Helo Guys,

For one of my project in control logix 1756-L61 with PV+ in ethernet communication, with devicenet and control net communications to remote devicenet devices and Flex IO's respectively, I want to know whether the selected processor will be suitable to my configuration. Please anybody explain how to estimate the memory requirement so that i can change the processor in early stage itself??????? Can anybody explain me detail with examples???? Please.............................


Thanks in Advance.................................

Cheers ,
TEJ

There are way too many variables. If you don't have any experience with "small" vs. "big", best way to do this is to write the code offline with your selected processor (L61). Watch the estimated memory usage that Logix 5000 calculates. Do this BEFORE you buy the processor. If you need a bigger one, simply select the bigger processor and buy the L63. If you have to budget for it (capital request), then budget for an L63 and buy either the L61 or L63 later when you know what you need.

For the record we were just discussing this in a large chemical plant a couple days ago. None of us has ever run into a memory limit on the L61. We've run into CPU limits (where you have to add a second CPU) but not a memory limit. The memory on an L61 is just so huge that it is not a problem.

The only reason I've seen a memory limit is with online programming. In order to facilitate online programming, you will experience "fragmentation" in your memory...as you make edits and changes, memory usage grows even if you shrink the size of the program over time. The only way to eliminate this is to periodically (say once per year) upload the program and then download it again in offline mode. Then the process begins all over again. A sister plant had multiple PLC-5 programs converted over to ControlLogix and then spent the better part of a year rewriting everything. As they did this they eventually ran into memory limit problems. Once they did an upload/download during a plant shutdown, the problem was solved.

build a project on rslogix add all i/o to the project, ie drives and remot i/o, and local i/o. bring up the controller properties, under the memery tag hit estimate.

Paul mentions lightly what I feel is a very good point. With Ethernet Communication, ControlNet Communication and DeviceNet Communication all occurring with your L61/L63 CPU it is very likely you'll approach what I call the "Operational Connection Count Limits" Please allow me to explain.

1. Every ControlLogix CPU communicates with communication controllers {ENBT, EWEB, CNB, DNB, DHRIO} thru the use of processors connections.
2. There is a hard limit {64,128,256} of the number of connections a CPU can have based on model and firmware. Read the manual for this number.
3. There is a soft limit or "Operational Connection Count Limit" which is somewhat less than the hard limit. Above the Operational Connection Count Limit your system is sluggish and communication is spotty or non existent on some occaisions. There are no hard and fast rules but the CPU and Comm Card manuals give you guidelines to figure these out. The experienced folks here can advise also if you post your plans in general terms. Card Counts, processors etc.

Hope this information is useful. it is worth considering. We have a mixing process which runs off 4 L63's for just this reason. One L61 can hold the code, but performance is unacceptable.