PSN-L Email List Message

Subject: Re: Zero-length spring
From: "tchannel" tchannel@..............
Date: Wed, 29 Nov 2006 22:53:52 -0700

Hi John,  Thank you, this is a great posting.   Ted

----- 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: 
> 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 
>>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 
>>>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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