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XTR116: XTR116 full bridge sensor EXC- ground

Ryan Rousseau
Prodigy 20 points
Part Number: XTR116
Other Parts Discussed in Thread: PGA308

Tool/software:

I'm using an XTR116 in conjunction with a PGA308 for 4-20mA conditioning on a full bridge sensor.  All grounds appear to be tied to I-RET except for the EXC- of the full bridge.  I would assume that this EXC- ground (circled in green of attached image, needs to be isolated from the I-RET grounds.  I'm assuming this EXC- ground can just be floating or tied to chassis ground.  Looking for verification that it doesn't need to be somehow tied back to the XTR or PGA grounds.  Thanks! 

  • +1
    TI__Guru 52756 points

    HI Ryan,

    In a 2-wire current transmitter module, the bridge sensor and instrumentation amplifier (PGA308) driving the XTR116 2-wire current transmitter, all need to be referred to the same local ground (IRET). IRET needs to be isolated from the 4-20mA loop supply. 

    Also, on a 4-20mA 2-wire current transmitter application, the total current consumption of the XTR116 + PGA308 + bridge sensor needs to be less than 4-mA.

    Please connect the bridge sensor to IRET as shown on the modified figure below. This is an error on Figure 6-3, and will need to be corrected.

      

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 20 points

    Luis,

    Thank you for the response and clarification, this is very helpful.  This makes more sense to me in terms of how the overall concept works as well.  I was really struggling to come up with a separate chassis ground for it without affecting current drain/offset through the bridge. 

    Best,

    Ryan