- Joined Jan 17, 2007
I'd like to sim a load cell circuit using the following example from the AD8221 instrumentation amplifier datasheet:
Welcome to the wonderful world of load cells and strain gauges. With any luck, you'll emerge from this adventure with your sanity intact-- more or less.How much does the upper right resistance shown in the 350Ω bridge varies under normal working conditions?
Thanks for the warm reception... but I've been digging in and out of this subject for a few years already, and I'm afraid to say that the only reason I haven't sought therapy yet is because my medical insurance does not cover this sort of thing.Welcome to the wonderful world of load cells and strain gauges. With any luck, you'll emerge from this adventure with your sanity intact-- more or less.
In a practical application, look for a resistance change of no more than a couple of tenths of a percent, though it depends on the load cell design and the characteristics of the strain gauge bonded to it. Any more than a few tenths of a percent, and for most materials you start getting in the realm of plastic deformation.
Thanks for those two excellent sources of info, C...
I plan to build this thing using a 1.5 mV/V gauge. How do they know that full output from the cell is delivered when the sensing leg drops by 0.8% when the cell is of the 2mV/V type?... a 350 V, 2 mV/V strain gauge delivers full output when one leg drops by 0.8% to 347.2 V
ok ... I know you're not fond of suggesting specific chips when asked ... but here's a question, would that sort of chip have zero-drift capabilities and temperature compensation?Why bother adding pain and torment to your life with analog front-ends? They only add error, noise and drift to an already perfectly good analog signal. Just run the bridge right into a good delta sigma with a built-in PGA and be done with it.
Thank you , Joey... one of the reasons why I was working on the separate components approach was cost. For instance, the AD770 boasts quite a few desirable features, but it's in the range of more than $20 dlls each.I've had great success with the TI ADS1242.
Right... the difference between precision and accuracy is important. Thanks for clarifying.No. High precision.
You'll get 50K divisions without the IA.
Yet another important piece of info, thanks. The specific cell I'll be experimenting with is the LSP-2 from Transducer Techniques:BTW: 50K divisions is very likely far more than your load cell is capable of.
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