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ADS1120: Sensor Detection

ttd
Mastermind 8630 points
Part Number: ADS1120


Tool/software:

Dear Technical Support Team,

My configuration is 3-wire RTD with ADS1120.

I have some questions.

Q1)

When it is shorted circuit or open circuit condition, is it possible to measure some kind of temperature?
If so, what is the temperature(code)? Is there any risk then?

I'd like to confirm that I  can detect open / short without BCS or not. 

Q2)

When BCS is enable with 3-wire RTD, set only following bit?

Then my understanding is that open condition shows fullscale code and shorted condition shows zero.

Q3)

Is it disable some register about 3-wire RTD?
If you you have procesure to change from 3-wire RTD measument to BCS, please let me know.

P.S

As backbround, I'm considering to use contact switch insted of 3-wire RTD and detects on(shorted) and off(open). 

Best Regards,

ttd

  • 0
    TI__Prodigy 320 points

    Hello TTD,

    My name is Henry.  I'll be happy to help and thank you for your question.  Please, allow me to respond within a couple of days.

    Best Regards,

    Henry Sarmiento 

  • 0 in reply to Henry Sarmiento
    Mastermind 8630 points

    Hi Henry,

    Do you have any update so far?

    Best Regards,

    ttd

  • 0 in reply to ttd
    TI__Prodigy 320 points

    Hello TTD,

    Thank you for your patience.  I am working however and will provide answers later today though.

    Best Regards,

    Henry Sarmiento

  • 0 in reply to Henry Sarmiento
    TI__Prodigy 320 points

    Hello TTD,

    Thank you for your patience.  Please, see my response to your questions below:

    Q1)  A short or open circuit at your RTD will not measure temperature.  However, a short circuit should produce a small output code and an open circuit should produce a larger output code or full-scale code.  Therefore, BCS will allow you to detect the short or open RTD.

    Q2)  Yes, you are correct:

    • Set BCS bit to 1 in configuration register 1 (01h) to check your RTD circuit.
    • Open circuit produces a full-scale reading.
    • Short circuit produces a reading that is near zero.

    Q3) 

    A.  For a 3-wire RTD, you do not need to disable registers. However, be sure to set the four configuration registers to meet your setup if using Figure 77 in your question:

    • Configuration Register 0 (00h) set AINP = AIN1, AINN = AIN0, gain to your specification, and enable PGA.
    • Configuration Register 1 (01h) set the data rate, operating mode, continuous conversion mode, and BCS.
    • Configuration Register 2 (02h) set external reference (REFP0, REFN0), FIR filter configuration, and IDAC current.
    • Configuration Register 3 (03h) set IDAC1 = AIN2 and IDAC2 = AIN3.

    B.  Use the WREG (0100 rrnn) command to set BCS in Configuration Register 1 (01h). Where configuration register rr = 01 and byte count nn = 00.

    C. To learn more about how to detect a wire-break in an RTD circuit, see application note at the link below:

     

    Best Regards,

    Henry Sarmiento