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8 comments
Participant

Join Date: Jul 2013
Posts: 2

Building a Load Cell + Software System to Analyse Dynamic Forces

07/18/2013 4:49 AM

Hi, As the title reads is about as much as I know, I'm groping in the dark and would like pointing in a direction, hopefully the right one. I need to measure forces up to 30kn and would like a unit with a high frequency rate. The nature of the testing means that radio or blue tooth accessibility would be a boon, infra-red too although I've been advised that it's not great in sunlight. To be able to measure peak loads is my primary concern but I would love to have software to analyse the testing further. Where do I begin? Do units like this exist? Is it feasible to build one? Thank you.

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Guru
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#1

Re: Building a Load Cell + Software system to analyse dynamic forces

07/18/2013 7:59 AM

I am not clear on your needs, but places like Omega should be able to provide both technical advice and the components you require.

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Guru
Engineering Fields - Mechanical Engineering -

Join Date: Sep 2009
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#2
In reply to #1

Re: Building a Load Cell + Software system to analyse dynamic forces

07/18/2013 8:14 AM

If Omega doesn't have one, they might be able to make something that will do. Perhaps a combination of heavy and light load cells so you can measure the complete spectrum of forces.

I have used Omega load cells and some of the small hand held data-loggers are very easy to use but I don't know if they had transmitters on them.

I used a bigger data-logger that could record 16 differential voltage readings that could run on battery (for a LONG time) and could be equpped with a wireless transmitter (but probably cut battery time a little).

Drew K

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Commentator

Join Date: Mar 2011
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#3

Re: Building a Load Cell + Software System to Analyse Dynamic Forces

07/18/2013 9:08 AM

If the measurement is tension as opposed to compression, Dillon EDXtremes have a remote option. They have been reliable. If your measurement is compression, they may have a solution for that too.

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#4

Re: Building a Load Cell + Software System to Analyse Dynamic Forces

07/18/2013 9:51 AM

Some questions:

What are you trying to measure the loads on?

Are you controlling the loads?

What range of frequency response are you looking for?

Are the loads strictly axial loads or will it involve torsional loading as well?

How many loads are being measured simultaneously?

Is this an inside or outside application?

Will it be a short-term application (development testing or troubleshooting) or long-term permanent installation?

And many other questions aimed at gleening out the system requirements.

No disrespect intended, but given your low level of qualifications, would you be better served by farming out the job to an outside contractor to: Evaluate the system requirements, provide a cost estimate, design an integrated system, supervise construction, install and commission? (Your company will gain a quality product and you will gain some quality experience by observing this work.)

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#5

Re: Building a Load Cell + Software System to Analyse Dynamic Forces

07/18/2013 12:57 PM

The problem is much more complicated than you think. Since the force transducer will be part of the structure due to the fact that forces (and torques) are measured "in series" its presence will modify the dynamic response of considered structure!

The sensor has to be defined considering this aspect especially if you aim at high dynamic peaks. The choice can be optimized ONLY if the structure is known.

I know what I write since I designed and design special sensors. What you should also consider if at same time at same "point" you have to determine only one vector or several. Sensors can be done for up to 6 degrees of liberty (3 forces and 3 torques).

If you need a support before you discuss with a supplier in order to be sure if you get the right counsel you may use the privet channel on CR4 if your problem has to be considered as confidential.

The first step is to define what you need and if a standard product can fulfill the requirements or not. As for the conditioner and transmission of data there are so many solutions that you will never have a real problem.

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Participant

Join Date: Jul 2013
Posts: 2
#6
In reply to #5

Re: Building a Load Cell + Software System to Analyse Dynamic Forces

07/18/2013 9:07 PM

Thanks for all the replies. I'm just leaving for the weekend but wanted to state more clearly who I am and what I intend to do. I've worked as a rigger/treeworker for the last decade and have always been curious about the load increase/decrease of roped sections of wood. tree rigging scenarios usually consist of a pulley toward the top of the tree, a rope runs through this and is tied at one end to the branch or block of wood that is to be cut and the other end is wrapped around a circular steel or aluminium bollard at the bottom of the tree to add friction. A simple friction/no-friction system but with a huge amount of load force variable. I want to study this. It is my own project with limited funding. Thanks again for the replies, I'll read them carefully on my return next week. regards

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#8
In reply to #6

Re: Building a Load Cell + Software System to Analyse Dynamic Forces

07/19/2013 9:26 AM

You might not want to put an in-line tension load cell like this because you would need to buy a separate logger like this, plus you would need to place it in line with the load and that may not be acceptable.

You could use an accelerometer and then derive the maximum force exerted on the ropes. This accelerometer (that I used for a research project a few years ago) will measure and record acceleration in one device. It is fairly rugged and could be affixed to the log/branch with wood screws fairly quickly then removed and attached to the next one. You could download the entire day's data at the end and view it in a nice graph.

You might be able to derive the load by using a video recording. You would have to kow the weight of the wood and be able to measure the distance it falls then the distance it decelerates and the time. You can watch some videos on youtube on dynamics (khan academy) to see if this might be an option.

Drew K

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#7

Re: Building a Load Cell + Software System to Analyse Dynamic Forces

07/19/2013 12:37 AM

I want to think, just feed the output of a load cell to an oscilloscope. This would probably take some experimenting to find the right ranges. I don't know how serious any secondary effects would be from the changing millivoltage (e.g., induction).

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