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Current Loop Control with RS-485/Modbus interface

Former Member

Hi There,

 

I would like to get some recommendations on a new design I am working on. I have never interfaced these current loops and just want to make sure I am going about this in the most efficient manner.  I have the task to create a control board will run a control loop from a 4-20mA sensor to a DSPIC controller and outputs a 4-20mA current loop to control a proportional valve.  The system needs to be able to interface on a RS-485 bus.

 

I have found that there are some pretty nice ICs that contain most of the circuitry to A/D and D/A the current loops.  I have found some interface chips that seem like they will do the job for what I need.  I am hoping to get some feedback for whether these will indeed most efficiently do the job for what I need, or if not I would hope to get some feedback to get me on track.

 

Here are the parts that I am thinking of using:

4-20mA current loop A/D:  AD7707

4-20mA current loop D/A: AD421

RS-485 2 wire transceiver: SN65HVD1782D ( not available through element 14)  Hopefully you can recommend a part from here that will work.

Controller:  PIC33F micro

 

 

Thanks for any insight you may have for me.

.

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  • After looking further into this it looks like the parts that I have chosen are very old.  I am wondering if someone can please fill me in on what the general way that current loops are being implemented these days.

     

    Can someone please list how they would recommend building a current loop receiver and transmitter?  Discrete components?  IC's.

     

    It looks like the receiver end would be straight forward enough using a precision resistor and an opamp?  Can anyone elaborate on any pitfalls associated with this?  What about the transmitter end?

     

    Thanks in Advance.

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  • After looking further into this it looks like the parts that I have chosen are very old.  I am wondering if someone can please fill me in on what the general way that current loops are being implemented these days.

     

    Can someone please list how they would recommend building a current loop receiver and transmitter?  Discrete components?  IC's.

     

    It looks like the receiver end would be straight forward enough using a precision resistor and an opamp?  Can anyone elaborate on any pitfalls associated with this?  What about the transmitter end?

     

    Thanks in Advance.

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