• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 47 subscribers
  • Views 1975 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.

AMC1301: AMC1301 for Isolated 4 to 20mA current measurement - Differential Input

HARANATH VASAM1
Intellectual 300 points
Part Number: AMC1301
Other Parts Discussed in Thread: AMC1311

Hi,

Planning to use AMC1301 for Isolated 4 to 20mA current measurement with differential Input. Proposed schematic and Sensor data sheet is attached. Request to confirm whether all connections are correct or not.

Note:

1) GND1 of AMC is NOT connected to IN- 

2) GND1 is not connected to GND of sensor.

Will this work? H72515n_Hybrid_Gas_Density_Monitor_878X.PDF

  • 0
    TI__Guru 55312 points

    Hi Haranath,

    There are a couple issues with this design.

    1. The ground of the AMC device must be connected to the GND of the power supply (which it is) as well as the GND of the field sensor. Without a common GND between the AMC and the field sensor, the input voltage can float out of the common-mode input range. 

    2. The AMC1311 will be a better choice here as the input bias current of the AMC1301 is relatively high. This bias current will impact the accuracy of the measurement. From 4mA to 20mA, it is a span of 16mA. If you accuracy target is 0.1%, then you're looking at 16uA of system error which is less than the 30uA input bias current of the AMC1301. The AMC1311's input bias current is typ 3.5nA. 

  • 0 in reply to Alexander Smith
    Intellectual 300 points

    Hi Alex,

    Thanks for the reply.

    For 2 reasons I have not chosen AMC1311

    1) Datasheet of AMC1311 says '"Phase current measurement is accomplished through the shunt resistors, RSHUNT (in this case, two-pin shunts) and the AMC1301 isolated amplifiers that are optimized for isolated current sensing. " Refer Section 9.2 , page 22 of 36. http://www.ti.com/lit/ds/symlink/amc1311.pdf

    2)Our input is differential and  there is no IN- for AMC1311 , I thought AMC1301 is most suitable.

    Do you still suggest AMC1311 over AMC1301?

    Regards,

    Haranath

  • 0 in reply to HARANATH VASAM1
    TI__Guru 55312 points

    Hi Haranath,

    Happy to help! 

    It's true that the AMC1301 (low input impedance) is optimized for current sensing while the AMC1311 (high input impedance) is primarily used for voltage sensing in high power applications. However, for 4-20mA applications using the AMC1311 makes sense for the difference in bias current that I mentioned in my previous post. 

    The measurement will be conducted with respect to GND. So you would connect the negative output of the sensor to sensor GND, then connect that to the GND of the AMC1311. The positive sensor output will connect to the input of the AMC1311, with the shunt resistor spanning from the input of the AMC1311 to GND.