N found this old forum http://control.com/thread/1026157627#1026157627 discussing the difference AB PLC 5 and the Siemens alternative S5; and the comparable difference between the AB Controllogix Gateway and the Siemens S7. Here are some comments that may help to clarify the differences and which solution can be optimal pending your application.
I am not an expert on the referenced product lines, but I think you are comparing apples to oranges, the S7 and PLC5 are different-generation controllers. The AB PLC5 should be compared to the Siemens S5. The Siemens S7 should compared to the AB SLC500 or ControlLogix.
I have no idea how this narrow contest came to be,
but the S7 – AB5 comparison doesn’t pass the smell test.
I suspect there is something that you are leaving
out of this question or your control manager is the owner’s nephew. Just about any PLC can control a handful of external processes in a quasi-concurrent manner. Or did you mean process in a multi-tasking OS sense ?
Scan-time is a function of processor speed, memory
access speed, and bus ( I/O communication ) speed. It would take one sharp cookie to read the specs, even at face value, for a couple of PLCs, and quantify which one of the two is really faster.
Then there is the problem of PLC design, compiled or interpreted, Ethernet/IP or OurBus-OurProtocol
communications, RLL or FBD, and so on.
I know, not a satifying answer, but that’s all I
Why are you using PLC5? I would be more inclined to a newer offering from A-B such as CLogix. S7 and PLC5 are generations apart.
The S7-400 is a super PLC with lots of process capabilities, especially when coupled to PCS-7. However, are you already a Siemens shop? If not then you have to teach all your technicians about OBs, WinCC, Step7, PCS-7 and so on. Plus, PCS-7 has a PCS-7 way of doing things that you are best to follow.
CLogix has an equally capable array of offerings that when coupled to RSBatch, RSView and so on would give you just as good a junior DCS as PCS-7.
If you are an A-B shop, then the leap to CLogix from PLC5 is quite manageable.
I see more of the costs and headaches with intangibles such as support (what time is it in Germany right now anyway?), licensing and so on rather than raw issues such as PLC scan time or the number of PLCs you should be using (independent processes should have their own PLC, don’t be cheap).
Automation Networks ANC Gateway Converter Series has various options interfacing to many factory networks including Allen-Bradley newer Ethernet/IP networks, older PLCs on DH+, and other manufactures such as SiemensProfibus.
One Profibus solution includes:
The Automation Networks ANC-500 PROFIBUS DP-V1 Gateway allows information to be transferred seamlessly between PROFIBUS and RS-485 networks with minimal configuration requirements. The ANC-550 provides a PROFIBUS port (DB-9 female connector) and an RS-485 port (4-wire terminal block style). The RS-485 port supports multiple protocols. PLC-style logical, arithmetic and filtering database manipulation operations allow the construction of complex autonomous data conditioning functions.
|Network Interface||PROFIBUS, RS-485, USB Virtual COM Port|
|Protocols||A. O. Smith AIN Slave, A. O. Smith PDNP Master, BACnet MS/TP Client, BACnet MS/TP Server, DMX-512 Master, DMX-512 Slave, M-Bus Master, Metasys N2 Master, Metasys N2 Slave, Modbus RTU Master, Modbus RTU Slave, Modbus RTU Sniffer, PROFIBUS DP Slave, Siemens FLN Master, Siemens FLN Slave, Sullair Supervisor Master, TCS Basys Master, Toshiba ASD Master, Toshiba Computer Link Master|