• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 46 subscribers
  • Views 173 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.

DAC161P997: loop output drops to 3,6mA after reaches 16mA

Thiago Pavanelli
Prodigy 10 points
Part Number: DAC161P997

Hello,

I need help with DAC161P997 application:

When I measure the output with an amperimeter it's work well (4 ~20mA), but when I connect with a PLC analog input (120R impedance) DAC output drops to 3,6mA after reaches 16mA.

Can TI team help me with this problem?

Thanks,

Thiago

  • 0
    TI__Guru* 93205 points

    Thiago,

    How do you have the board connected to the PLC analog input? How is the supply connected, and is the PLC analog input at the high side or low side of the board? Can you be detailed in your description? It would help in debugging your connections. 

    I would note that the measurements with the ammeter seem to be ok, so it's likely that the PLC connection has some small error.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 10 points

    This is how I connected my 4 to 20 interface to PLC:

    My supply comes from TR1 (B0303S/D-1W) (Isolated source) 3.3V, changing into an active 4 to 20 circuit.

  • +1 in reply to Thiago Pavanelli
    TI__Guru* 93205 points

    Thiago,


    I think that the problem is that the supply is too low in voltage. This is how I think your circuit is set up in the current loop:

    As you mentioned in the last post, the PLC as an analog input is the equivalent to a 120Ω resistor. The supply is placed in a circuit with the transmitter and the 120Ω in series. If the transmitter is trying to pull 20mA, then the 120Ω resistor itself has 2.4V across it. Because of the voltage drop, the resistor reduces the available operating voltage of the transmitter.

    To check, you should be able to use a multimeter measure the voltages across the resistor and the voltage across the transmitter (and around the board).


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 10 points

    Hi Joseph.

    Sorry for the delayed message, thank you for help me with this problem. This information resolved the issue of my circuit. I changed the 3.3V supply to 5V (isolated supply) and worked.

    Thanks,

    Thiago.