what's the differentce between niScope Read.vi and niScope Fetch.vi?

[emckiller33]

Dear All,

My question is as the topic said:"what's the difference between niScope read and niScope Fetch".

Cheers,

Richard

[balexand]

The Read VI performs a few more operations on the driver compared to the Fetch VI.  The main difference is that the Read VI will initiate an acquisition, but the Fetch VI only works if an acquisition has previously been initiated with the Initiate Acquisition VI.

The Read VI is simpler, but the Initiate Acquisition VI + Fetch VI allows for more advanced features and control.

Read - Initiates an acquisition, waits for it to complete, and acquires data.

http://zone.ni.com/reference/en-XX/help/370592AB-01/scopeviref/niscope_read__poly/

Initiate Acquisition - Initiates a waveform acquisition.

http://zone.ni.com/reference/en-XX/help/370592AB-01/scopeviref/niscope_initiate_acquisition/

Fetch - Retrieves data that the digitizer has acquired from a previously initiated acquisition.

http://zone.ni.com/reference/en-XX/help/370592AB-01/scopeviref/niscope_fetch__poly/

[emckiller33]

Many Thanks for your clarification. Furthermore question, can niScope Read.vi to realise the continuous data acquisition?

[balexand]

For continuous data acquisition, you should initiate acquisition, start the acquisition with a trigger (or use an immediate start trigger), and then call fetch in a loop continuously.

There are examples of this if you go to Help->Find Examples... in LabVIEW, and then select Hardware Input and Output->Modular Instruments->NI-SCOPE (High-Speed Digitizers)->Continuous Acquisition.

[emckiller33]

Hi, Balexand,

when I try to realise continuous acquisition,  I found that very strange thing as the below shown,   the waveformchart shows that the sampled signal are not continunous.     please check my continunous acquisition_niScope.vi.   Does some parameter have  been setup wrong?

[balexand]

I can't see the block diagram of your VI, it is password protected.

[emckiller33]

sorry, please see this attachment.

[balexand]

The issue is that you have the Initiate sub VI inside of the while loop.  To do a continuous acquisition, you should initiate the acquisition once before the loop, and then call Fetch inside of the loop continuously.