Spoiled with Logix5000. Cant figure this out in Logix500

[MorphuisOGrady]

Hi Guys,

Haven't much experience with Logix500 and something I need to do which would be fairly straightforward in Logix5000 is rather difficult in RSLogix500,

I have 30 devices. On Demand I need to turn on the first one and increment a counter associated with it by 1. Then on demand the next one and so forth.

The idea is the one with the least amount of turn ons will start first. A duty rotation scheme of pumps comes to mind.


Anyway in Logix5000 I would have a member of a UDT called TurnOns. Using an array of these objects I would simply loop through looking for an available one with the least amount of turnons.

Is this possible to achieve in RS500 without the use of arrays?

 

[bernie_carlton]

Create a seperate 'N' file. Use indirect addressing to address each. Eg - if N20 is created and N7:10 is the index then use N20:[N7:10] to address the location pointed to by the index. Make sure to not go outside the boundaries of the N file you create.

 

[MorphuisOGrady]

Hi Bernie,

So I create an N file. Lets call it N20. Do i need two N files? One to store the device number and the other to store the No of Activations? There are also some other premissives i need to examine before activation. I.e Available etc.

 

[bernie_carlton]

N7 is a default integer file, it already exists by default. It's a nice place to store all sorts of one-of data items - the the single item I would use as the indirect reference i mentioned - N7:10 (obviously it can be any integer but I'll refer to this location).

I like to keep a set of items I want to access using indirect to their own file. For me I can easily see the limits of the start and stop of the data. Without a special setting going outside those limits generates a great error.

So create N20 (for example) with 30 elements. So you'll have N20:0 through N20:29. These can be accessed as N20:[N7:10] with setting N7:10 to 0 through 29. But don't go to 30. You'll get the error I mentioned.

Also create N21 with the same limits. This is assuming the device number and number of activations are both integers. If the 'device number' will just be 0-29 then they are implied in the setting of N7:10.

UDT's are great in Controllogix and it's difficult to replicate them in RSLogix 500.

 

[MorphuisOGrady]

Hi Bernie,

That makes sense and I understand that all that fine. The problem I'm having is what to store in N20[N7:10]. Is it the number of turn ons?

I need to check a number of things. First is the device available, second has it the least amount of turn ons? If these conditions are satisfied the issue a command to turn on. I fail to see how this can be achieved with 30 elements in an N file.

 

[bernie_carlton]

Let's start with the structure of the UDT you use right now. If 'available' is a BOOL then create a 'B' file and use it in the same way. Let's say you create B22. Use the bits accessed by B22/[N7:10] as the 'available' bits.

So that makes two files, an N file for the number of activations and a B file for the 'available' bits.

 

[MorphuisOGrady]

Ah get you now. Thanks