Allen Bradley vs Siemens PLCs

Allen Bradley vs Siemens PLCs is often a hot debate between the two PLC heavyweights. This is the reason I created this page. I think many of us PLC users out there would like to voice their experience regarding which is better. It could be that there is no clear winner but we aim to find out through the vast experience of all of you may have had in the past or maybe something you are putting together right now.

I recently had attended a Siemens class on the new Simatic Step 7 1200 and came away impressed. I have much more experience with Allen Bradley systems, but this new software has the PLC program, HMI programming, and motion all tightly integrated in one software package. If I had a project that did not have a PLC manufacturer spec I would use this system. I would really like to see how it would function and flow in a real application.

Below are some Allen Bradley vs Siemens PLCs comparisons:

1. Pricing is not always a key consideration, but still a factor. Siemens Safety PLCs are less expensive. Rockwell's Allen Bradley least expensive safety PLC, the Compact GuardLogix, is at a higher entry cost.

2. Siemens PLCs have built-in safety/standard communication ports. Rockwell requires additional cards (Ethernet/IP, DeviceNet.)

3. Siemens does not require a rack or Siemens power supply for the rack, any external 24VDC works. Allen Bradley requires both a Allen Bradley Rack and a Allen Bradley power supply.

4. Siemens supports up to 2 safety runtime groups. This allows the user to implement the safety system at two different time cycles and priorities. For those that find that they have a few safety functions that require a very fast response time within a larger system that doesn't need such a fast response, Siemens easily supports this system. Rockwell has one safety task and cannot establish two priority groups.

5. Rockwell charges for technical support based on the amount of installed hardware. Siemens provides standard technical support at no charge.

6. Siemens supports writing to standard outputs from the safety program. Rockwell does not.This is not a huge item, but if it makes sense to do something such as turn on an indicator light when a particular E-Stop is pressed (or some other function), Siemens supports putting both of these logic elements on the same network in the Safety logic. Rockwell would need to write to the safety output in the safety code, and the standard output somewhere in the standard code.

7. Rockwell provides the safety functions standard with the RSLogix software. With Siemens, Distributed Safety is an add on package with a separate charge.

8. Rockwell's development is perceived by some as intuitive and easy to use.Siemens is perceived as extremely capable, but developed more for engineers than for maintenance and support personnel.

In general, Siemens has always been the technology leader doing the most complex applications and consistently developing new and innovative products. Rockwell's Allen Bradley has always been viewed in the United States as the benchmark for easy to use software.This has to do with the fact that people have been using the software for so long in the United States.
Allen Bradley vs Siemens PLC, which one do you prefer?

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