define DAQmxErrChk(functionCall) if( DAQmxFailed(error=(functionCall)) ) goto Error; else

int main(void)
{
    int32       error=0;
    int32       amount; 
    int32       i;
    TaskHandle  taskHandle=0;
    int32       read;
    float64     data[1000];
    char        errBuff[2048]={'\0'};
    char        c = 64;

    /*********************************************/
    // DAQmx Configure Code
    /*********************************************/

    printf("Please enter the amount of voltage checks you wish to run.\n");
    //scanf("%d", &amount);

    while(scanf("%d%c", &amount, &c) !=2)
    {
        getchar();
        puts("Please enter a number.");
    }
    for (i = 0; i < amount; i++)
    {
        DAQmxErrChk (DAQmxCreateTask("",&taskHandle));
        DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev1/ai0","",DAQmx_Val_Cfg_Default,1.0,10.0,DAQmx_Val_Volts,NULL));
        DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandle,"",10000.0,DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,1000));

        /*********************************************/
        // DAQmx Start Code
        /*********************************************/
        DAQmxErrChk (DAQmxStartTask(taskHandle));

        /*********************************************/
        // DAQmx Read Code
        /*********************************************/

        DAQmxErrChk (DAQmxReadAnalogF64(taskHandle,1000,10.0,DAQmx_Val_GroupByChannel,data,1000,&read,NULL));

        printf("Acquired %d points\n",read);


Error:
        if( DAQmxFailed(error) )
            DAQmxGetExtendedErrorInfo(errBuff,2048);
        if( taskHandle!=0 )
        {
            /*********************************************/
            // DAQmx Stop Code
            /*********************************************/
            DAQmxStopTask(taskHandle);
            DAQmxClearTask(taskHandle);
            printf("Updating... ");
        }
    }

    if(i=amount)
    {
        printf("End of Program, press the Enter key to quit\n");
        getchar();      
        if( DAQmxFailed(error) )                
            printf("DAQmx Error: %s\n",errBuff);
    }       
    return 0;
}

此时代码所做的就是打印数字 1000，我也问了它多少次。我很确定这来自这段代码:float64 data[1000];。有人知道如何读取直流电压吗？即使它只是一长串尚未格式化的数字(我可以弄清楚)。

谢谢

Answer 1

显示的数字 1000 来自调用 DAQmxReadAnalogF64() 中的第二个和第七个参数。第二个参数告诉您要为每个 channel 采集多少个样本。 Sevent 参数 (&read) 告诉它在哪里存储每个 channel 实际采集的样本数的结果。所以你要了 1000，得到了 1000。

此时您的程序并未打印出已读入的数据。调用DAQmxReadAnalogF64() 执行数据采集并将其存储在第五个参数中指定的数组中(在您的案例数据)。

在调用之后，您可以使用类似以下内容打印出电压:

for (int i = 0; i < read; i++)
{
    printf("Data point %d has value %f\n",i, data[i]);
}

尽管这显然会打印出所有 1000 个值，但这可能不是您想要的。

如果您要为 NI 库编写代码，那么您应该查看 NI-DAQmx C 引用帮助以获取函数及其参数的说明。他们有很多手册，很容易错过那一本。这些示例通常也很容易适应。