• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 1489 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1230 & PT100 RTD

Saumitra Deshpande
Prodigy 210 points
Other Parts Discussed in Thread: ADS1230

Hello,

I came across a design idea from Microchip for interfacing PT100 with their 22-BIT sigma-delta ADC MCP3551. Here is the original file.

4643.Mchip_PT100.PDF

Since MCP355x are not easily available here & I do have spare ASD1230s, I decided to experiment with it. Here is my circuit.

1055.ADS1230_PT100.pdf

The issue I am having is, I am not getting expected results. My current test-setup & results are,

D_vdd = A_vdd = 5V, internal osc,

R_rtd = 100E, 1% fixed resistor. 

V_rtd(measured) = 15.3mV

A_ref(measured) = 4.16V

ADC Output(measured) = 7050

With PGA=64, I should get LSB = ((4.16/2)/64)/(2^19-1)  = 61.9889nV, so ADC = 15.3mV/61.9889nV = 246818

Am I doing anything wrong here ? Any help would be great.

Thanks & Best Regards,

Saumitra A Deshpande

  • 0
    TI__Guru** 113765 points

    Hi Saumitra,

    The ADS1230 requires that the input voltage being measured be in the correct common-mode input range.   The restriction is specified on page 3 of the datasheet in the Electrical Characteristics table.  The restriction is 1.5V from either supply rail. Your design has the RTD tied to AGND which is outside the commmon-mode range for the device.The bias resistor RB should be split between RB and RC.  You could split the resistance of RB in half, but to add a little more margin you may wish to make RC slightly larger than RB.

    Best regards,
    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 10 points

    Hello,

    I will be using this IC ADS1230 for a similar application having PT100 RTD sensor at its input. I want to know has this suggestion solved your above problem?


    Regards