PSN-L Email List Message

Subject: Re: Hekla volcano geophone planned
From: ian ian@...........
Date: Sat, 05 Jan 2008 09:35:41 +0000


actually, I don't think I'm near any limits.  The A/D I use can handle 
20K samples/sec.  I only have 2 instruments (though I sample each on 3 
A/D channels to get the resolution up to 22 bits), so that's only 6 x 
50, or 300 samples/sec.  So I could connect up all of the A/D's 16 input 
channels and still not stress it.

The data server does burn up 80% of the PC's CPU but it's only an old 
800 MHz machine and wouldn't cost much to replace with one twice the 
speed.  Data across the network connection is only 32 characters x 50 or 
1600 bytes/sec.  Less than a 500th of the 100 Mb/s network bandwidth 
(being generous).

All of the above though, implies that you are happy to write your own 
code.  Buying building blocks off the shelf can be very attractive.  For 
multiple instruments you could buy several PSN A/D boards.  To overcome 
the potential problem of connecting up multiple RS232 cables, you could 
use a network terminal server (such as ).  
These aggregate up to 4/8/16/24 rs232 connections on to one network 
connection.  They usually come with software for the pc which creates 
multiple virtual COM ports, so your A/D boards would look like they are 
plugged into an array of COM ports on the PC.

Isn't technology wonderful!



ChrisAtUpw@....... wrote:
> In a message dated 04/01/2008, gpayton880@....... writes:
>     But rather than have 1 sensor on a single socket it is more
>     sensible to
>     have many sensors on a single socket using a data protocol.  This
>     is how
>     I have designed my system.  It sends out a continuous stream (50
>     samples
>     per second) of "(Lehman reading) (geophone reading) (time
>     stamp)".  My
>     graphing program makes a connection to the "data server" and plots
>     the
>     values from the 2 sensors as they arrive.  See
> .
> Hi Ian,
>     The limitation tends to be the total data throughput 
> speed reqired. 50 SPS is quite fast. The ADC sample rate can also 
> impose limitations. This starts to become serious when you have, say 
> several three off three channel sensors on the same ADC.
>     Regards,
>     Chris Chapman



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