Need to calculate the dimensions of a scale spring.

[aamd2013]

Hi,

I need to calculate the dimensions for a stainless steel spring that is going to be used on a scale. I have only two initial conditions the minimum load of the spring should be 4.196 N, and the length of the spring should be 33 mm. I need to calculate the wire diameter, the spring diameter, and the free lenght . The minimum load of 4.196 N has to give me 0 deflection, then as more weight is added the spring should start deflecting until the maximum load (I don't have restriction with maximum load).
Can someone help me how to start the calculations using this parameters.
Please if I need to give you more information about the conditions let me know.


Thanks

 

[cowski]

(I don't have restriction with maximum load)

If you are designing a scale, surely there is some maximum load you have in mind that the scale/springs will have to accomodate?

 

[aamd2013]

Hi.

Thanks for your question. Yes, I guess I have to determine a Max load restriction. This is the whole system i have to design: It is a scale that will measure the weight of a wire that its weight should be between 15.5grs and 16.178 grs (0.03417lbs-0.03566lbs). The scale will determine if the wire is within specification. The Minimum load that I mentioned that is going to be applied to the spring, is the weight of the tray where the wire is going to be placed to be weighted. So that's why I need cero deflection when the tray is empty, and start deflecting once the wire is on the tray. The system is a rectangular tray with one spring in both extremes of the tray. So i need to design a scale with a high sensitivity, since the wire's weight is too little, the measurements have to be very accurate.

I don't know how to determnine the Max load, since the Minimum load is so much bigger than the load is going to be applied, and I don't want to affect the sensitivity of the spring is the maximum load is too big.

I am giving the conditions again:

Minimum load with cero deflection: 4.196 N
Height of the spring :33mm
Wire mass: 15.5grs and 16.178 grs (0.03417lbs-0.03566lbs)

Thanks

 

[MikeHalloran]

Just buy an analytical balance.
It will come with the enclosure and door necessary to shield the pan from air currents, and probably with an RS232 output that you can use to record the results or interface with your process controls.
It will be much cheaper than trying to make your own.




Mike Halloran
Pembroke Pines, FL, USA

 

[desertfox]

Hi

Firstly you cannot have a load at zero deflection on a spring and further I doubt you will get a spring accurate enough to detect an error go 0.5grms mainly because springs have errors of around 10% on load and position! even the most accurate springs have an error of 3% positive or negative.