Re: Analog Input Board Recommendations

On Wed, Oct 02, 2002 at 02:12:00PM -0400, Calin A. Culianu wrote:
> 
> 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?

The actual time is probably somewhere between.

Even though the A/D converter is "busy" for 5 us converting analog
to digital, it is only sensitive to the analog signal for a short
period.  The A/D converter on that board (Analog Devices AD976A),
for example, is done with the analog signal about 40 ns after the
convert pulse.  So assuming that the board is designed to switch
the mux to the next channel immediately after this time, you can
acquire at a 6.040 us rate and be within the 1 LSB mux settling time.
I would expect this from a well-designed board.



dave...

Received on 2002-10-02Z19:20:57