[foxboro] Floating point data via FBM 224 - resolved
- From: Gregory A Hurwitt <gregory.hurwitt@xxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Fri, 25 Jul 2008 10:31:13 -0500
Thanks for all the responses on- and off-list. There were four different
solutions proposed, and my final result was different from all of those.
Turns out I just needed to set the SCI correctly in my RIN blocks and then
I was there.
For the record, this is how I have it set up now:
1. In Tricon, set MinSpan and MaxSpan of each real memory variable to the
corresponding engineering unit range. (We already had this set up for our
old communication via Modicon Gateway.) Configure the port on the EICM
that's connected to the FBM224 for a Modbus Range of 0-32767. This setup
will cause the Tricon to automatically scale each floating point
engineering value into the 0-32767 range for transmission over Modbus as an
unsigned integer. This is discussed briefly in the Triconex documentation.
2. In the I/A Modbus Device Configurator, set up a transaction with
Function Code 4 = Read Input Registers. (This corresponds to the 3xxxx
aliases in Tricon.) Starting address is the last 4 digits of the first
alias, e.g., starting address = 3001 for alias 33001.
3. RIN blocks are configured with PNT_NO = nAxxxxU2 where n = transaction
number, xxxx = last 4 digits of alias, and U2 signifies unsigned integer 2
bytes. For example, PNT_NO = 1A3001U2 for transaction number 1, alias
33001.
4. Set RIN block engineering units to match those configured in Tricon.
Set RIN block SCI = 52 to invert the 0-32767 transmission range back to the
engineering units. Done.
Advantage of this method:
- Straightforward. Does not require use of special alias addresses/address
translation or any kind of MGAIN/KSCALE tricks.
Disadvantage of this method:
- Engineering range must be configured (and maintained) in two separate
places.
Original problem post:
>I am trying to read floating point data from a Triconex system (Tricon
>V9.x) with an FBM 224. Data is in Memory/Real/Read-only addresses in the
>Tricon (Modbus alias numbers 33xxx). The "Example for Reading a
>Floating-Point Input" in document B0400FK hasn't been much help.
>The FBM 224 is a new replacement for an old Modicon Gateway 30. Contact
>and integer reads have been tested successfully in the new FBM 224.
>In the old Modicon Gateway, the floating point data has been read using
>SCAN blocks with DATYPE = 4 and BITLEN = 16, and AIN blocks with SCI = 12.
Greg Hurwitt
BASF Corp.
Freeport, TX
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