PSN-L Message - Subject: Re: Instrument quality

In a message dated 19/10/2009, rpratt@............. writes:

There are also many battles out he= re that=20 need fighting in addition to getting the last nanometre resolu= tion=20 from a home-brew seismometer.

Hi Randy,

Thanks for the feedback and for your differen= t=20 perspective.

Sure, but my Email was not primarily concerne= d with=20 trying to get the last nanometre of sensitivity, but with whether the thin= g=20 works at all !

Will the detection of only one earthquake a= MONTH,=20 when it could and should be several every WEEK, either spark or= =20 maintain any significant interest in any of your kids? This seems more tha= n a=20 bit unlikely to me.

And encouraging someone to make a considerabl= e=20 effort to build equipment which then doesn't work will definitely kill=20 off ANY interest !

Quote: "Do your homework! A lot of folks out there have already done= this,=20 save yourself time, effort, and money by doing some research."

So what 'fruits' of caveman's 'research'= seem=20 have actually made it through to the design?

A very noisy, non linear photo detector was= =20 chosen

A highly temperature dependant photo emitter= was=20 chosen The excitation current was neither stabilised nor temperature=20 compensated

A single ended electronic construction was ch= osen,=20 which does not reduce any common mode effects

A multi filament suspension was chosen

No details of how to design the sensor to mat= ch the=20 frequency range of seismic signals seems to be given

No details of how to design and adjust= the=20 damper to give 0.7 critical damping seems to be given

Getting adequate seismic detection=20 sensitivity is not normally a problem with optical, electromagne= tic,=20 magnetic or capacitor sensors, in my experience. I welcome equipment and= =20 suggestions which work.

Note that caveman had detailed drawings of a= Wood=20 Anderson seismometer available to copy / inspire him. Richter used several= WA=20 seismometers to develop his Earthquake Magnitude Scale in 1935, so we can= assume=20 that they worked reasonably well.

For the past nine years I have= been=20 involved with a regional science fair and have not seen a single seismom= eter=20 project.

So, having identified one of the problems,=20 can YOU help correct it, please? Is this simply because the stud= ents=20 download a list of project suggestions and seismometers are just not= on it?=20 Provide information sources and design help? Maybe publicise som= e=20 seismic projects which actually DO work? Put them on psn?

I had one highschool tea= cher who let=20 me operate my Lehman from her classroom for a couple weeks each year = but=20 now she is gone and there is zero interest in seismology in the area. From= where=20 I sit there will not be any new seismologists to use those last bits of=20 resolution.

How have you been trying to get kids interest= ed in=20 Seismology?

Anyone providing a spark of ima= gination and=20 an avenue of entry for interested young minds is making a great contribu= tion=20 to seismology or more broadly science. Earth science is falling ou= t of=20 classroom time in favour or green and alternative energy. =20

NOT around OUR neck of the woods!! A goo= d=20 quality working Lehman was designed for schools and marketed from Easter= 2007.=20 Sales since then have exceeded 400 systems. This is a successful project= and=20 we expand further into Europe next year. See http://www.bgs.ac.uk/schoo= lseismology/ and=20 click on 'Seismometers'.

Remember that we have just 1/5 the population= of=20 the USA.

I would be quite happy to pass on some detail= s of=20 the design. There is a handbook on the website. There is considerable enth= usiasm=20 amongst our pupils for 'Real Science with Real Seismic Signals'. It is 'th= eir'=20 seismometer and small interested groups run it, analyse the quakes with he= lp=20 from AmaSeis, plot them on a world map and keep records. They also ge= t=20 considerable credit for having done a practical scientific project wh= en=20 they apply for a place at University.

What will give a student more= pride and=20 motivation, connecting a professional device with no understanding= of=20 it or constructing a caveman device and recording a distant quake?&= nbsp;=20 We are up against Facebook and IPhones for kids time and energy.<= /DIV>

Randy

What professional devices are you considering= ?=20

Are you suggesting that it is not possib= le to=20 make a good quality DIY seismometer?

Where is the evidence that the cave= man=20 device can give an even marginally adequate performance?

One quake a month (maybe) will not provide mu= ch=20 competition for Facebook or an IPhone, but it might generate a= =20 few Twitters.

A few years back, I helped one of your studen= ts=20 with his seismic project - very long range help! We discussed the design= =20 requirements, principles and details. He had a friend helping with some=20 machining, but made the design choices himself. He produced a good wo= rking=20 seismometer and a full written account, complete with recordings of= quakes=20 and comparison records from a local broad band seismometer. They were almo= st=20 identical. He entered this in a Science Fair and won a First Prize.=

You need many more like him.

What you do seem to be lacking in the USA is= an=20 inexpensive school seismometer responding flat with velocity from about 5= Hz to=20 20 seconds. The response must be independant of temperature. It must be ea= sy to=20 set up and operate. Iris seem to be insisting on a vertical sensor.= It=20 would be preferable if it was compensated for variations in air pressure,= since=20 these are the predominant source of sensor noise.

What do you suggest?

Regards,

Chris Chapman

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