Student in need of some help.

Hello.

I am a student currently working on a DeltaV project at my university where I have encountered a problem.

I am wondering if it is possible to change the I/O cards from Active to passive?

Any information about this would be helpful.

3 Replies

  • Yes, you need 4-wire tx terminal block.

  • In reply to Roman Kostuniak:

    This 4-wire tx terminal block, is this something you program in the software, or is it a physical block you have to connect to the I/O cards?

  • In reply to Sune Hagen:

    Sune,

    I'm assuming, like Roman, that you have a 4-20 mA signal from an externally powered device and you call this a passive signal.  First, this signal needs to be isolated in the transmitter.  That is, the signal circuit must not be grounded in the transmitter.  When you connect this to the DeltaV 4-20 mA input, the circuit will be grounded to the DeltaV ground reference.  If the transmitter signal is not isolated in the transmitter, you will need to use the Isolated Input card or insert an isolator between the DeltaV 4-20 mA input and the transmitter.

    Roman mentioned the 4-wire Tx Terminal block.  If you have M-Series IO cards (Dark Charcoal or black), there is a different Terminal Block assembly for the AI card to support what are called 4-wire transmitters.  These devices provide a 4-20 mA signal to the control system and are powered by some other source, hence the 4 wires.

    I you look in Books Online (Haredware Installation/ M-series Hardware.../Appendix C Interface specs../I/O Cards?...) for the AI card, you can see the diagrams that show the internal connections of the AI card to the two terminal block types.  If you have a mix of 2-wire and 4-wire transmitters, and have two AI cards, you can set one up with the 2-wire Terminal Block and the other with 4-wire Terminal block.

    If you have S-series (Black side panels with a sea foam grey center, black bezel) the AI terminal block comes with three terminals per channel: 24Vdc, Signal, Common.  You can connect either 2-wire or 4-wire devices to any of these channels by connecting to the signal wires to the appropriate terminal.

    If you are on a tight budget, and do not have the 4-wire Block, you can connect the 4-wire device signal to a 2-wire terminal block.  You need to add some standard terminals connected to the DC Common of the bulck power supplies that supply field power to the AI card.  If you look at the diagrams in BOL, you will see that the 4-wire terminal block exposes the DC common.  By adding some terminals you can accomplish the same thing.  You are simply providing a place to land the signal common wire and connecting this to the DC common of the DeltaV system.  Connect the + Signal to the even numbered terminal of the 2-wire Terminal block.  Leave teh 24 VDC (Odd Numberted terminal) unused.  

    Study the diagrams carefully to understand that your common terminals are properly connected and close the circuit in the same way the 4-wire terminal block does.  

    Another approach is to add fused 24 VDC power terminal, with signal and signal common terminals in a marshalling terminal strip.  Connect these 24 VDC fused terminals directly to Field Bulk Power supplies, and use the 4 wire terminal block, connecting the Signal and Signal common terminals to these terminal block.  Now you can connect 2-wire or 4 wire devices to the marshalling strip.  The downside to this is you may have to replace fuses from time to time as you are no longer using the current limited power provided by the AI card.  

    As a studentj, i'd encourage you to explore these options and fully understand the documentation provided with the system.  Good luck.

    Andre Dicaire