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XTR106

mathivanan k
Prodigy 50 points

Other Parts Discussed in Thread: XTR106

dear freinds ,

i have some problem with XTR106 current transmitter .my current output is 13mA to 28mA ,also this is not  linear    but i want linear  4 - 20 mA output ,there is no offset or span options in this ic like  XTR 110. .please help me to get this output , one more thing is  i am using  function generator  for giving input of 0-20mV to the ic  instead of bridge.

  • 0
    TI__Guru 64775 points

    Hello,

    It sounds like you have something connected wrong.  In a properly designed system, a 0V differential input will produce a 4mA output.  Would you please share the schematic for your system so we can look at your configuration and connections? 

    Also, please be sure that the function generator signal is "floating" in relation to the other equipment in the lab.  If the input signal from the function generator shares a GND reference with the loop-supply generator then there will be issues.

  • 0 in reply to Collin Wells
    Prodigy 50 points

    sir ,

    thank you for reply here with i attached the schematic of circuit which i  used , if  any other circuit  ,please suggest me to get 4-20mA output ,for optional.

  • 0 in reply to mathivanan k
    TI__Guru 64775 points

    Hello,

    Some of the schematic is a little hard to read, but I'm pretty sure this is going to be a grounding issue with your signal generator.  The inputs to a 2-wire transmitter must float and if the signal generator GND signal is connected to any potential other than the IRET pin then you will have issues.  Please try to set up a simple circuit such as the ones shown in Figures 1 and 3 and see if your results improve.  Also, please remove the capacitor across the Rg resistor.

    There are several other posts on the forum that deal with issues when not using a floating supply to generate input signals for the XTR devices, try reading over the other XTR posts on the forum.

  • 0 in reply to Collin Wells
    Prodigy 50 points

    sir, instead of function generator i have used quarter bridge also  in that same circuit and i am getting 13-28mA output . i just want to offset the initial current to 4 mA..

  • 0 in reply to mathivanan k
    TI__Guru 64775 points

    Hello,

    What resistor values did you use to construct your bridge?  When you present a 0V differential voltage to the inputs of the XTR106 you're getting 13mA out? 

    It sounds like you still have a connection or other issue that is causing the device to operate inappropritely.  What current are you are you returning into the IRET pin?  If you return more than 4mA into the IRET pin then you will not be able to meet your 4mA zero-scale level. 

  • 0 in reply to Collin Wells
    Prodigy 50 points

    sir i hav used 120 ohm precision  resisters  for bridge,i am getting 0.7 mV ( differential ) output from bridge circuit for  0.7 mV input only  i am getting 13mA output for XTR 106 , the returning current to IRET is 11.8mA  so that only i am getting 12.7mA as per your  previous post , how can i  control the  current to IRET pin???? also now i wired the circuit as per figure 1.......

  • 0 in reply to mathivanan k
    TI__Guru 64775 points

    Hello,

    If you don't have any additional components connected to the VREG or VREF pins of the XTR106 then the current delivered to the IRET pin will be the current dissipated in your bridge.  This current will be VREG / R_Bridge, where R_Bridge is the total impedance located between the VREG and IRET pins. 

    Assuming you've used 4 x 120 Ohm resistors for your bridge, you have a total bridge impedance of (120 + 120) || (120 + 120) = 120 Ohms.  Therefore you are returning at least 5V / 120 Ohms = 41.6mA into IRET which is above the maximum output current of the VREG output which is likely why it seems to be limited to 11.8mA.

    Anyways, your current circuit won't work and you need to increase the resistance of the bridge by adding series resistors and likely a pre-amp as shown in the Figure 5 in the datasheet which I've copied below:
     

    Hope this helps.