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Looking for software based strain guage indicator/ conditoner. Anyone know of one?
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USnavy


Nov 21, 2011, 10:12 AM
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Looking for software based strain guage indicator/ conditoner. Anyone know of one?
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I am looking for a software based strain gauge indicator/ conditioner that I can load up on my laptop and take to the crag. I want to study the forces involved in various lead falls, so the software would need a sample rate of at least 1,000 samples per second to capture dynamic peak loading. I have been using a bench top strain gauge indicator connected to a power inverter and 12 volt battery, but its a PIA to take it to the crag, so it seems like a software application would be easier.


(This post was edited by USnavy on Nov 21, 2011, 11:53 AM)


JimTitt


Nov 21, 2011, 10:32 AM
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Re: [USnavy] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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I use a USB conditioner which is exactly what you need, they power the load cell through the USB port so you donīt need an externalysupply and then condition the signal, the software allows you to do almost everything like usual!

The max scan rate is 500hz but for lead falls where the impacts are in reality slow this is plenty enough, believe me. You get a file in csv which you open with exel or open office calc or similar and away you go.

The only company I know who sells them is http://www.loadcellshop.co.uk/All-Products-By-Photo/76-USB-Load-Cell-Adapter.html but there could be a US supplier out there as well.

Jim


USnavy


Nov 21, 2011, 12:35 PM
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Re: [JimTitt] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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JimTitt wrote:
I use a USB conditioner which is exactly what you need, they power the load cell through the USB port so you donīt need an externalysupply and then condition the signal, the software allows you to do almost everything like usual!

The max scan rate is 500hz but for lead falls where the impacts are in reality slow this is plenty enough, believe me. You get a file in csv which you open with exel or open office calc or similar and away you go.

The only company I know who sells them is http://www.loadcellshop.co.uk/All-Products-By-Photo/76-USB-Load-Cell-Adapter.html but there could be a US supplier out there as well.

Jim
That is exactly what I need, thanks. But there seems to be a few issues with it. It only has a 5V output voltage, the industry standard is 10V. That means there is only a 15mV range between 0 lbs. and 10,000lbs. Thats a pretty narrow resolution, it decreases the accuracy of the readings. Also being that its connected to the USB, I hope it simply does not pass the 5VDC output of the USB port to the load cell. Being that most load cells have a voltage reduction of 3mV/V, a change of only 1mV on the output side could cause a 500+ lbs. change in the reading. So the load cell needs to see an incredibly stable power supply. That seems like it would be a hard task to achieve with a USB conditioner considering that the USB output of a computer is not that well regulated and will change depending on battery levels and load. The conditioner would need to be highly regulated and capable of creating a perfectly stable output even with high noise on the USB port and voltage fluctuations which are inherent in the not-so-tightly regulated USB output supply.


(This post was edited by USnavy on Nov 21, 2011, 12:39 PM)


JimTitt


Nov 21, 2011, 2:57 PM
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Re: [USnavy] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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You can either believe they know what they are doing or not.
I find it easy to believe they achieve a stable output for the load cell since my other cells work variously off AA cells, a lead-acid battery and a DC inverter, none of which are particularly known for stable input voltages.

Mine (I have 2) are stable and accurate and continue to hold their calibration and retain the calibration for other load cells.

Edit to add:- If you order from them the shop software doesnīt recognise where you are (unless they have changed it) so you need to contact them and they will give you a code to identify the shipping cost. And I had trouble downloading the software, my anti-virus program corrupted the exe. files but I got it o.k. by downloading direct from http://www.mantracourt.co.uk/
Anbd donīt forget you need some way of calibrating, either test weights or the calibration values for your cell.


(This post was edited by JimTitt on Nov 21, 2011, 11:17 PM)


chalked4dyno


Nov 21, 2011, 5:07 PM
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Re: [USnavy] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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5 or so yearsI built a system for doing field drop-tests about 5 years ago. I developed the acquisition software in a student version of labvi labview as it was an academic project. My loadcell was amplified and I used a 0-5vdc usb input module.

The most interesting part (I think) was my loadcell, which was custom made by strain-guaging a rap ring with 2 dog-bones sewn on (thanks again Jim E!). It was far better suited to the application than anything I could find off the shelf. Because of its light weight it could be used to measure forces at the climber. The report should serve as a "how-to build", if you're interrested, send me a msg and I'll gladly send you the report.


USnavy


Nov 22, 2011, 2:45 AM
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Re: [JimTitt] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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JimTitt wrote:
You can either believe they know what they are doing or not.
I find it easy to believe they achieve a stable output for the load cell since my other cells work variously off AA cells, a lead-acid battery and a DC inverter, none of which are particularly known for stable input voltages.

Mine (I have 2) are stable and accurate and continue to hold their calibration and retain the calibration for other load cells.

Edit to add:- If you order from them the shop software doesnīt recognise where you are (unless they have changed it) so you need to contact them and they will give you a code to identify the shipping cost. And I had trouble downloading the software, my anti-virus program corrupted the exe. files but I got it o.k. by downloading direct from http://www.mantracourt.co.uk/
Anbd donīt forget you need some way of calibrating, either test weights or the calibration values for your cell.
Alright, thanks for the info. I found a US dealer, http://swann-associates.com/load-cell-amplifiers/strain-gauge-to-usb-convertor-dscusb/

I have a question about calibrating. Instead of using weights, can I enter the mV/V value into the software? I have never calibrated one of these before, the one I bought was already calibrated with a load cell, but I figure to obtain the mV/V value of the load cell I can simply connect the input of the load cell to any DC supply voltage, 15VDC or lower, than measure the output voltage with a multimeter, than some really simple math will give me the mV/V value. Does that sound like the way to go?


JimTitt


Nov 22, 2011, 3:53 AM
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Re: [USnavy] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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Yep, the calibration software either allows two weights (loads to be applied and then calibrate from these or input two mV/V values and their corresponding loads (normally from a cell calibration certificate). The recommended values are something like 25% and 75% but it says somewhere in the manual.

I used weights as Iīve got them (a handy 2 ton block!) but the other way if youīve already another calibrated cell is just put the two cells in line and pull them or if youīve only one cell pull it to a load with the calibrated conditioner, change to the USB adaptor and input the load.


USnavy


Nov 22, 2011, 9:46 AM
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Re: [JimTitt] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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JimTitt wrote:
Yep, the calibration software either allows two weights (loads to be applied and then calibrate from these or input two mV/V values and their corresponding loads (normally from a cell calibration certificate). The recommended values are something like 25% and 75% but it says somewhere in the manual.

I used weights as Iīve got them (a handy 2 ton block!) but the other way if youīve already another calibrated cell is just put the two cells in line and pull them or if youīve only one cell pull it to a load with the calibrated conditioner, change to the USB adaptor and input the load.
I thought the mV/V value was completely linear through the entire range of the load cell, so if its a 3 mV/V step, its 3 mV/V unloaded or at 100% rated load. Is this not true? I was expecting I could obtain this value with it unloaded using a multimeter. Well I dont know how I can calibrate it if I have to use weights, I dont have a 2,500 lb or 7,500 lb weight and I surely dont have anything to lift it off the ground, I would need an industrial overhead crane to lift that type of weight. FrownFrown


(This post was edited by USnavy on Nov 22, 2011, 9:47 AM)


JimTitt


Nov 22, 2011, 10:05 AM
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Re: [USnavy] Looking for software based strain guage indicator/ conditoner. Anyone know of one? [In reply to]
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Unlikely itīs linear because the stretch of the load cell probably isnīt, no idea about the strain guages themselves themselves but probably the change in resistance is a square law since it is relative to the change in cross sectional area (perhaps!).

I use an excavator to lift the weight but thatīs because itīs parked outside!

If you canīt get to someone to calibrate or with a calibrated puller (like an industrial rigging company) you have to go back to the good old lever. You need a long steel girder, a pivot on the end and a known weight (water drums are good as you can accurately measure the volume), a tape measure and away you go. This sounds crude but it isnīt, effectively its how the older Instron testers worked.
Or buy a load cell with a certificate!


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