- From: Calin A. Culianu <calin_at_ajvar.org>
- Date: Wed, 2 Oct 2002 13:28:14 -0400 (EDT)
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
Received on 2002-10-02Z16:28:14