hardware timed

[amir_zargar@hotmail.com]

Hi,

i have a very simple VI, and want to synchronize my DAQ with hardware. the labview version is 7.1 and DAQmx is 7.4, my embedded controller is PXI-8176 and my DAQ cars is PXI-4472.

i have this as en error:

Error -200077 occurred at Property Node DAQmx Timing (arg 3) in DAQmx Timing (Sample Clock).vi->TEST-3.vi

Possible reason(s):

Requested value is not a supported value for this property.

Property: SampQuant.SampMode
You Have Requested: Hardware Timed Single Point
You Can Select: Finite Samples, Continuous Samples

Task Name: _unnamedTask<6>

my program is attached, please help me to fix this error.

thanks

Amir

[Ed W]

Hi Amir,

Thank you for posting to the NI forums.  There is a Knowledge Base entry on this exact error message in relation to DSA devices. 

Getting Error -200077 When Doing 1-sample Acquisition With DSA Boards (4472, 4461 etc.)

Like the error message states, you can use either finite or continuous mode in your DAQmx timing VI when using a DSA device.

I hope this helps.  Post back if you have further questions. 

Ed W.

Applications Engineer

National Instruments

[amir_zargar@hotmail.com]

Thanks Ed W.

then do you know, is there any other device than can replace to do this job (hardware timed single point)?

Amir

[Stuart_G]

Amir....before you go and buy or use another board, my question is why do you need to use Hardware Timed Single Pt (HWTSP).  Your original post was that you "wanted to synchronize my DAQ with hardware".  To me that is a little vague about what you really are trying to do, but with that said why do you feel you need HWTSP to do so.  To ask another way what is requiring you to use HWTSP?  Why won't a buffered acquistion work for you?

StuartG

[amir_zargar@hotmail.com]

Hi Stuart,

last week, i was working with an old version of DAQmx and maybe because of that, the buffer size  had a upper limit (32000) and the frequency had a lower limit (1000 Hz), then with this condition and having 3 channels in 1000 Hz and a timed loop of 1ms, i had and i have  an overflow, this error :

Error -200279 occurred at DAQmx Read (Analog 1D DBL NChan 1Samp).vi

Possible reason(s):

Attempted to read samples that are no longer available. The requested sample was previously available, but has since been overwritten.

Increasing the buffer size, reading the data more frequently, or specifying a fixed number of samples to read instead of reading all available samples might correct the problem.

Property: RelativeTo
Corresponding Value: Current Read Position

Property: Offset
Corresponding Value:

Task Name: _unnamedTask<6>

however i think it is supposed that time loop removes one sample form  the buffer at every 1 ms (the same frequency as acquisition) and doesn't let data being overwritten, but in reality it seems different.

with DAQmx 7.4 finally i have tried 250 Hz with a buffer size of 100000 and it is working by now. i attached my program and i appreciate you if you let me know any necessary modification.

thanks

[Stuart_G]

Some Random thoughts.

#1.  You really only want to read 1 sample at a time?  If so then DSA board is probably overkill for you.  But since you already have the board I guess it could work

#2.  The timed loop is not perfectly deterministic on Windows.  Any interrupts, thread switches, etc could and will add jitter to the timed loop.  If you truly need absolute determinism then I suggest RT, however, then I would also suggest using HWTSP which the dSA board doesn't support.  In the way you currently have this setup it will work, but I can see it being late often.  Also, keep in mind any real calculations, etc you add to the inside loop is going to cause jitter.

#3.  You could take a look at the DAQmx examples where the sample clock drives the timed loop.  That might work better in your case.  Use the example finder and search for "timed-loop".  There are a half a dozen examples which show how to use the timed loop using DAQ as a timing source.

I am still unsure about what you are actually trying to do.  These are the best suggestions I can give theorizing on what your app is.

StuartG

[amir_zargar@hotmail.com]

Hi,

First, I thank for good tips in forums, and then I realized a new problem,

I did my acquisition with DAQ-mx 7.4 with a 250 Hz and a buffer of 100 000 samples per channel, and it was working, now, I’ve upgraded Labview to 8 and it doesn’t let me to have a frequency lower than 1000 Hz. Why does acquisition frequency depend to the DAQ-mx version and  What can I do?

Thanks

Amir

[Stuart_G]

That sounds wrong to me.  There is no frequency limit on the acquisition to my knowledge in any version of DAQmx what error do you get when you set it to 250hz?  I am pretty sure you can set the frequency to 250, maybe you are getting some sort of buffer overflow error? 

StuartG

[amir_zargar@hotmail.com]

Hi

Here you are, the error which i got:

Error -200077 occurred at DAQmx Read (Analog 1D DBL NChan 1Samp).vi:2

Possible reason(s):

Requested value is not a supported value for this property.

Property: SampClk.Rate
Requested Value:  250.000000
Minimum Supported Value:  1.0 e3

Task Name: _unnamedTask<7>

and i will stop on DAQmx Read (Analog 1D DBL NChan 1Samp). the frequency is given in DAQmx Timing(sample clock) in continuous samples mode.\

thanks

Amir

[Ed W]

Hi Amir,

The error message that you’re receiving is expected behavior for your device.  NI’s DSA devices have a minimum sampling rate as well as a maximum.  The PXI-4472’s minimum sampling rate is 1kS/s, as the error message indicates.  There is actually a Knowledge Base article that address this issue. 

Errors when Sampling Below Minimum Rates for Dynamic Signal Analyzers

I hope this helps. 

Ed W.

Applications Engineer

National Instruments