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Original question:

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

AMC1311-Q1: AMC1311 for 4 to 20mAmp current measurement- Circuit Review and Shunt Value

HARANATH VASAM1
Intellectual 300 points
Part Number: AMC1311-Q1
Other Parts Discussed in Thread: AMC1311

As suggested in the thread (https://e2e.ti.com/support/amplifiers/f/14/p/836435/3093804we decided to use AMC1311 for 4 to 20mAmp current measurement. Below is the final schematic, request you to

1) Please review the schematic and suggest changes if any

2) Suggest Rsh value for our below requirement

Input Range:4 to 20milliAmp , DC

Accuracy:0.1%

Sampling Rate:1mS

Test Compliance:EMI/EMC;5kV impulse;2kV dielectric withstand

3)As per AMC1311 EVM, Vout ranges between 0.5V to 2.5V. What are changes to be done to make it 0.5 to 3.3V?

Thanks

Haranath V

  • 0
    TI__Guru 55322 points

    Hi Haranath,

    Nice to hear from you again. I didn't have time to fully simulate the schematic today, but it looks fine for the most part. 

    I have a couple additional questions for you. 

    1. For the shunt resistor size, are you interested in detecting over currents such as shorts, etc? If so, we will need to allow extra range on the input. 

    2. For the output voltage, do you want to be able to sense 0mA (0V output) as well or are you only interested in 4mA = 0.5V & 20mA = 3.3V output?

  • 0 in reply to Alexander Smith
    Intellectual 300 points

    Hi Alex Smith,

    Thanks for the reply. Below are replies to your queries

    1) No we don't want to detect over currents

    2)we are only interested in 4mA =0.5 and 20mA= 3.3V

    Awaiting for your inputs and also complete review on schematic

    Haranath

  • 0 in reply to HARANATH VASAM1
    TI__Guru 55322 points

    Hi Haranath,

    I do not see a way that we can easily make 4mA = 0.5V and 20mA = 3.3V. 

    Is it alright if 4mA = 0.664V?

    Using a 100ohm shunt resistor with a differential to single ended gain stage of 1.65 will make 4mA = 0.664V and 20mA = 3.31V. 

    I've attached a TINA schematic that you can use to play with the resistor values. 

    I do not see the need for the extra buffer that your schematic has. Eliminating this combine with altering the resistor values as shown in the TINA file + a 100ohm shunt should work. 

    Haranath 100ohm.TSC