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PGA309EVM-USB: How to generate a coefficient to correct for nonlinearity

Rui Chen2
Prodigy 40 points
Part Number: PGA309EVM-USB
Other Parts Discussed in Thread: SENSOREMULATOREVM, , PGA309

I recently purchased PGA309EVM-USB and SensorEmulatorEVM. I try to use PGA309EVM to generate a coefficient to correct for nonlinearity.

 

I change necessary jumper to use external sensor. I also input specification of sensor to Generate_Sim_Values.xls and set up sensor emulator according to the following output.

 

 

Here is my connection from sensor emulator to PGA309 testboard,

-+12/-12/GND to external power supply

-Vexc >>>>>>> Vsensor

-Vin+ >>>>>>> Vin2

-Vin- >>>>>>> Vin1

-Buff Temp >>>>>>> Vtemp

-GND >>>>>>> GND

 

I did find Calibration = USB_DAQ + PGA309EVM.ppt on the E2E site about how to setup for calibration. I follow the instruction and

assume is the same for using external sensor emulator. I also uncheck use sensor emulator on create model page. I got the

following calibration info and EEPROM result.

 

 

[General Info]

Date=7/16/2019

Time="9:23 AM"

[Paths]

Model path="/C/Program Files (x86)/proj_PGA309EVM-USB/Model_Files/V_4wire_p5_4p5_test.txt"

Pre-Cal path="/C/Program Files (x86)/proj_PGA309EVM-USB/Pre_Cal_Files/V_4wire_p5_4p5_test.txt"

Sensor Emulator path="<Not A Path>"

[EEPROM Data]

Addr0=21577

Addr2=0

Addr4=0

Addr6=1535

Addr8=28431

Addr10=0

Addr12=5123

Addr14=8869

Addr16=32767

Addr18=0

Addr20=0

Addr22=32767

Addr24=0

Addr26=0

Addr28=32767

Addr30=0

Addr32=0

Addr34=32767

Addr36=0

Addr38=0

Addr40=32767

Addr42=0

Addr44=0

Addr46=32767

Addr48=0

Addr50=0

Addr52=32767

Addr54=0

Addr56=0

Addr58=32767

Addr60=0

Addr62=0

Addr64=32767

Addr66=0

Addr68=0

Addr70=32767

Addr72=0

Addr74=0

Addr76=32767

Addr78=0

Addr80=0

Addr82=32767

Addr84=0

Addr86=0

Addr88=32767

Addr90=0

Addr92=0

Addr94=32767

Addr96=0

Addr98=0

Addr100=32767

Addr102=0

Addr104=0

Addr106=32767

Addr108=0

Addr110=0

Addr112=32767

Addr114=0

Addr116=0

Addr118=32767

Addr120=0

Addr122=17

 

Here are my questions and please correct me if anything I am doing is wrong

1.from old user guide sboa103c.pdf page 40. it talks about generate a coefficient that the PGA309 will use to correct for

nolinearity verses applied pressure. Where can I find this old spread sheet and how can I generate coefficient with the

new PGA309 software.

2.When I connect external sensor emulator with PGA309 to run calibration, do I leave the rotary switch S1 and S2 with no

channel is selected or change S1 and S2 as the calibration runs.

3.After the calibration is finish, it generate a txt file in EEPROM result. but I don’t understand the result. Where can I

find more info about EEPROM data.

 

Thank you,

  • 0
    TI__Mastermind 49475 points

    Hi Rui,

    I am getting a hold of the sensor emulator hardware.  Please allow a couple of days to get back to you.

    Thank you,

    Kind Regards,

    Luis Chioye

  • 0 in reply to Luis Chioye
    Prodigy 40 points

    Hi Luis,

    I still waiting for a response, when do i expect to hear back from you.

    Thank you,

    Rui

  • 0 in reply to Rui Chen2
    TI__Mastermind 49475 points

    HI Rui,

    I apologize for the delay in the response.

    Question 1.

    The spreadsheet calculator mentioned on the Sensor-Emulator-EVM System Reference Guide on page 26-27 "generate_emu_vales.xls" spreadsheet (SBOC065) can be downloaded on the link below:

    http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sboc065&amp;fileType=zip&amp;keyMatch=sboc065&amp;tisearch=Search-EN-Everything

    You will fill in in the spreadsheet calculator the areas in light blue with the sensor specifications and excitation voltage and temperature range requirements.  The spreadsheet generates the sensor output for each pressure point and temperature, as a function of the span, offset, and temperature coefficients that were input into the spreadsheet. You can use the example provided, or you will have to provide this information based on your sensor.

    Question 2.

    2. After adjusting the potentiometers of each bridge pressure/point setting to set the proper voltage output (verified with external meter), you will need to use switch S1 to select the appropriate pressure/temperature point setting bridge as the PGA309EVM GUI steps through each temperature/pressure step during the calibration. You also have to use switch S2 to select the correct ‘Rt’ or ‘diode; temperature point setting (Cold, Room, Hot) depending on the temperature indicated on the PGA309EVM GUI as the software steps through the calibration process.

    Question 3.

    Please refer to the PGA309 User Guide, link is below.

    http://www.ti.com/lit/ug/sbou024b/sbou024b.pdf

    The calibration coefficients are calculated by the PGA309EVM GUI during calibration and stored on the EEPROM along with the PGA309 device settings..

    The PGA309 User Guide on pages 14 shows the EEPROM register contents.

    The first part of the external EEPROM contains the configuration data for the PGA309, with settings for:

    Register 3—Reference Control and Linearization

    Register 4—PGA Coarse Offset and Gain/Output Amplifier Gain

    Register 5—PGA Configuration and Over/Under-Scale Limit

    Register 6—Temp ADC Control

    This section of the EEPROM contains its own individual checksum (Checksum1).

    The second part of the external EEPROM contains up to 17 temperature index values and corresponding temperature coefficients for the Zero DAC and Gain DAC adjustments with measured temperature and contains its own checksum (Checksum2).

    In addition to page 14, section 3.2 on pages 62-70 discuss the EEPROM content and a temperature lookup table calculation example.

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 40 points

    Hi Luis,

    The "generate_emu_vales.xls" spreadsheet (SBOC065) link does not work. I try to search on the website but only find "Generate_Sim_Values.xls".

  • 0 in reply to Rui Chen2
    TI__Mastermind 49475 points

    HI Rui,

    I am attaching the zip file containing the spreadsheet below.  Alternatively, on you could search for SBOC065 on ti.com.

    Please find SBOC065 zip file below.

    sboc065a.zip

    Thank you,

    Best Regards,

    Luis 

  • 0 in reply to Luis Chioye
    Prodigy 40 points

    Hi Luis,

    Thank you for providing the information, it is very helpful. I did enter my sensor specification into light blue area and use sensor emulator to simulate my sensor. But i guess i did not explain what i want to do very well. I would like to use sensor emulator to simulate my sensor and generate coefficient to correct for non-linearity. Then use the coefficient i got from PGA309EVM to enter into real life sensor to correct for non-linearity. how can i found this coefficient? Is that on the EEPROM result? or spreadsheet?

    Thank you,

    Rui

  • 0 in reply to Rui Chen2
    TI__Mastermind 49475 points

    HI Rui,

    The PGA309 device does not store directly the non-linearity coefficient of the bridge sensor.  However, it stores a linearization coefficient (KLIN) which is a function of the reference device, excitation and settings of the PGA309 and a function of the bridge sensor non-linearity.

    Section 2.6.1 of the PGA309 discusses in detail the key linearization design equations and the linearization coefficient (KLIN) on page 33 of the PGA309 User Guide.  The Linearization coefficient is a function of the reference voltage VREF, the excitation coefficient KEXC (scale factor of the reference voltage), the bridge non-linearity with applied pressure (decimal % of full-scale range), and the expected Vout min/max voltages on the PGA309 output corresponding to the min/max pressure applied to the sensor.

    The KLIN linearization coefficient is stored in two's complement format as a function of the Lin DAC settings. Please review (p33-p34) and Example 2-3 (p34-p35) of the PGA309 User Guide for a detailed example. 

    The PGA309 Register 3 contains the reference control and linearization values.  The linearization register 3 is described on section 6.2.4 (p.108 of the user guide).

    The PGA309 Register 3 values are stored on the external EEPROM Address location '1' = 7 and EEPROM address location '0'=6. Consult Table 3-1 of the PGA309 User Guide.

    Hope this helps,

    Thank you and Best Regards,

    Luis