Re: [foxboro] FDSI gateway differences again
- From: David Johnson <drjohn@xxxxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Wed, 22 Oct 2008 12:02:26 -0500
At 09:25 AM 10/22/2008, you wrote:
>Why wouldn't you build one DCI block and connect other blocks to that?
>
>Read FDSI --> DCI --> as many input blocks as you like
I'm good with this.
>Write FDSI <-- DCI <-- CALC or SWCH <-- multiple output blocks
OK,
The problem occurs with the following scenario.
Multiple remote modbus devices can write a setpoint (not all visible
to I/A, timing is flaky).
I/A needs to write the setpoint if desired from the I/A screen. The
setpoint is only in one holding register.
The current configuration (I didn't write this) reads the value as an
input then writes it as an output.
AIN [Holding Reg 1] RI01->CALC BLOCK->RO01 AOUT [Holding Reg 1]
Operator Setpoint RI02->CALC BLOCK
Operator Accept BI01 -> CALC BLOCK
So I/A is constantly writing the value to the gateway, if it was
changed remotely, I/A sees and passes this change through. If you
want to change it locally, the operator enters the value RI02, hits
the accept trigger BI01, and CALC BLOCK writes the I/A value until it
sees it come back on the modbus AIN RI01, then it releases it so
other remote locations can set it. This might still work with the
FDSI by just writing the value for some fixed (sufficient) time
period, but operationally it will be different. Currently the I/A
operator is guaranteed that any setpoint change from him will
take. If the loopback is omitted a remote operator could win, (if
the setpoint is changed in the same couple of seconds).
Anyway it's a hassle. Many people (some without meaning to) took
advantage of weird things a gateway could do , and now the FDSI
doesn't allow all of the same tricks.
Thanks,
David
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