Opinion question:

Am in the process of designing a new machine and am torn on which way to go.

System: Rice Lake 920i Weight Controler with printer attached (printer has to go thru 920i to maintain Ntep approval). Attached to the Rice Lake is a Siemens S7-300 PLC (S7-314C-2DP) through Profibus. Valves system is controlling are 3 position valves (Open, trickle, closed) Batch and Bag ID for Printing to come from customer network

Profibus setup: S7-314 Master/ Rice Lake Slave/ MPI to existing network.

Have to use the Rice Lake because this machine has to have NTEP approval. Customer requested the Siemens since it is their standard.

Function: Gain in weight process. Filling a bag from 4 seperate silos controlling a valve for each. Since each valve is a different distance from the bag filler I know I will need a different recipe for each to get the correct weight automatically.

Hopefully that is enough info. Here is my delima. I need to open close and trickle these valves. I have enough I/O to fire the valves from either the Weight Controler or the PLC. The weight control is techincally what sets the valve position but I can use the PLC for this job by sending over status bits thru profibus or as discrete inputs. I am leaning this way. Just wondering someone else would do things different. My main
reasoning is that his should make things simpler and easier to work with.

Looking for opinions here so any are appriciated.

Clay,
It looks like you are filling 1 bag from 4 different silos. It depends on what you are most comfortable with. configuring the weigh scale controller or the PLC. If in fact you have to fill in one place either one will work for you. If you have to fill bags in different places, ie. 4 different silo areas, putting remote I/O at those filling areas would be easier with the PLC because you can put the I/O locally to the fill area. I cant really tell because there isnt enough info. What are you using for the different recipies? an HMI or computer? Vipa has an awesome recipe management software package for their Windows CE touch panels called Zenon. It allows you to import and export recipies with a simple excel spreadsheet. you can get their brochure from here. http://www.vipa.de/en/products/software/hmi-software/

The recipies will reside in the Rice Lake. Basically you have 3 Setpoints. First Setpoint is a say 100 lbs above your tare (tare is created when you press the auto start PB. The first setpoint allows your vibrators to start. The second setpoint will be trickle ( this setpoint is close to your final weight). It shuts down your vibrators and reduces the flow going into your bag. Your third setpoint is where you shut your feed off completely and stop your cycle. This is set to allow for any material remaing in the system after the fill valve to drop into you bag.

On the system I am working on I will have 4 valves (one for each silo). It is with these valves that I control how much material is int the bag. We have only one station for the bag. The tricky part is that we will be running 4 different materials so the flow rates will be different and the distance from the bag which is sitting on the load cells being measured and the 4 feed valves is going to vary from valve to valve.

I am using the Rice Lake to store the recipies in (this is required for NTEP). Depending on which silo is selcted and what weight is wanted to be used decides which recipe is called.

I am not planning on using RIO since the distance is small between the valves and the controler and PLC. I am wondering just if there is some advantage to having the Rice Lake control the outputs directly versus having the PLC. I do not see any myself but Siemens and Rice Lake are 2 platforms that I have limited experience with. I have worked on Profibus networks before but have never created one from scratch. The Rice Lake controlers I have worked with in the past where not as sophisticated as this perticular model.

I was hoping someone has done something similar and would be able to tell me the advantages of either direction.