Re: [foxboro] Check against entering ridiculous values

Adam,
The key is the use of a range or Range Variable (Rxy).

The Range Variables (Rxy) parameters are OM objects that contain 3
floating point values.

Rxy[0] - High scale - HSCxy
Rxy[1] - Low scale - LSCxy
Rxy[2] - Change Delta - DELTxy

The DM/FV is smart enough to set the big (double arrow) and small
(single
arrow) ramp buttons to a percentage of the span IF the Rxy parameter is
specified on the tag name, e.g.,

C:B.SPT|RI1

Might be used for a PIDA block setpoint ramp.


If the Rxy parameter is not specified, a default is assumed and the RAMP
Buttons will use a percentage of that span.

If you want a custom span, you can specify it as follows:

C:B.P|R=<lowRng>,<hiRng>


So, try this:

Make a graphic that contains a rectangle. Configure the select action
ramp with the following line:

C:B.SPT|R=2.0,98.0

Protection Class: 0

+/- percent control range: 5

Where C:B.SPT refers to some PID block setpoint in your system.

This configuration will clamp the .SPT between  2.0 and 98.0 Obviously,
the custom range should be within the block's RI1 (LSCI1,HSCI1)

****** Thanks to Leo Moramarco/FoxCanada and Ignacio Queirolo
Olivera/Repsol for some of the material above.


Regards,
 
Alex Johnson
Invensys Systems, Inc.
10900 Equity Drive
Houston, TX 77041
713.329.8472 (voice)
713.329.1700 (fax)
713.329.1600 (switchboard)
alex.johnson@xxxxxxxxxxxxxxxx

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Adam.Pemberton@xxxxxxxxxxxx
Sent: Monday, October 16, 2006 4:51 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Check against entering ridiculous values

Thanks Rocco
   I wasn't aware of the SPHLIM and SPLLIM parameters and so thank you.
A bit embarrassing really. I thoroughly checked out the PID but not the
PIDA. 

However in this case these limits won't be enough on there own since the
issue with the autoclaves is that the required setpoint range is quite
high, but the short term change must be limited.

   I like your two possible options, that of 1) limiting the setpoint
based on prevailing conditions and 2) using a special overlay. 

I can see how to limit the setpoint but don't know how to implement this
special overlay. Could you please elaborate? I guess I can't see where
the checking code would go.

 

Regards

Adam

 

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Penndorf, Rocco (RP)
Sent: Monday, 16 October 2006 4:05 PM
To: 'foxboro@xxxxxxxxxxxxx'
Subject: Re: [foxboro] Check against entering ridiculous values

 

 

Adam,

 

there are certainly some options how to accomplish this. The most simple
one might be to clamp the range (using SPHLIM, SPLLIM parameters of
PIDA) where you can enter a setpoint. But this approach does not provide
much flexebility in terms of operation of this controller. On some
occurances you might want to be able to enter a very low setpoint, what
is then not possible. 

The second option takes care of this. You also can make this clamp
depending on operating conditions, but this would require an additional
CALC block, what changes the SPHLIM and SPLLIM parameters.

In our plant we are using a special PIDA overlay, what checks if the new
entered setpoint deviates more than 10% from the old setpoint and
notifies the operator.

 

 

Best Regards

Rocco 

 

-----Original Message-----

From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Adam.Pemberton@xxxxxxxxxxxx

Sent: Monday, October 16, 2006 2:04 AM

To: foxboro@xxxxxxxxxxxxx

Subject: [foxboro] Check against entering ridiculous values

 

 

We had an incident on Saturday where an operator accidently entered a
very low setpoint (5kPa when it should be >2200 kPa) on the pressure
control for one of our Autoclaves. This caused the vent valve to open to
100% and the clave to rapidly depressurize. This is a potentially
catastrophic incident since high venting in an Oxygen rich environment
can cause a major fire.

 

 

We are at the final stages of a migration from Display Manager to
FoxView. In order to help these guys with the transition, we have
provided them with one Exceed XTerm running Display Manager off our
engineering development AW.

 

 

 

This incident illustrated a number of issues :

 

   - The operator claimed that the FoxView workstation he was working on
(Blade 150) locked up and he had to move to Display Manager on the Xterm
to correct the erroneous value.

 

   - We have disabled the arrow keys on FoxView while we wait for 9.0.2.
Using the arrows on some parameters gives very large changes.

 

   - We need a good way to prevent ridiculous values being entered in
situations such as this.

 

 

 

My question from all this is what have people in this group done to
resolve the issue of preventing operators from entering dangerous
values? One suggestion was to have a popup appear if the change is
greater than 200kPa (for example). Is there an easy way of doing this?

 

All our workstations are Sun Blade 150's or PC's running Exceed (usually
V7). I/A is version 7.1.1. FoxView is version 9.0.1

 

 

 

Adam Pemberton

Site Electrical & Control Systems Engineer Lihir Gold Limited

 

Ph: +675 9865 655

Fax: +675 9865 666

Mob: Nogat

Postal:

   Australia: GPO Box 905, Brisbane, QLD 4001

   PNG: PO Box 789, Port Moresby, NCD

 

 

 

 

 

 

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Re: [foxboro] Check against entering ridiculous values


 
 
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Systems (formerly The Foxboro Company). Use the info you obtain here at
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_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
 
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