PSN-L Email List Message
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: http://www.jclahr.com/science/psn/zero/index.html
Cheers,
John
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 /
>baseplate?)
>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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