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BTW

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I have a line set up with a SLC 5/03 and the other racks are connected using an RIO scanner and 1747 ASB adapter cards. In one of the remote racks I have an 8 channel analog card looking at 8 LVDTs. Since I am at a remote location from the main rack I have to use BTR to read the rack,group,slot the analog card is in and write it to an integer file for a length of eight. I seen another line set up like this using a BTW and BTR. The BTW wrote data to each analog channel on the card on the power up scan. My question is do I have to use the BTW on this application and if so could someone explain why.

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guest_Allen_Nelson answered my question in the response to dark dogs question about why he was trying to write data to an analog input card. I didn't realize the NI8 cards had to be configured.

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Refer to A-B's 1747-ASB Remote I/O adapter module user manual. Specialty I/O modules, such as an analog input card, are block-transfer mapped. Whereas, digital I/O modules are discretely mapped. For analog I/O cards, BTW is required to setup the card. The scaling of the inputs, polarity, voltage/current selection, etc., are required to make sure everything talks together correctly. As a rule of thumb, I try to keep high-speed inputs (such as encoders and fast LVDT inputs) in the main PLC rack and digital inputs in the remote I/O drops. This may make wiring cumbersome, but it makes life easier in troubleshooting and programming. Remote I/O is a snail for communication time compared to DH+, DeviceNet or ControlNet. What you can do is add a DeviceNet, ControlNet or ProfiBus card to the SLC-500 rack and run your analog I/O into a FlexLogic or open-ProfiBus drop.

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