Synchronizing Analog and Digital Acquisitions for same event.

[nnarra]

I was measuring analog and digital pulses for same event.Initially both the acquisitions happening at same time and running at same rate,but after some time,digital acquisition going slow and values I was getting are deviated from analog in milliseconds are using MSeries PXI 6254 Card,How can i make both the acquisitions to happen at same rate throughout the test

[dansch]

Hi Captronic Systems,

Thanks for the post! I understand that you are trying to acquire analog and digital inputs together, but are having trouble synchronizing them. I am not sure which ADE you are programming your application in, but there is a very good LabVIEW example which does exactly what you require. This example may be found in the LabVIEW Example Finder (under Help » Find Examples...) by navigating to Hardware Input and Output » DAQmx » Synchronization » Multi-Function » "Multi-Function-Synch AI-Read Dig Chan.vi". In this example, the sample clock source for the digital input task is set to be the ai/SampleClock of the same device (meaning that you are using the same sample clock for both tasks). Additionally, the digital task is started before starting the analog task, so as to ensure that both tasks will start together when the analog input begins. Using this method of sharing a sample clock, you can guarantee that both acquisitions will start at the same time and will always occur at the exact same rate. Hope this helps,

[fesfdwe]

Hi Mr.Daniel S,

Thanks for your reply to my doubt.This example really useful for me and i have one query regarding this.Actually,for executing the example given by you,minimum two DMA channels it require and in our case we are using M Series PXI 6254 DAQ device for acquiring both analog and digital samples.Also we are acquiring analog and digital with different sampling rates.My question is whether this DAQ device supports DMA Transfer,if so,what are all the channels for DMA Transfer,i will be awaiting your reply,

regards,

Naresh N 

[Dan_K]

Hello fesfdwe,

From the DAQ M Series User Manual, page 10-5:

" On PCI, PCI Express, PXI, and PXI Express M Series devices, each measurement and acquisition circuit (that is, AI, AO, and so on) has a dedicated DMA channel. So in most applications, all data transfers use DMA."

It goes on to say that although DMA is the default it is possible to specify the use of interrupts instead.

Regards,

Dan_K

Applications Engineer

National Instruments