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Subject: AD698 chip
From: Randall Peters PETERS_RD@..........
Date: Sun, 20 Jan 2008 07:39:39 -0500
Have you actually built an instrument with the AD698 chip and determined that it is unsuitable for
I remember you telling me this some time ago; but it turns out that Denny Goodwin (mentioned in the paper
that John and I just wrote) put together a circuit for me, also some time ago. Only in the last month
did I try his breadboarded unit. He had been unsuccessful with it due to a solder bridge that I found
only after looking at the board carefully with magnification.
You will remember that for much of the two decades I have been using my fully differential
capacitive sensors for internal friction research--that the work-horse for that work was the NE5521 chip
that is no longer manufactured (following the fire at the plant in France). Well, I have done a direct
comparison of the AD698 with the Ne5521 and do not find a great enough performance difference to agree
with your claim! In fact, with the prototype new vertical that I recently built (the details of which I
will soon share with list-serve readers), it picked up the Charlotte Is earthquake with this chip, even
though the instrument was sitting on a lab bench here in the physics building. So I don't think you can
make a defensible claim that the chip is unsuitable for seismometers. Insofar as expense is concerned,
the webpage I recently viewed at Analog Devices indicates a price of about $25 (straight from the
companry) for the version that I would use (in large quantities). I haven't enquired about single chip
prices, although I know from Larry Cochrane that if bought from some of the 'distributors' it is indeed
hideously expensive. They love to mark-up units, evidently in this case by a huge amount.
The price I mention for ADC's in our paper ($25) is not for ADC chips that require peripheral
components and labor to make operational, but rather the ones 'ready to go' from the distributor (like
the 10-bit unit from Dataq).
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