PSN-L Email List Message

Subject: Re: EPICS Charge to students
From: "Larry Cochrane" cochrane@..............
Date: Thu, 29 Aug 2002 20:21:33 -0700


I'm not sure what the Colorado School of Mines and Globe program have in
mind as far as producing the system is, but I do have a few comments....

I just don't think it's practical or possible for a business to produce a
sensor / system for only $150.00. Especially a usable and stable long period
device. It would be hard to produce a short period or strong motion sensor
for this price.

To produce a system like this requires some basic parts, no mater what the
actual design looks like. One very important item is a good solid base and
this costs money. Just a slab of aluminum can cost $20 to $30.  This base
will also need to be drilled and taped to hold the sensor parts. This labor
costs money. What I'm getting too here is if you do this with each part I
think anyone will come up with a total cost somewhere near, or more likely,
over $150.00. And that's just for the mechanical parts.

The same thing happens with the electronic. By the time you add up the blank
PC board cost, electronic parts, box, power supply, build and test labor
costs etc etc etc its going to cost somewhere around $100 or more. One way
of getting the cost down is to build a lot of units. After all, one can buy
a very complicated VCR or DVD player for under $100.00. The difference is
they are making a lot (millions?) of units. Selling seismograph systems will
always be a small market. No big company is going to invest the millions of
dollars need to produce a cheap product if they are only doing to sell a few
hindered or even a few thousand, if they are lucky.

I would assume that the Colorado School of Mines or Globe program do not
want to produce the sensor themselves, so a company would need to do it for
them. For a company to make something like this they need to make a profit,
unless your Enron . Lets say that one could keep the parts cost down
to $150.00 and still produce a good system. A company would need to sell the
system for 2 or more times the cost of the raw parts and labor to stay in
business. So now the real cost is $300.00 to $500.00 just like my stuff and
the AS-1.

One other thing. Support. I now spend a few hours each day supporting my
equipment. If some company has a lot of these systems in the field with
teachers who have never setup a system like this the support cost will go
through the roof. This is why a company need to charge may times the raw
parts cost to stay in business.

Larry Cochrane
Redwood City, PSN

----- Original Message -----
From: "John & Jan" 
Sent: Thursday, August 29, 2002 5:49 PM
Subject: Fwd: EPICS Charge to students

This semester at the Colorado School of Mines all 350 freshmen will be
working on the
design of an inexpensive seismic system.  They will be divided into 70
groups of 5 for
this effort.  Because the goal is to design an inexpensive instrument (less
than $150)
some things may have to be sacrificed,  including linearity and single-axis
The $150 limit (exclusive of a PC) would make this instrument a candidate
for the
GLOBE program, an educational program with international scope and
many collaborators that is currently focused on weather, atmosphere, and

I will encourage the students to join mailing lists,  such as this one, to
get information
and advice for their projects.  The PSN group collectively has a wealth of
experience that
they could benefit from.

A letter with added details follows.


>August 20, 2002
>Robert D. Knecht
>Colorado School of Mines
>Dear Dr. Knecht,
>The IRIS Consortium Education and Outreach Committee is pleased that the
>EPICS Project for this
>year will be the design of an inexpensive sensor for seismic
>waves.  Computers, which are widely
>available in K-16 classrooms, have replaced the paper-drum and pen
>recorders of earlier years.
>IRIS has sponsored the development of AmaSeis, a free, PC-based program
>that monitors the real-
>time stream of data from a seismometer so that near and distant
>earthquakes can be easily recorded
>and viewed graphically.
>The principal remaining barrier to more widespread, school-based
>earthquake recording systems is
>the availability of an inexpensive, yet sensitive, long-period seismic
>sensor that can attach to a PC's
>serial port via an analog-to-digital converter.
>The least expensive commercially available system (excluding the PC) costs
>about $500, which
>precludes purchase by very many teachers or schools.  If this cost could
>be reduced to $150 or less,
>it would be within the range of many more budgets and would also be a good
>candidate to become
>an instrument recommended for use by the Globe
>Design Goals and Options
>For the system to be useful in any location on the Earth, it must be able
>to record large earthquakes
>at any distance -- teleseisms in the terminology of seismologists.  This
>requires a good signal to
>noise ratio in the period range from 1 to 20 seconds.
>The following table gives a rough idea of the amplitude and velocity of
>ground motion that would
>be expected from a magnitude 7 earthquake at 90 and 180 degrees distance.
>Magnitude 7 at 90 degrees distance:           amplitude        velocity
>Expected 20s period surface wave amplitude [  5.61E+01 Ám]  [  1.76E+01
>Expected 1s period body wave amplitude     [  7.93E-01 Ám]  [  4.98E+00
>Magnitude 7 at 180 degrees distance:
>Expected 20s period surface wave amplitude [  1.81E+01 Ám]  [  5.68E+00
>(No direct P-phase at this distance.)
>Construction Strategy
>One strategy might be to look at commercially available recording systems,
>such as the AS1
> on display at CSM, the Sprengnether
>, and the designs of
>the Public Seismic
>Network  and
>. Explore ways in which the
>cost of manufacture, and
>hence, the cost of purchase of these instruments could be reduced by
>eliminating expensive or
>carefully machined components.
>Either a high-school teacher with little or no mechanical and fabrication
>skill should be able to
>build one from scratch for about $150, or, if you choose to reduce costs
>by distributing instruments
>in kit form, the cost to the fabricator must be such that an
>easily-assembled kit will sell for less than
>The sensor could be based on the voltage generated by relative motion
>between a coil and magnet,
>on the proximity of a magnet to a Hall-effect sensor, on the amount of
>light reaching a photo diode
>that is partially blocked by a flag, on the strain of a piezoelectric
>crystal, or on the output of a micro
>machined accelerometer similar to those used to trigger the release of an
>automobile's air bag.
>Given that new, high-density, low-cost disk drives are continually coming
>to market, there may
>well be some sophisticated, mass-produced, and yet inexpensive components
>that could also be
>used for this application.
>Recording Options
>The completed system must be able to record data continuously onto a PC
>computer disk, and this
>will require the use of an analog-to-digital converter.
>The Dataq Company sells the DI-154RS for $100 (with educational discount)
>an inexpensive, 12-
>bit, analog to digital converter that could be used for this system.  It
>is model number DI-154.  It
>has terminals for analog input and digital-serial output and is powered by
>the serial port of a PC.
>They also sell a 10-bit unit for $25 (DI-194RS).   
>The free AmaSeis software for seismic recording is available from Alan
>Jones' web site for the DI-
>154RS AD unit.   
>To use the either Dataq AD unit, one would need to construct a sensor that
>would connect to the
>AD via an amplifier and filter circuit.  Because of the cost of the AD,
>either $125 or  $50 would be
>available for the sensor/amplifier/filter combination.
>Another option would be to add an AD with serial output to the
>amplifier/filter circuit to allow  a
>direct connection to the serial port of a PC.  That would cut down on the
>cost, but AmaSeis might
>need to be modified to accept a new serial format.
>Still another option would be to use the PC's game port.  The game port is
>designed to sense the
>resistance of the joy stick.  A field effect transistor (FET) can be used
>to simulate a variable resistor
>and the FET "resistance" can be made to vary with the voltage generated by
>the amplifier/filter
>John C. Lahr
>US Geological Survey
>National Earthquake Information Center
>(303) 273-8596 (tel)
>(303) 273-8600 (fax)
>Thomas Boyd
>Associate Professor
>Department of Geophysics
>Colorado School of Mines
>  (303) 273-3522 (tel)
>(303) 273-3478 (fax)


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