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ADS1120EVM: Convert electrical signals to torque readings

Drake Burtrum
Prodigy 130 points

Part Number: ADS1120EVM
Other Parts Discussed in Thread: ADCPRO, ADS1220

Hello,

I'm using the ADS1x20EVM Evaluation Module with the ADCPro software. I have a strain gage torsional load cell with a full wheatstone bridge configuration. It looks like the software is getting electrical signals when torque is applied to the load cell. The part I'm struggling with is how to turn those electrical signals into torque readings. I've been saving the data into .txt files and then copy/pasting them into excel to do data analysis. I'm not seeing anything in the data sheets regarding calibrating signals with known weights. I'd be grateful for any insight or guidance in this matter.

Thank you.

  • 0
    TI__Guru 59531 points

    Hi Drake Burtrum

    Is there something specific you are looking for from us? Generally, we rely on you to be the expert regarding your application, and we are the ADC experts.

    But I think in general you would just apply known weights across your measurement range (maybe 0.5kg, 1kg, 5kg, and 10kg for example) , take several measurements per weight to reduce noise, and then that will characterize the sensor response (at least at that specific temperature). Then you could use a look-up table + interpolation or a polynomial equation to determine any new signal you measure. Of course you will need to derive the equation or create the table + interpolation algorithm

    -Bryan

  • 0
    Prodigy 130 points

    Hi Bryan,

    I mostly wanted to ask if there's a best practice for filtering out unwanted data.

    When I apply known weights and run the test plug-ins, it gives thousands of output data readings. I'm struggling with determining which readings are valuable and which are not. 

  • 0 in reply to Drake Burtrum
    TI__Guru 59531 points

    Hi Drake Burtrum

    I guess this depends on what you mean by "unwanted"? Are you trying to remove a specific frequency e.g. 60Hz?

    It sounds like you might also be concerned with how much data you are receiving from the ADC. I don't know that I have an answer for this question, it really depends on what you are trying to do in your system. Some engineers are measuring multiple signals so they take a measurement per channel and then move onto the next channel. Some engineers need to conserve power, so maybe they only take 1 or a few samples every 500ms for example and then the system is put to sleep during the rest of that time. Some engineers continuously convert on a single channel forever, and therefore need to constantly evalute the data they receive at some interval (for example, they take an running average of the last 10x samples)

    Again, there are so many ways to achieve the same goal I don't have any specific method to offer you. It comes down to what is your end goal with the system you are designing

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 130 points

    Unwanted data would just be electrical noise, anything that doesn't directly correlate with the applied load. I'm not looking to remove a specific frequency at the moment.

    That last example sounds close to what I'm trying to do with my application. Does the ADCPro software support constant evaluation of data? 

  • +1 in reply to Drake Burtrum
    TI__Guru 59531 points

    Hi Drake Burtrum,

    Unwanted noise is fairly broad category. Input filtering, supply filtering, practicing good routing and layout techniques, shielded cabling and/or PCBs, etc., will help remove unwanted signals

    The EVM GUI has a # of samples in the top right corner that indicates the number of samples to capture. I am not sure if there is a practical limit to this number, but I would guess there is. Additionally, the EVM is meant as an evaluation platform so it doesn't necessarily support everything you might want the ADC to do. And certainly the GUI won't perform any real-time calculations on the data, averaging, etc., so it probably makes more sense to connect the EVM to an external controller e.g. MSPM0 launchpad, and use our ADS1220 example code as a starting point for your own firmware

    -Bryan