PSN-L Email List Message

Subject: Re: Burr-Brown ADS7807 A/D chips - help!
From: Greg Campbell geonerd@...........
Date: Sun, 28 Jan 2001 01:48:34 -0800

Greetings, Larry and PSN groupies.

I've got a few slightly used surface mount package chips I've rescued
from the engineering trash bin at work.  Can you use them?
I've been meaning to get one of your boards.  What's your price for a
unit w/o an A/D?  Do you offer them in kit form?  (I'd like to build my
own if it will save a few $$$) 

I've also procured about a dozen 3 axis accelerometers that were to be
used in the oil well survey tools I maintain.  These units have various
problems at high temp (125C and up) and are unusable for our probes. 
However, they work fine at room temp.  Sensitivity threshold is <0.1 mG
from DC to ~300 Hz.  I don't know exactly what the rolloff curve looks
like, but by 1KHz the party's just about over.  They need a _clean_ +/-
12V supply and will produce +/- 0.6v at 1 G.  When powered with a good
supply, the noise floor is well below 0.1 mG. 

These accels use a pickoff sensing active feedback loop to 'fly' a
pendulum mass at a nearly static position.  Since the pendulum/pickoff
assembly pivots on (jewel) bearings, there is always a small amount of
friction at in the system.  This 'sticktion' blocks near-zero response a
bit, limiting initial response to acceleration below about 0.3mG,
depending on the individual unit.  The problem is most pronounced
immediately after the tool has been powered up.  Once things start
shaking, the pivot and bearings settle down and the problem largely goes
away.  Rotating the accel so that each channel is at a non-zero
orientation will also help. 

After talking with the company VP, I have a tentative "go-ahead" to let
these guys loose as strong motion sensors.  If any PSN members are
interested, let me know.  For a few $ S/H, I'll send you one.  I do ask
that you be discreet regarding these units.  While the VP may give me a
wink and nod, the company owner (Scrooge come to life) would likely
frown on my "giving away company hardware."  I'll have a final talk with
the VP.  I suspect we may require you guys to ink a non-disclosure type


Larry Cochrane wrote:
> Greetings,
> If anyone on this list has any Burr-Brown ADS7807 A/D converter chips please
> let me know. As most of you know I sell an A/D card that a lot of the PSN
> stations use to record data. I placed an order for more chips back in
> November. I'm now hearing from my distributor that Burr-Brown won't be
> shipping more until April or maybe later. When I placed my order the lead
> time as this month. Needless to say I'm really upset (there are better word,
> but I won't use them)  with Burr-Brown. At this point their right up there
> on my hate list with PG&E and our politicians who got us in the power
> problem...
> As of today I'm out of 16-bit chips. I do have 10 12-bit chips in-stock so I
> can ship boards with them in it and have the user upgrade later when / if I
> get more. Let me know if you can help out.
> Thanks,
> Larry Cochrane
> Redwood City, PSN

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Larry Cochrane <cochrane@..............>