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XTR115: Increasing current equation.

Ulmus
Prodigy 10 points
Part Number: XTR115
Other Parts Discussed in Thread: XTR111, XTR200,

Tool/software:

Hi, 

i am designing 4-20mA loop with loc111 linear optocoupler. 

Assuming the optocoupler has a minimum coupling coefficient, I can obtain an output current of 80uA, which I apply to the XTR input, pin 2. To obtain a loop current of 25mA, I need a coefficient of 300 rather than 100. I would like to do this by adding a suitable resistor in parallel to the 25 ohm resistor between pins 3 and 4. Has anyone tried this?

  • 0
    TI__Mastermind 27420 points

    Hi Ulmus,

    I've never seen anyone attempt this before. And unfortunately, even if you could do this, we won't be able to guarantee the device performance as it was never characterized in such conditions. 

    We do have 4-20mA current transmitters that have variable transfer functions. XTR111 and XTR200 both have the following equation: 

    Now both of these devices are 3-wire transmitter versus the XTR115 2-wire so there's some major design considerations. 

    Let me know your thoughts. 

    Best Regards,

    Robert Clifton