Why does traditional NiDAQ SCAN_Start() require the count parameter?

[Tree]

I would like to continously monitor 11 analog inputs for 80 seconds with a 2KHz sampling frequency using a 6025E DAQ and NiDAQ 7.1

I am using the SCAN_Start(...) function.

I set my SampleRate to 2000.

I want a Scan Interval of 0. What do I set my ScanRate to? I tried to set my ScanRate to 1000, but received error -10092.

- Tree

[Tree]

My post has an incorrect question.
My question is how do I set my ScanRate?

- Tree

[Jyoti F]

Hello Tree,

The terminology for sampling can be confusing, so first let me define a scan, sample rate, and scan rate. A scan is a set of samples, one from each channel on the list. The sample rate is the rate at which each channel in the scan is sampled and the scan rate is the rate at which one particular channel is sampled, or how often all the channels are sampled. So, if you are only scanning one channel, the sample rate will equal the scan rate.

With that in mind, for multiple channels, the sample rate must be faster than the scan rate. You have done this, however you are not taking into consideration all 11 channels. The sample rate must be large enough so that all the channels can be sampled within one scan period. So, you can either incr
ease the sampling rate or decrease the scan rate. For more information on error -10092 and sampling terminology, look at the KBs linked below.

http://digital.ni.com/public.nsf/websearch/4F80AACDFB3B0B8586256E2300750D9A?OpenDocument
http://digital.ni.com/public.nsf/websearch/DBE7AC32661BCF9B86256AC000682154?OpenDocument

I hope this helps.
Regards,
Jyoti F
National Instruments
Applications Engineer

[Tree]

Hello,

So for example, if I had 2 channels, a proper configuration would be a sample rate of 2Hz and a scan rate of 1Hz?

- Tree