PSN-L Email List Message

Subject: Re: EPICS Charge to students
From: ian@...........
Date: Fri, 30 Aug 2002 14:32:41 +0100 (BST)

looking at the epics spec has me wondering about cheap sensors.  I like to 
think radical and here's one which may well be so but also nice and cheap.

The thought is of a cube of concrete, say 100 Kg in mass, sitting on springs at 
each corner.  This sits on a concrete floor with a piezo crystal mounted 
underneath the centre of the block.  The piezo is compressed against the block 
to bias the sensor by an adjustable platform.  

Based on the figures quoted by the epics requirement for a 180 degree away mag 
7 seism, the inertia of the block should produce a force of about 10 
microNewtons (feel free to check this figure!).  The hope is that this would 
produce a measurable voltage change by the crystal.

To make this all nice and cheap, you can pour your own concrete block, perhaps 
consider using car engine valve springs (no idea what period this would give) 
and a crystal from the likes of a hand-held gas stove lighter.

This doesn't get you a system for $150 but it may help to reduce costs.

I'd appreciate comments on what sort of signal might be produced from the 
sensor and the resonant freq.

A challenge!  I might build one myself too...


Ian Smith

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