Hello leoher96,
I see various things in your code that you shared, I will list them here:
First of all you are opening and closing your tasks in every iteration of you while loop, the best practice is to open and configure you tasks before the while loop, stop and clear your tasks after the while loop and inside the while loop do you writes and reads.
//Open tasks
//Configure tasks
while(1) //you could just use a 1 to make the while run indefinitely)
{
//reads and writes
}
//Stop tasks
//clear tasks
Next, in your ReadVoltageLevel() function, you read a finite array of measurements (you create an AI task and configure timing with 1 kHz sample rate and 25 samples per channel, then read 100 samples, and only print in console the first sample in the array, which clearly means you are reading a whole more sample than the ones you are using. If you are only interested in one sample, you could just configure a Software timed mode and acquire the sample when you request it. To do this, simply create the task as you have previously done, skip the configure timing function and use the DAQmxReadAnalogScalarF64() function, as this reads a single sample.
void ReadVoltageLevel()
{
TaskHandle taskHandle = 0;
int32 read;
float64 data;
DAQmxCreateTask("", &taskHandle);
DAQmxCreateAIVoltageChan(taskHandle, "Dev1/ai4", "", DAQmx_Val_NRSE, 0, 5, DAQmx_Val_Volts, NULL);
DAQmxStartTask(taskHandle);
DAQmxReadAnalogScalarF64(taskHandle, 10.0, &data, 0);
DAQmxStopTask(taskHandle);
DAQmxClearTask(taskHandle);
printf("Tank 1 Level is: %f \n ", data);
}
The write voltage function has the same issue, you create an array of 1000 elements, all with 0 value, and write this to the analog output channel. When working with finite analog output, you should write the data BEFORE starting the task, that's why there is probably a mismatch between written values and read value. For your application, I would recommend following the single point analog output, to which you follow a similar code for the single point analog input.
void WritteVoltageLevel()
{
TaskHandle taskHandle = 0;
float64 dataW;
dataW=0; //pump capacity
DAQmxCreateTask("", &taskHandle);
DAQmxCreateAOVoltageChan(taskHandle, "Dev1/ao0", "", -10, 10, DAQmx_Val_Volts , NULL);
DAQmxStartTask(taskHandle);
DAQmxWriteAnalogScalarF64(taskHandle, 1, 10.0, dataW, 0);
DAQmxStopTask(taskHandle);
DAQmxClearTask(taskHandle);
}
If you are using LabWIndows/CVI, you can use some examples to start developing your code, I recommend the following ones (found in the NI Example Finder in LabWindows/CVI):
Hardware Input and Output > DAQmx > Analog Generation > Voltage > VoltUpdate.prj
Hardware Input and Output > DAQmx > Analog Measurements > Slow Varying Voltage Signals > OneSample.prj
I hope this information helps you and your application.
Fernando Becerra | Field Applications Engineer | National Instruments | CLA | CTD
