Re: [foxboro] INVALM issue on a CIN block -- solved

I agree with the Toms.  IVO should just invert the output of the block; the
existing behavior is incredibly confusing.
I avoid IVO at all costs, and prefer to use INVALM and set NM0 and NM1
accordingly.

Greg Hurwitt
BASF Freeport


Tom VandeWater wrote on 08/23/2008 02:07:39 PM:

> Tom,
>     I strongly agree with your CIN solution below.  In my past
> experience at Dow Corning, and again on the project here in Hawaii we
> decided that using IVO created too much confusion for field
> troubleshooting activities as well as application programming
> understanding.  IMO it could have been more understandable if IVO meant
> Invert Output instead of Invert Option.  If the .CIN (output parameter)
> was inverted instead of making the .IN parameter invert when using IVO
> it would be better.  We got bit here in Hawaii when using the CAPE
> simulator because when IOMOPT is set to 0 for simulation, the block
> functions differently then it does when getting it's .IN value from the
> actual FBM when .IOMOPT is set to 1.  When IOMOPT = 0 the block appears
> to invert the output, (.CIN) based on the opposite value of the .IN
> parameter.
>     Eliminating the use of .IVO and using .INVALM anytime you want to
> alarm when a contact opens in field makes everything consistent across
> the board. In that way SCTXT0 always describes the open field contact
> state and SCTXT1 always describes the closed field contact state.  Since
> .NM1 is always the alarm state text and .NM0 is always the return to
> normal state text the only decision left is whether to set .INVALM to 1,
> (alarm on open contact) or 0, (alarm on closed contact).
>
> Regards,
> Tom VandeWater
> Control Conversions Inc.
>
> Badura, Tom wrote:
> > It sounds like you already have your question answered.  But for what
it
> > is worth we also have a convention with CIN blocks for discrete devices
> > where the block always reflects the actual state of the device (IVO =
0)
> > and then use the INVALM option as necessary to generate an alarm in the
> > proper state.  As such SCTXT0 always describes the Off state, SCTXT1
> > always describes the On state, and NM1 is the In Alarm message and NM0
> > is the Return to Normal message.  Many discrete devices such as level,
> > pressure, flow switches are configured for failsafe operation and we
> > used to use the IVO option; however, our techs and electricians were
> > used to seeing these being On as normal.  Having the CIN block reflect
> > this actual state and just using INVALM to generate an alarm in the Off
> > state has eliminated much confusion.
> >
> > Tom Badura
> > Plastics Engineering Company
> > 920-458-2121 x3366
> > tbadura@xxxxxxxxxx
> >
>

 
 
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