A Suitable laptop for using USB-6255

[niranjancs]

Hello,

I am currently setting up a portable multi-function DAQ system using USB 6255 (80 AI, 1.25 MS/s, 24 DIO, 2 AO).

1) Could you kindly suggest me a suitable laptop for the current DAQ, considering heating and latency issues? My experiments generally run for 2 to 3 hours.

2) The description says that its a USB 2.0 port (480Mbps) for communication. Would there be latency issues when multiple channels are used? The manual says that the sampling would be about 750 KSps with multiple channel usage. (http://www.ni.com/pdf/manuals/375215c.pdf)

3) Are there USB DAQ boards where we could systematically set the sampling rate of individual channels?

[Cy_Rybicki]

1. The laptop you want depends on what you are doing with the data being collected. If all you are doing is acquiring and logging using LabVIEW, then meeting the minimum LabVIEW requirements would be sufficient which any mid-range laptop will accomplish (http://www.ni.com/product-documentation/53740/en/). All sampling is done in the DAQ hardware and buffered before being transferred to the PC, so unless you are trying to do real-time control I'm latency shouldn't be an issue.
2. Are you concerned about latency, or bandwidth? If the DAQ board uses a USB 2.0 port then so long as you are using USB 2.0 or higher on your laptop then you should be fine.
3. Are you saying you want different sampling rates for individual channels? If that is the case then you want simultaneous sampling rather than multiplexed, which is what the USB 6255 does. There are plenty of options listed on NI's website depending on exactly what you are looking for (http://www.ni.com/en-us/shop/select/multifunction-io-device).

[Kevin_Price]

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Are you saying you want different sampling rates for individual channels? If that is the case then you want simultaneous sampling rather than multiplexed, which is what the USB 6255 does. 

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I don't think this is correct.  Whether multiplexed or simultaneously sampled, most NI devices only have one timing engine available for AI.   All channels get sampled at the same *rate* either way.

One strategy for multi-rate sampling is to perform hardware sampling at the highest rate needed and then downsample some of the channels in software.  This gives an opportunity to do filtering, averaging, etc.

Another strategy might be to use separate devices to accomplish multi-rate sampling direct in hardware.  If your channel count isn't very high, it might be more cost effective to consider a cDAQ-based system rather than several individual USB MIO devices.  Newer cDAQ chassis (what's a better plural form for chassis?  chassis-es?) have multiple timing engines available -- modules can use their own or share.

-Kevin P

[Cy_Rybicki]

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@Kevin_Price wrote:

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Are you saying you want different sampling rates for individual channels? If that is the case then you want simultaneous sampling rather than multiplexed, which is what the USB 6255 does. 

---

I don't think this is correct.  Whether multiplexed or simultaneously sampled, most NI devices only have one timing engine available for AI.   All channels get sampled at the same *rate* either way.

One strategy for multi-rate sampling is to perform hardware sampling at the highest rate needed and then downsample some of the channels in software.  This gives an opportunity to do filtering, averaging, etc.

Another strategy might be to use separate devices to accomplish multi-rate sampling direct in hardware.  If your channel count isn't very high, it might be more cost effective to consider a cDAQ-based system rather than several individual USB MIO devices.  Newer cDAQ chassis (what's a better plural form for chassis?  chassis-es?) have multiple timing engines available -- modules can use their own or share.

-Kevin P

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You are correct, I had not considered the timing engine aspect.