Error -200284 occurred at DAQ Assistant

[hgca2mi]

I tried to acquire the Analog Input from the analog output, 15 ms light pulse at 20 Hz for 10 s every min during 1 hour,  and get this error.  Your help is greatly appreciated.

Error -200284 occurred at DAQ Assistant



Possible Reason(s):

Some or all of the samples requested have not yet been acquired.

To wait for the samples to become available use a longer read timeout or read later in your program. To make the samples available sooner, increase the sample rate. If your task uses a start trigger, make sure that your start trigger is configured correctly. It is also possible that you configured the task for external timing, and no clock was supplied. If this is the case, supply an external clock.

Property: RelativeTo
Requested Value: Current Read Position

Property: Offset
Requested Value: 0

[R Sandoval]

Hello There,

The issue may derive from how the DAQmx Analog Tasks are initiated.  With that said, can you explain your code regarding task creation in more detail?  Are you using Measurement & Automation Explorer to configure the tasks?

[hgca2mi]

I am using LabView SignalExpress 2.0 with the following steps:

1. Setup a repeat condition to repeat 60 iterations.

2. Create Square wave signal of 20 HZ amplitude 2.5V with 2.5V offset of 30% Duty cycle at the sample rate: 1k S/s for 10000 samples.

3. add DAQmx Generate Analog Output ( votage Output Setup range 0-5V)

4. add DAQmx Acquire Analog Input (There is a wire connect the output to the input terminal on an SCB-68 box)

5. add a post-excution delay for 50000 ms.

6. check the Iteration

I got the error when I ran the steps.

Many thanks.

hgca2mi

[R Sandoval]

Hello There,

The error appears to derive from a timeout error from your analog input function.

The computer retrieves the analog input values from the DAQ in chunks.  For example, pretend you specify the transfer size (DAQ to host computer) to 200 points every time you communicate to the DAQ card (when DAQ Assistant is called).  Also, you call this function every 1 second with a timeout of 3 seconds.  If the DAQ buffer only contains 50 points during your first request, then no points will be sent and the time will continue (1 second elapsed).  The subsequent requests produce similar results.  Request 2 does not return anything, and 2 seconds is registered.  Likewise, request 3 also does not return anything, and 3 seconds is registered.  At this point the timeout is reached and an error is prompted stating that the buffer has insufficient points to retrieve.

To overcome this issue, you should either increase your timeout value, reduce the communication chunk size (note: setting this to a very small value will increase communication overhead), or increase your acquisition rate.  I hope this helps.

[hgca2mi]

Hi Roman,

Thank you for the detail explanation. That helps a lot.

I am trying to  achieve the following requirement,  " Create a series of square wave pulses of 15ms  between either 0V (low) or 5V (high)   at 20 Hz for 10 second in every minute for 1 hour "

I  generated  the 0V - 5 V square wave at the frequency of 20Hz with duty cycle of 30% with the block size of 10k samples at the sample rate of 1k S/s,  10 second total,

and then add a post-execution delay for 50k ms then loop it for 60 times. 

When I try to record the output by connect the output into the input port, I can get the 10 sec square wave when I aquired the analog Input. How do I record the 50 ms delay? Is it possible?  Will it be better to generate the 0 volt output for those 50 second?

Thank,

hgc

[GarPar]

Hi hgc-

     If you are recording waveform data to a file, then you will see that there is actually a timestamp (or a delta T) value associated with every value.  If you are looping your entire chunk of code, then you will notice that if you look at the last value from your first iteration to the first value of your next iteration, there is that 50ms delay in time.  If you want to actually record those values along with your waveform, you can just output 0V for 50 ms in software, and then this time will be explicitly recorded.

     I hope this helps.  Have a great day!

Regards,

Gary Parente

Applications Engineer

National Instruments

[Hesron]

hi National Intsrument!

i think it will be a nice thing if you guys explain things with the aid of videos.

thank you