We have a situation with multiple (anywhere from 1 to 100) CompactLogix PLC's running practically identical code. Periodically we need to modify one or more setup values in each PLC. All PLC's are networked together (Ethernet/IP) with a central SCADA (Wonderware).
My first instinct is to have the SCADA as a repository for all setup data and push it out to all PLCs when changed, but I was wondering if anyone had any other cunning plans/tools they have used before to achieve this kind of batched data update to multiple PLCs at once.
I've used recipe objects a lot in the past, and they're great for systems where you mostly change the parameters as a set. They protect your operators from small errors, and facillitate changeovers in general. Siemens in particular have a pretty good one in their WinCC Flexible package.
That said, you can write a recipe handler for small systems or for SCADAs where you have to pay (a lot) extra for a recipe management object - I recall that you do pay extra for the Wonderware recipe handler. One way to do this as follows:
1. Define a structure for the recipe information, adding a goodly amount for future expansion. Let's say your normal recipe is 3 floating-point numbers - allocate space for 6, using dummy variables for the remainder. If you ever need to change the recipe, all you have to do is keep the overall recipe size the same (reduce the number of dummy variables).
2. Now, allocate Z x this area in the master PLC, where Z is the maximum number of recipes you would have. These are your stored recipes that can be configured as needed. Each recipe is identifed by a number, 1-Z.
3. Define a "working" recipe that is referenced in the program, and an "temporary" recipe that can be edited without changing a recipe in memory. Add input objects to your HMI recipe screen so the edit recipe values can be edited to your process requirements. You also need a "save" pushbutton to store the values when the operator is done, and a "save to recipe" integer to identify the recipe you want to save the data to.
4. When the operator presses "save to recipe", you can use a block-copy instruction (or whatever your PLC supports for moving memory from one area to another without knowing the format) plus the memory location of the recipe. You will normally have to calculate the address as a number, but this is normally not so hard.
5. Recalling the recipe works the same in reverse - when the operator enters a recipe number and clicks a button called "load", the stored recipe is block-copied to the working area.
6. One last thing - make you you block the operator from changing the recipe when the system is running, and also prevent them changing the running recipe directly in memory.
That might sound a little complicated to describe, but the code is quite simple - I have done this with Rockwell SLCs before, it is probably similar in Controllogix.
