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AFE4300EVM-PDK: AFE4300 weight measure

Hee-Choel Hwang
Prodigy 45 points
Part Number: AFE4300EVM-PDK
Other Parts Discussed in Thread: AFE4300,

Hi..

I have AFE4300 EVM.

and i connect load cell with EVM.

I put on 20Kg iron.

MSP430 MPU fw is used with TI Download site.

I send command "start?"  then i check uart and lcd.

but always scale weight is 0 and ADC output is low.

- wtAvgOffsetValue =     000000654

- wtWeightValue =     000000000

In The AFE4300EVM-PDK_FW_SRC_Release source is some calculation for weight.

Can i use this calculation OK???

I want know how to calculate.

Thanks a lot.

  • 0
    TI__Mastermind 49666 points

    Hello Hee-choel.

    The AFE needs to be configured before making any measurements.

    You can use the EVM and the GUI directly for these measurements. It is not automated though but at least will give you a sense of readings step by step.

    For the weigh scale calibration, you can do a single point calibration with 1 known weight or a 2 point calibration with 2 known weights.

    The typical procedure for calibration is as follows:

     

    1. Measure weigh scale signal chain offset by not placing any weight on the load cells.
    2. For 1-point calibration, place the known weight on the load cells and estimate the weigh scale sensitivity (V/kg).
    3. For 2-point calibration, estimate the slope and constant of the linear equation with the 2 known weights.
  • 0 in reply to Praveen Aroul
    Prodigy 45 points

    Thanks for reply.

    I test using GUI settings. and get commands(register setting command)

    I see that GUI display ADC out(mV) waveform.

    Downloaded FW source is "start?" command. This command  measure weight scale.

    But, GUI is not suport. So, I send  same GUI command  and  "start". This is my question point.

    "start" command is useful command?

    "start? command register setting is not same GUI settings. expetially 0x0D register.(just DAC gain)

    and  there is some calculation formular This formular is OK?

    [your calibration reply Question]

    1. offset is used estimate the weight scale sensotivity(V/kg). right?

    2. when i have offset and sensitivity, how can i calculation?

    Thanks.

  • 0 in reply to Hee-Choel Hwang
    TI__Mastermind 49666 points

    Do not use the 'start' command provided in the firmware. It was written for internal testing and has not been fully validated.

    I would recommend to first use the GUI with the register settings to find out the offset in codes (no weight), then use a known weight to calculate the weigh scale sensitivity (before you calculate the sensitivity, you will need to subtract the offset).

    Below are the register settings that you could start with.

    reg. addr 0x01 = 0x4140 // 128 sps 

    reg. addr 0x02 = 0x0000

    reg. addr. 0x03 = 0xFFFF

    reg. addr. 0x09 = 0x6005

    reg. addr. 0x0D = 0x0000 // offset dac = 0 and pga gain = 1

    reg. addr. 0x0F = 0x0000 // load cell connected to INP1 and INM1

    1. Capture ADC codes without any weight = OffsetValue in volts

    2. Place a known weight and capture ADC value.

    KnownWt in volts = measured ADC value -  OffsetValue 

    3. Sensitivity = KnownWt in volts / known weight.

    4. To calculate the unknown weight, capture ADC value.

    unknown weight = measured ADC value / sensitivity

  • 0 in reply to Praveen Aroul
    Prodigy 45 points

    Thands a lot!!!

    As your description, I test it.

    when i get none weight in volt, i check GUI plot.

    (average V is mabe V= -0.133 )

    and another known weight is same method.

    In Result, i got real weight(kg).

    I have a few Question.

    1. Capture ADC codes without any weight = OffsetValue in vols.

    ==> adc real value = volt value.   Right??

    2. If so, How can I calculate average volts in fw?

    Thanks.

  • 0 in reply to Hee-Choel Hwang
    TI__Mastermind 49666 points

    ADC codes without any weight will be the offset value represented in codes.

    To convert codes to volts, divide the ADC codes by ADC Full scale code, then multiply by reference voltage.

    The ADC codes to votls conversion formula is:

    ADC data (volts) = (ADC codes in two's complement format * Vref ) / 2^16

    where Vref = 1.7V

  • 0 in reply to Praveen Aroul
    Prodigy 45 points

    Thanks for reply.

    I understand all.

    I have last one question.

    When calculate average ADC , How many time added ADC Value and how much time duration?

  • 0 in reply to Hee-Choel Hwang
    TI__Mastermind 49666 points

    Number of samples to average will depend on your application's speed (how fast should the weight be reported) and the SNR requirements.

  • +1 in reply to Praveen Aroul
    Prodigy 45 points

    Thanks very much. ^^