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Subject: Zero-length spring
From: John or Jan Lahr JohnJan@........
Date: Wed, 29 Nov 2006 21:25:35 -0800

I just wrote up a page describing why a zero-length spring provides a 
vertical sensor with a long period 
response.  See:


At 06:00 PM 11/29/2006, you wrote:
>Hi Chris, Yes the coil is on the arm and the magnet(assembly) is on 
>the baseplate. This is a Lehman similar to the one you built.  Just 
>to repeat myself, it is now 6:30 pm here and the trace has gone from 
>daytime noise, to very still and will remain quiet until appx 8:37 to 8:50am
>Nothing appears on the helicorer, except earthquakes, during the 
>night.  So I don't think the sensor is sticking etc, at night all is 
>working perfectly.
>The noise doesn't start exactly on the minute, each morning, I see 
>no pattern, other than the first noise starts around 8:37 am all day 
>even on Sundays and Holidays.
>There is some sort of pumping? station one mile away, I don't even 
>know what it is but it has a large engine on a concrete slab, and a 
>block building next to the outdoor equipment.  Maybe I should drive 
>over there at 8:33am, and see if the ground shakes.
>(Is the pickup coil on the moving arm and the magnet on the floor / 
>Chris, Now on the zero length spring, do I understand that if I hang 
>the spring, add enough wt to start it to extend, then add 2# and 
>measure, then add another 2# and measure, continue doing 
>this.........say the first 2# expanded 1" the next 2# expanded another 1"
>If I did this 5 times, 2+2+2+2+2= 10#  The expansions would be 
>1"+1"+1"+1"+1"= 5"?
>In other words the same force would be required to move the same 
>distance thought out the length of expansion?
>If so, is this why they use a zero length springs on the vertical 
>sensors so movement is uniform?
>The length is not so important 20" vs 28" but it need so pull 
>evenly, vs easy at first and get harder at the end?
>-----Original Message-----
>From: psn-l-request@.............. 
>[mailto:psn-l-request@................. Behalf Of ChrisAtUpw@.......
>Sent: Wednesday, November 29, 2006 5:29 PM
>To: psn-l@..............
>Subject: Re: School project
>In a message dated 2006/11/29, tchannel@.............. writes:
>>I am still trying to eliminate my daytime noise, or at least 
>>identify it. It was suggested I remove the magnet from the coil 
>>area to see if the noise continued, if so it might be electrical, 
>>like RF, communications etc. using the coil and cables as antenna. 
>>During a noisy hour I remove the magnet, from the coil.  All the 
>>noise disappeared, the helicorer was just a flat line. After a 
>>while, I reinstalled the magnet surrounding the coil and the noise 
>>reappeared. Note: I only get these spikes between 8am and 5pm, the 
>>night time hours are very quiet.
>>Q.  Should I conclude that this means that it can not be 
>>electrical, ie, radio interference, but must be something creating vibrations?
>Hi Ted,
>        This suggests very strongly that it is not RFI or pulse 
> feedback from the power wiring.
>        What is the construction of your seismometer? Is the pickup 
> coil on the moving arm and the magnet on the floor / baseplate?
>>Q. On a different subject. Thanks to your input, I now have a 
>>better understanding of LaCoste zero length spring suspension, and 
>>how it is applied.
>>But I don't understand (what is zero length) or how to find if a 
>>spring is zero length.  Perhaps someone could walk me thru this 
>>using a "screen door spring" as an example.
>        Extension springs are wound with a considerable internal 
> tension - you have to pull them fairly hard to get them to extend at all.
>        You hang the spring vertically and measure the distance 
> between the loop ends. Then you add just enough weight to start to 
> extend the spring, measure the separation, increase the weight etc 
> until you have maybe 5 points of length vs weight. Then you plot 
> the points on a graph and extend the line joining them back to the 
> axis. If the line passes through the zero weight / zero length 
> point, you have a zero length spring. Hopefully, it will give a -ve 
> length for a zero load.
>        Regards,
>        Chris Chapman


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