USB interface replacement for NI 6062e ADC

[smiffy]

We have a NI 6062e ADC that plugs into a PCMCIA slot. The nature of our testing environment has damaged either the sockets on the card and/or the pins inside the laptop. I am looking for a suitable replacement that has a USB interface. Can anyone make any recommendations? I would prefer something with a robust connector, rather than screw terminals.

[John_P1]

Hi smiffy,

Depending on your exact requirements, I'd look into one of the following: 

USB 6212 BNC, USB 6221 BNC, USB 6251 BNC

The above USB DAQ devices are nice because they don't require any cable/terminal block.  These boards also have screw terminal versions which sell for a bit cheaper, but if you were looking for the more robust connection these would be a good option.

If you have specific functionality you need to implement we can help narrow down the requirements to select an optimal board.  For instance, if you only require analog input and accuracy isn't as much of a concern, you might look at something like the USB-9201 (but then again, this also uses screw terminals).

Best Regards,

John 

[smiffy]

Thanks John,

We haven't had a need for any analogue or digital outputs, no guarantee that we won't in the future but I doubt that we will. We will need 16 analogue inputs at a data rate of up to 500Hz per channel (no rocket science here). We have a signal conditioner/amplifier (from another manufacturer) that we wish to interface with, and I am now thinking that we might be better off with a unit that has a screw terminal block that we could house in another enclosure to protect the connections.

It has also been suggested that we may need anti-alias filtering for use with accelerometers, can you enlighten me on this topic please?

Cheers,

Smiffy

[John_P1]

Hi Smiffy,

500 Hz per channel * 16 channels is only going to add up to an aggregate rate of 8 kHz--I would look into the USB - 6221 which would more than cover it.

As far as aliasing goes, the concern is that any frequencies above Nyquist (1/2 your sample rate) will be coerced down into the lower frequency band when sampled.  The screenshot below taken from here should give you an idea of what aliasing is and why it occurs:

Fig 1:  The yellow sine wave is the input signal, the blue is the resulting input after it is under-sampled.

Any high frequency components present on your input signal that are aliased into the band of interest will be difficult (if not impossible) to remove with a SW filter.  If your signal does have a high frequency noise component we have two primary solutions available to remove it from our measurements:

1.  Sample at a higher rate:  If using the 6221, we could sample 16 input lines at 15.625k.  This would prevent aliasing up to frequencies of 7.8125k.  The 6251 can sample 4x faster so would not be susceptible to aliasing until frequencies of 31.25k (if acquiring on all 16 lines).

2.  Implement an anti-aliasing filter:  If you have frequency components higher than these frequencies, the 6281 might be worth considering.  Its sample rate falls in between the 6221 and 6251, but it also includes a 40 kHz programmable (on/off) lowpass filter for anti-aliasing purposes.

I hope this helps, be sure to let me know if you have any questions.  I'm still under the assumption that you want a USB form factor.

Best Regards,

John

Message Edited by John P on 11-09-2009 01:13 PM