problem digital pulse aquasition with NI USB 6008

Signal acquisition, processing and output
mformazhar
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problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

hi



i am trying to creat a digital pluse of user defined high and low pluse time, then i aquired this signal back via analog input channel of DAQ ni USB 6008.

it is giving me problem when i set the PULSE HIGH TIME to 1000ms and PULSE LOW TIME to 1000ms. it some time shows randomly nothing or some time continusly high pulse or low, but not exactly 1 second high or 1 second low all the time.

my first question is that is it the right approach to creat a digital pulse or there is some other efficient way to create such pulse?

second why it is skipping a cycle durring the aquasition, because when i connect the digital output to osciliscope it seems to be OK but when i aquired the same pulse back in the vi it works fine for like 10 cycles and then shows some kind of noise for 2 to 3 cycles repeatedly and then again back to normal transitions?

plz have a look on my vi,i am posting the vi for some good suggestions?

it really makes me worried why it is not working as expected.



thanks
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Eugen Graf

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Re: problem digital pulse aquasition with NI USB 6008

Сообщение Eugen Graf »

Hello!

Would you attach the VI where you read the signal back?
mformazhar
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

i am reading back in the same vi u can see here in attached image , i am taking the digital output back from ANALOG channel input AI0 of DAQ 6008.
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Eugen Graf

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Re: problem digital pulse aquasition with NI USB 6008

Сообщение Eugen Graf »

Ok, you need BUFFERED reading of data. Do you use buffered reading?
If not, than some data will be lost.
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

how could i do do this can u plz explain, i am new to labview, thanks
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение Eugen Graf »

So, first thing - take DAQmx VIs for acquisition, as you made in pulse generating. Don't use DAQ Assistant.
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

when i right click on the DAQ assitant it shows me an option convert to DAQmx code, can i use that option?
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

yes please i did it now what to do next?
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mformazhar
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

i am looking forward to your suggestions eg
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение Eugen Graf »

I didn't look your VIs, but my other suggestion is - may/should be you can't use one device for input and output on the same time.
You can always acquire data, and sometimes reconfigure your interface for output and set your pulse to true or false.

I will look your VIs, bot I have not enough time now :wink:
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Konstantin Sumenko

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Re: problem digital pulse aquasition with NI USB 6008

Сообщение Konstantin Sumenko »

I can't see your code (save it to 8.5). As for attached screen:
1) What is an acquisition rate set by Daq Assistant?
2) You have additional 250ms delay.
eg писал(а):I didn't look your VIs, but my other suggestion is - may/should be you can't use one device for input and output on the same time.
I don't remember this. But at the driver's side (DAQmx) everything is ok: they are multithred. As for device side, perfomance can depend on ADC's discretisation frequency. But when I used NI-USB 6009 to acquire data via ADC at 4000 KHz rate and to control digital potentiometer via digital ports (by cycle pushing)- everything was fine.
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

hi crowbar

here is the attached file compatible to 8.5
i am aquiring 1000 samples
i have checked it without the 250ms delay but still got the same response as u can see in the images above.
plz have a look and guide me what i gonna do now, one suggestion from (eg) was to Buffer read
but i dont know how to implement that?

kindly help me out i really need to figureout why it is happening???

Regards
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение Konstantin Sumenko »

I w'll look at your code soon.
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение mformazhar »

thanks i am looking forward to ur kind suggestions
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Re: problem digital pulse aquasition with NI USB 6008

Сообщение Konstantin Sumenko »

Sorry for delay. So once back: you'd checked with oscilloscope: everything was fine?
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