NI 9215 c series module max sampling rate over 100KS/S/ch

[kevg]

Hi,

I am looking to find the max sample rate of the c-series NI 9215 module if you use an external clk. It says in the data sheet that the max rate is 100ks/s/ch for the this 16 bit synchrounous acquisiton module.

My real question is can you sample at a higher frequency than the 100ks/s/ch for all 4 channels.

I am looking to use multipe NI 9215 modules to sample at 102.8ks/s/ch using an external clk. Has anyone tried this before or know if it is possible to sample at this rate if you use an external clk and trigger line. This was in conjuction with the enet series chasis but now perhaps with the new compact daq  cDAQ-9178?

From searching this forum this post is the only one which discusses thie:This post:http://forums.ni.com/ni/board/message?board.id=5170&message.id=4306&query.id=518758#M4306

From the translator i used seems to suggest the max sample rate can be 110ks/s/ch?? but my translation could be incorrect.

Thanks for any help or advice on how to do this.

Kevg

[MarkGrot]

Yes, you can sample faster than 100kHz with the NI 9215 in a CompactDAQ chassis.

Channel  0:     235,294 Hz

Channels 0-1: 170,940 Hz

Channels 0-2: 134,228 Hz

Channels 0-3: 110,497 Hz

The max rate is determined by the highest channel number in the task.  For example, a task containing only ai0 has a max rate of 235kHz where a task with only ai3 has a max rate of 110kHz.

Yes, you can acquire all four channels at 102.8kHz.  If you use the new cDAQ-9178 chassis, yes, you can use the external PFI line to import your sample clock.  You could also do it on the cDAQ-9172/4 chassis but would need a digital module such as the NI 9401 or NI 9402 to import your sample clock.

[kevg]

Hi Mark,

Thanks for your reply. Thats great. So if i use an external Clk through the PFI lines I can sample at higher than the 100KHz which is stated in the specs.

Can i ask were you found this information as i could seem to see this is the spec's, but i may have missed it?

My issue with the compact daq chassis are they do not have a ethernet connection and we are looking to have multiple daq units in a test field. I have heard that a USB 2 extender could be used but i think these are only limited toapproximately 70Metres. I dont suppose you have have used these and if so what are the bandwidth limitations?

I was looking at using a number of Enet 9125 single chasis modlue as these have the PFI lines and ethernet connection for acquiring numerous singals but a compact daq with several modules would be neater and more cost effective. 

Thanks again.

Message Edited by kevg on 10-06-2009 09:27 AM

[MarkGrot]

I don't believe it's listed in the specification and if you look at the conversion time, cDAQ is going slightly faster than listed.  My guess is that marketing likes nice round numbers.  If you want to double check this you can do it without hardware.  There are two ways off the top of my head:

Download and install NI DAQmx.  Simulate a CompactDAQ chassis and add a NI 9215.  In LabVIEW, you can use the device property node to query the max rate.  Set your active device to your simulated NI 9215, and query AI.MaxSingleChanRate and AI.MaxMultiChaRate.  In C you can use the DAQmxGetDevAIMaxSingleChanRate and DAQmxGetDevAIMaxMultiChanRate  properties.

Download and install NI DAQmx.  Simulate a CompactDAQ chassis and add a NI 9215.  You can run a MAX test panel or use the DAQ Assistant to some quick tasks to try it out.  If you attempt to go too fast, the error will report the max rate.

I don't have any experience with USB extenders but I believe there have been a number of posts on this forum from people who have tried them.  

Message Edited by MarkGrot on 10-06-2009 11:14 AM

[Bauer_CT]

Hi I realize this thread is very old but I just discovered this issue myself. Why would it matter which one channel you're reading, for max sampling rate? Is it secretly just adding all the channels before it? Shouldn't I be able to do the max 250kHz for any single channel? Why is channel AI3 so much slower than channel AI0?

[santo_13]

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@Bauer_CT wrote:
Hi I realize this thread is very old but I just discovered this issue myself. Why would it matter which one channel you're reading, for max sampling rate? Is it secretly just adding all the channels before it? Shouldn't I be able to do the max 250kHz for any single channel? Why is channel AI3 so much slower than channel AI0?

---

Yeah, it looks like something special about this module: it is channel specific and not just count of channels.

This is the snippet from the datasheet

[Kevin_Price]

The nature of the specs sounded pretty strange to me so I tried to test it out via simulated devices in MAX.

Sure enough, ai0 alone on a 9215 seemed to support a 200 kHz sample rate, ai3 alone would not.  The error text listed the max rate for ai3 alone as 110.5 kHz.

Odd, but (seemingly) true.

-Kevin P