PSN-L Email List Message
Subject: Re: Zero-length spring
From: "tchannel" tchannel@..............
Date: Wed, 29 Nov 2006 23:29:06 -0700
Hi John, I am not too good at math, could you please plug-in some
examples/numbers for this formula so I can understand it better? I think its
k that I am unclear of. I understand the rest. Thanks, Ted
MgA = kSY/(SA)
M = kY/(Ag)
----- Original Message -----
From: "John or Jan Lahr"
Sent: Wednesday, November 29, 2006 10:25 PM
Subject: Zero-length spring
>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
>>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
>>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?
>>From: psn-l-request@.............. [mailto:psn-l-request@.................
>>Behalf Of ChrisAtUpw@.......
>>Sent: Wednesday, November 29, 2006 5:29 PM
>>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?
>> 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
>>>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.
>> Chris Chapman
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