Compact Logix and Boiler

[Macbeth]

Anyone know if there are issues useing an AB Compact Logix for control of Drum Level make up water on a boiler. I do know it can't be use as flame Guard that will be a fireye.

Customer is looking for us to use AB when ever posable. I am OK with how to program it. My concern is to make sure someone can not say it is not aproved for that type of control.

Oh ya FYI, the level will be 3-element control (Water Level, Steam Flow, Make-Up Water Flow).

 

[controlsdude]

Only issue I have with Compactlogix is the way it uses and processes Analog data.

Its very easy to setup using data in RSlogix5000 when u use a L61 processor. But it is a little difficult when using a Compactlogix. Just beware of the differences and know what they are to begin with.

I would get your area AB rep to go over these diffences.

If you do not know ahead if this has to be a safety plc i would use an L61 processor. Reserve slot 0 for your processor, leave slot 1 as a spare or reserved for just in case you have to switch to a Safety PLC.

If your saying you need it to be Safety PLC then your better off using an L61 off the bat. Reserved slot 0 and 1 for the safety plc in the local rack for use as safety plc.

Look at the Safety PLC devices and IO available. I am sure the local AB rep can go over this with you.

 

[Macbeth]

Dude,

Can ya give a quick example of the difference AB does not seem to know what I was refering to.

 

[dV8r]

Start here.

http://www.gefanuc.com/support

You will find all the manuals and lots of examples. Another good place may be.

http://gefanuc.bnsi.net/eforum/

 

[controlsdude]

Contrologix 1756-L61
The analog scaling, hi, low limits are all setup on the analog card.
Example: Scaling this is a module card property setup
Hi Limit is set in the module card properties
Low Limit is set in the module card properties.
etc....
Nice but you pay for it!!

Contrologix Compactlogix
The analog scaling is setup in ladder logic. The card has no scaling units, no hi limit, no low limit.
This resembles the SLC500, PLC5 legacy setup using ladder logic to do the above that was put into the card

I am shocked that the AB guy locally does not know this. Hey slap him for me.

 

[Macbeth]

dv8r,

Not sure what that is good for?

 

[niallnz]

Hey Controlsdude

Are you saying that macbeth should use a Contrologix for this application, instead of the Compactlogix, just incase he has to convert it into a safety PLC (Gaurdlogix), because the Compactlogix can't be upgraded to a safety PLC?

AB terminology defies logix

 

[controlsdude]

If macbeth sees that the customer requirment is a safety plc for this application then that is the best route. I do not think compactlogix offers the safety plc. check the website and compactlogix is not offered as a safety plc.

There is also the Guardlogixplc that are offered, i can not talk to this product since i have never used it and can not recommend it.

check ab website, see for yourself.

If sil3 is a requirment on this system and there is a product offered that integrates this already and is approved, why would you not use it?

Safety equipment is expensive, getting someone killed is more expensive.

 

[Macbeth]

Dude,

I thought you were indicating that there was a difference on how the cards scanned there I/O. Not the internal scaling. In most cases I have found the Cards Internal scaling to be very limiting. I prefer the use of SCP in most of my projects.

 

[controlsdude]

there is a difference in how a L61 contrologix and compactlogix scans IO.

Contrologix has a seperate processor to scan IO
For the most part you just set rpi locally, if remote racks if using controlnet, its a scheduled network using RSNetworx Controlnet or Devicenet, your choice.

Compactlogix the IO is a priority in scanning IO.

refere to this doc on ab website to get a handle on this.

TasksSchedule 1756-pm005_-en-p.pdf

 

[jde777]

This is incorrect. Compact logix and control logix IO is updated asynchronous to the program scan. In addition the compact logix has a backplane RPI as well as module RPI which is unlike Control logix. And yes some of the analog IO in Compact logix scaling is done in the ladder outside of the module but not all. Also Compact logix is just like Control logix with scheduled connections at some RPI so control on devicenet, controlnet, and ethernet is almost identical. Just remember to inhibit/uninhibit modules in compact logix after configuring since config is only sent to the module on a download or inhibit/uninhibit which is unlike Control logix

 

[controlsdude]

compactlogix
IO is a task at priority 5, if you have an event task it will interrupt the io task, if you have a periodic task that is at priority 1 this will interrupt the IO task.
If you have a continous task this will be interrupted by the IO task.

contrologix L61
this is a seperate processor, there is no task that comes into play when you have tasks such as motion, event, periodic, continuous as stated above.

read the literature I was referring to then you will understand.

yes i would buffer the IO if you dont want it to change during scan time. If this is what your referring to by asynch.

 

[Macbeth]

Ya, it's that inhibit/uninhibit thing that we do not really like. When you have 1637 analog points that are continuously needing verification and scaling needs to be adjusted to match the properties of each device it gets complicated. Having to track each sensor to a channel, each channel to a Slot, Each slot to a rack, each rack to head, each head to PLC, and the green grass grows around and around and the green grass grows around.

It’s much easer to have scaling setup in the HMI then people don’t need to use RS5K.

I do see dudes point on the processor scanning of the I/O but as far as control goes for my application I do not believe scan times are an Issue even if the 5k PLC was 100ms faster the damping on my sensors will be 1-2sec. The logic is really only 3-4 PIDs.

My concerns were really regarding if anyone was aware of code or approval Issues with these products for use in these type applications (Boiler Control).

 

[jde777]

Here is a llink to sample progs for PID and Level control with Compact lgx.

http://samplecode.rockwellautomatio...ount=25&SortField=xSC_Title_EN&SortOrder=Desc

 

[Macbeth]

Those examples are a little simplistic for Boiler Level Control but Thanks for trying..

 

[danw2]

Well, at least Controllogix knows what 3 element control is . ..

http://literature.rockwellautomation.com/idc/groups/literature/documents/br/emse00-br003_-en-p.pdf

 

[mlevesque]

If the Fireye is doing the actual gas valve control/interlock, you can use the ControlLogix or CompactLogix for the other controls within a boiler with no major issues.
If the Fireye is not doing the gas valve control/interlock, you would be better off using a safety controller like the GuardLogix.

Naturally all this depends on your local safety codes, check with the local safety inspector and with the company's insurance company.

 

[PLCMentor]

Macbeth,
The problem being that there is no SCP in the Logix. There is a SCL and it is great - except - it is not available in ladder. I have heard there is a custom block for the ladder that can be added.

Russell

Russell White, P.E.
Automation Technologies, Inc.

http://www.AutomationNC.com

Automation Training

http://www.PLCMentor.com