• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 45 subscribers
  • Views 501 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

ADS124S06: Differential measurement

PLCmatic
Prodigy 90 points
Part Number: ADS124S06

Hi all,

I have a doubt regarding differential measurement with ADS124S06.

Basically I want to measure a DC voltage between AIN1 (configured as positive input) and AIN3 (configured as negative input).The DC voltage to be measured comes from an isolated 4-20 mA transmitter. I want simply reading the voltage due to current across the sense resistor.

The voltage supply of ADC comse from a +12 V flyback converter followed by a low noise +5V_DC LDO. Thus +5V_DC is isolated. ADC reference voltage is directly the +5V_DC.

The high side of the below picture shown the theoretical connection while the low side of the picture show the main connections of the ADC124S06. Since the ground reference of ADC is different from the ground reference of the resistor would the ADC read the DC voltage across the resistor correctly? Should i connect the ground reference of the resistor with the ground reference of ADC? Or maybe may I wrongly connect the ADC for this task?

Thank you in advance for your help.

Best regards

  • 0
    TI__Guru** 113765 points
    Hi PLCmatic,

    As the transmitter can actually float to a voltage outside of the input range of the ADS124S06, you will need to establish a common reference point. This can be accomplished as you have stated by setting the ground reference of the resistor equal to the ADC ground. This will make the measurement single-ended (or 1/2 of the differential measurement) using only the positive full-scale range of the ADS124S06. It appears that you will use 5V for the reference and the maximum output of the transmitter at 4V (20mA * 200 Ohm).

    When making a single-ended measurement with the ADS124S06, you will need to BYPASS the PGA as discussed in the datasheet in section 9.3.2.3 on page 34.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 90 points

    Bob Benjamin said:
    Hi PLCmatic,

    As the transmitter can actually float to a voltage outside of the input range of the ADS124S06, you will need to establish a common reference point. This can be accomplished as you have stated by setting the ground reference of the resistor equal to the ADC ground. This will make the measurement single-ended (or 1/2 of the differential measurement) using only the positive full-scale range of the ADS124S06. It appears that you will use 5V for the reference and the maximum output of the transmitter at 4V (20mA * 200 Ohm).

    When making a single-ended measurement with the ADS124S06, you will need to BYPASS the PGA as discussed in the datasheet in section 9.3.2.3 on page 34.

    Best regards,
    Bob B

    Hi Bob,

    thanks you for the explanation.

    I forgot to mention that the ADC is configured with PGA bypassed as you suggested.

    Thanks again.

    Best regards