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MSP432E401Y: Questions about TI Driver/ADCBuffer Differential functions

Darren Newell
Prodigy 10 points
Part Number: MSP432E401Y
Other Parts Discussed in Thread: SYSCONFIG

I am working to build an RTD interface from scratch as many of the all-in-one solutions are out of stock and I believe the MSP432 should have the ADC resources to handle it. I am working from TI's "A Basic Guide to RTD Measurements" Section 2.4 - Three wire RTD with a single IDAC source, as well as referencing a circuit note from Analog Designs (sorry to mention a competitor)

The two questions I have about the ADCBuffer driver are:

1. Does the "Reference Voltage" option in the Sequencer Channel submenu of the sysconfig for ADCBuffer only affect the "convertAdjustedtoMicroVolts" function output?

2. If I were to set up measurements for three 3-wire RTDs I would need 6 differential pairs - would this be done with 3 ADC buffers, or one ADC buffer with 6 channels of sequencer 0 set up to fill out individual buffers for each differential pair? Could either work?

As a side note, I noticed that adjustRawValues implementation for the MSP432 does not edit any values because there is no calibration feature for the ADC, is my understanding correct? 

I am working off of the example code ADBufDifferential.c to retrieve the voltages from the differential measurement and then carrying out the conversion per the Guide to RTD measurements to end up with a measured resistance for the RTD. With that I plan to use the Callender-Van Dusen equation to retrieve temperature.

My first prototype implementation of this did yield a promising result, but I'm hoping it isn't a fluke.

Many thanks for the support,

Darren

  • +1
    TI__Mastermind 27505 points

    HI Darren,

    1. Yes, the voltage reference for the ADC module can be sourced from the VDD and GND or the external VREFA+ and VREFA-. You can not change the reference voltage by the "Reference Voltage" option. 

    2. I think both the methods would work. 

    Could you point out where you get the "adjustRawValues implementation"? 

    Best regards,

    Cash Hao

  • 0 in reply to Cash Hao11
    Prodigy 10 points

    Hi Cash,

    Thank you for clarifying that the Reference Voltage option does not actually change the physical reference voltage. Is that option used to define a reference voltage somewhere in software for use in a conversion?

    I found the adjustRawValues function is defined under ti\simplelink_msp432e4_sdk_2_40_00_11\source\ti\drivers\adcbuf.

    Best,

    Darren

  • 0 in reply to Darren Newell
    TI__Mastermind 27505 points

    Hi,

    I find this function to convert the result based on the reference voltage. 

    ADCBufMSP432E4_convertAdjustedToMicroVolts()

    Best regards,

    Cash Hao