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I can't set sample rate for two channels acquisition with Lab-PC+ using LabWindow/CVI

When I try doing continous acqusition of only one channel using LabWindow/CVI on Lab-PC+ the channel is sampled at given rate, but when I acqusitie two channels at once sample rate "goes crazy", I mean it doesn't obey given limit. Whhat's hapenning? How can I fix it?
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Mucha

Make sure you are using the Lab_ISCAN NI-DAQ functions for your acquisition. Also, make sure you are using correct values for sampInterval and scanInterval when calling Lab_ISCAN_Start.

sampInterval is the interval of the timebase between sampling each channel. To determine the time between the samples of each channel, mulitply the sampTimebase by the sampInterval.

scanInterval is the length of time that elapses between scans. Make sure that the scanInterval is greater than or equal to sampInterval*numChans + 5us.

Also, make sure to call DAQ_Clear before your program terminates or unpredictable behavior might occur.

Brian
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Thank you for the answer, but I'm not sure if I understand what you mean. I use AIStartAcquisition and AIReadAcquisition function from the CVI librabry. I don't know what are Lab-ISCAN functions. Where can I find them? Who to use them? Could you possibly give me some more clearings?
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