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Original question:

PGA302EVM-037: Could you please tell me the right connection between PGA302EVM and pressure sensor, NPC-100 or NPC-120?

PGA302EVM-037: Could you please tell me the equation between "VINPP-VINPN" and "PDA_DATA1+2 registers data"?

Kazuya Nakai59
Guru 21585 points

Part Number: PGA302EVM-037

 Hello guys,

 One of my customers is evaluating PGA302 using PGA302 EVM for their new products.

 Also they are using the following pressure sensor.

 Amphenor Nova sensor NPC110/120 (Please download from Product Docuemnt tag in the following URL)

 https://www.amphenol-sensors.com/en/novasensor/pressure-sensors/3150-novasensor-npc-100-series-disposable-medical-pressure-sensors

 They have the following questions. Could you please give me your reply?

 Q1. What is the equation between "VINPP-VINPN" and "PADC_DATA1+2 registers data"?

        For example, what is  "PADC_DATA1+2 registers data" when VINPP=1.255V and VINPN=1.250V with P gain=200 and no offset case?

 Q2. Can the offset which the device has be reduced by off set value (-54.75mV~+54.75mV) selecting at "Offset Correction" select window

       on EVM GUI? The customer chaged the value on the GUI. But "PADC_DATA1+2 registers data" was not changed. Do you have any idea about the cause?

 Q3. They want to add offset to data as the follow. Is there any way to realize it in PGA302?

        For example, the follow is in case of no offset.

        A (%)        B (dec)       C (hex)                

1.     100           8191           1FFF

2.     90             6553           1999

3.     50                   0            0000

4.     10           -6554             E666

5.      0            -8192             E000

        A: Input Pressure ratio to NPC110(%)

        B: PADC data in decimal

        C: PADC data in hex-decimal

  They want to add offset to the above data and convert it to the follwing data.

        A (%)        B (dec)       C (hex)                

1.     100           16383           0x3FFF

2.     90             14745           0x3999

3.     50               8192           0x2000

4.     10               1638            0x0666

5.      0                      0            0x0000

 

  Can these data convertion be realized in PGA302?

 If the answer is yes, could you please tell me the way?

 Your reply would be much appreciated.

 Best regards,

 Kazuya.   

  • 0
    TI__Mastermind 31655 points

    Hello Kazuya-san,

    Q1. The output of the PGAIN amplifier is simply the VOUT = (VINPP - VINPN) * GAIN, so a span of 0.005V with a gain of 200, will equal an output of 1V. This will go to the ADC, which will measure between -2.5 and 2.5V, with 16 bits of resolution. This makes the LSB size = 5 V / 2^16 = ~76.29uV. The output code is equal to VIN/LSB size = 1V / 76.29uV = 13107.2 decimal or 0x3333 hex (this is two's complement). 

    Combining everything, the formula is:

    ADC code = ((VINPP - VINPN) * GAIN) / (5 V / 2^16)

    A good reference for calculating ADC codes is shown here: https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2016/04/01/it-s-in-the-math-how-to-convert-adc-code-to-a-voltage-part-1

    Q2. Has your customer placed the PGA302 in reset? If the device is not in reset, no changes to the registers will be made, and the offset correction will not be updated.

    Q3. If the customer completes the calibration procedure, a digital offset will be automatically calculated to cancel any remaining offset in the system. If the customer wants to add additional offset, or adjust the offset that is calculated, they can do so by manually changing the PADC offset value in the EEPROM: 

    Regards,