Re: Analog Input Board Recommendations

Hi Tim,

I was looking at the Measurement Computing specs for the PCI-DAS 6402
board.  They say their board has an input settling time (to 1 LSB) of 6
us, and an A/D conversion time of 5us.  Now let's say I'm switching
channels, do I have to add those two numbers up, or do I take the worst
case of 1 of those numbers to arrive at my settling time?  What I need to
figure out is if it takes 11us or 6us to switch channels on that board?

-Calin

On Wed, 2 Oct 2002, Calin A. Culianu wrote:

> On Wed, 2 Oct 2002, Tim Holy wrote:
>
> > Hi Calin,
> >
> > > By the way where do you get
> > > specs on MUX settling times from NI?  I got their 'spec sheet' for some of
> > > their boards, and it just seems like a glorified advertisement more than a
> > > spec sheet....
> >
> > I've seen it elsewhere for this card specifically (can't remember where), but
> > http://www.ni.com/pdf/products/us/2mhw236-238e1.pdf has the info you seek
> > (see page 16).
>
> Hahhaa.. I actually have this document, but before this spec sheet there
> is a whole bunch of stuff about cabling and thusly I thought the rest of
> the document was all about cabling.  Ok, cool.  I now see that the 6071E,
> with its 2.0us settling time at 0.098% accuracy definitely allows for
> 10kHz sampling on all 64-channels.  There still is some interference, but
> it is so minimal it is pretty much negligible.
>
> >
> > > What do you mean by well-buffered?  I am a programmer more than a hardware
> > > guy, so to me a buffer is simply a big chunk of memory you use for data.
> > > What do you mean by that word in a hardware/signalling context?
> >
> > To "buffer" in this context means to copy the signal in terms of its value
> > (e.g. voltage), but to change other output characteristics (e.g., the
> > current-sourcing capability, so you can charge up that sampling capacitor on
> > the A/D very quickly). The inputs to the board should come from some
> > low-impedence output device, e.g. an amplifier. You can't just connect the
> > wire used to measure the EKG straight to the A/D board, or horrible things
> > will happen to the signal. Perhaps the signals are being routed through an
> > amplifier of some type already. If not...if your signals are around 1mV (just
> > a guess), then you might want to amplify them 1000x with a couple of op
> > amps/channel (and set your filter properties while you're at it). If for some
> > reason you're getting volt-scale signals already, then you will still want a
> > 1x gain op-amp to buffer the signal.
> >
> > Best,
> > --Tim
> >
>
> -Calin
>
>
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Received on 2002-10-02Z17:12:00