Re: [foxboro] "GDEV" or "VLV,MOVLV,MTR" or "CALC" - Discrete control engineering advice ?

  • From: "Wilson, Brad" <brad.wilson@xxxxxxxxxxxxxxxx>
  • To: <foxboro@xxxxxxxxxxxxx>
  • Date: Wed, 1 Aug 2007 11:08:12 -0400

I've used GDEV quite successfully for most apps. Don't forget the STAIND
output which can be used with MMAIND quite effectively to tell you
whether you have a RUN>STOP>RUN state, or a STOP>RUN>STOP state. The
various state conditions can be well-documented by using STATx and MMx
string parameters.

The only device I've been unable to automate with a single GDEV is a
3-position valve (open/partway/close) which we've used to prevent hammer
when closing the valve, or any device that has 3 or more distinct
positions.

Brad Wilson
brad.wilson@xxxxxxxxxxxxxxxx
Invensys Systems, Inc
1090 King Georges Post Rd, Suite 204
Edison, NJ  08837
732-874-0087


-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Corey R Clingo
Sent: Wednesday, August 01, 2007 10:32 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] "GDEV" or "VLV,MOVLV,MTR" or "CALC" - Discrete
control engineering advice ?

We have.

Pros:
---------
1. Consistent operator interface


2. Consistent engineer interface :)


3. Good set of capabilities -- command disagreement alarming, =

interlocking, output readback handling, etc.


4. Most closely resemble (but, alas, do not match in capability) the =

Honeywell digital composite blocks I used pre-I/A.


Cons:
----------
1. Only 2 states.  For motor starting, a third momentary state would be =

nice.  It causes operator confusion at times when they forget that they =

have to make a RUN->STOP->RUN transition to restart a motor that was =

stopped in the field.  You could take care of this probably with some =

logic, but we have not decided to do that yet (that has its own pros and

cons).  I don't think any I/A discrete control blocks have this, though,

so it's not a weakness only of the GDEV.


2. I'm not sure a GDEV would do electric-actuated valves without extra =

logic.  There are two outputs, but I think they are always inverses of =

each other or something (I can't recall ever using COUT_2).  We don't
have =

any of these, so I can't say for certain.  For our standard =

air/solenoid-operated valves and motors, the GDEV works pretty well.


Corey Clingo
BASF Corporation






"Bruley, Peter T" <Peter.T.Bruley@xxxxxxxxxxxxxx> =

Sent by: foxboro-bounce@xxxxxxxxxxxxx
08/01/2007 08:57 AM
Please respond to
foxboro@xxxxxxxxxxxxx


To
"Foxboro@Freelists. Org \(E-mail\)" <foxboro@xxxxxxxxxxxxx>
cc

Subject
[foxboro] "GDEV" or "VLV,MOVLV,MTR" or "CALC"   -    Discrete control =

engineering advice ?





We are in the process of replacing a L&N DCS with a Foxboro I/A DCS.=3D20

------------------------------------------------------------------------
-=3D
-------

We are considering using the "GDEV" block for all our open/close
valves=3D20
(single coil + dual coil solenoid & motor actuated) as well as all
the=3D20
motor start/stop. (instead of using blocks: VLV, MOVLV, MTR)

Who out there has standardized on the "GDEV" block for on/off open/close
=3D
control?

What have you learnt by doing this? What are the advantages? What are =3D
the disadvantages?

------------------------------------------------------------------------
-=3D
------

Another method our Foxboro Engineers have recommended to us is to use =3D
the "CALC" block=3D20
(instead of GDEV, VLV, MOVLV, MTR)

Has anyone gone this route?

What have you learnt by doing this? What are the advantages? What are =3D
the disadvantages?


Thank You,

Peter Bruley

Plant Process Computer Analyst
Xcel Energy - Sherco Generating Plant
Peter.T.Bruley@xxxxxxxxxxxxxx




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