Analyzing Competing Controller Platforms
September 1, 2010 by admin
Filed under Articles, Controllers, Featured
Webinar will examine Siemens SIMATIC S7-1200 and Allen Bradley MicroLogix platforms.
Electronic system architectures provide different benefits, giving customers alternatives that suit their requirements. Getting an independent analysis of the benefits can help potential buyers determine what the tradeoffs mean to them, but finding third party analysis of industrial systems is sometimes difficult.
An upcoming webinar, An Unbiased Comparison of the Siemens S7-1200 and AB (Allen-Bradley) MicroLogix, focuses on the technology behind these two popular controller platforms. Nick Shea, project engineer for DMC Inc., an engineering and software company based in Chicago, IL, will provide details based on his extensive work with several installations.
“I’ve spent a lot of time over the last several years working with both platforms, and I’ve also worked with a number of customers and software developers who weren’t shy about sharing their views,” Shea says. Before joining DMC, he worked as a machine builder, designing and building custom equipment based on equipment from Allen-Bradley, Siemens and other PLC platforms.
The Webinar, set for Wednesday, September 15, 2010 will examine several aspects as it compares the two platforms. One is the way the controllers manage data memory. Another is the organization of programming routines, and the controller connectivity to other devices.
Keeping memory straight
Memory management can often determine how simple and flexible the automation system will be. This is one topic of Shea’s comparison between controllers like Siemens S7-1200 and Allen-Bradley’s MicroLogix line. Programmable controllers traditionally have dedicated memory for fixed I/O addressing and variable memory for internal program usage. Advancements in controller memory management now include capabilities for tag-based memory enabling the user to assign name designations increasing its flexibility and eliminating the need for users to follow any strict syntax of fixed memory. “The S7-1200 ultimately gives you more flexibility to organize programs and memory the way you want to organize them. MicroLogix provides you with more simplicity,” Shea says.
Shea notes that the approaches are favored by different groups. Those who develop programs often want to organize programs in ways that make sense to them, so they want to organize memory in data blocks. The person who maintains equipment wants data organized in a way that’s logical so they know where to find things in the software. That’s more suited to a memory management schemes that’s based on data types.
Allen-Bradley organizes memory in data files that are unique to data types. All Boolean values are grouped together, as are integers, real numbers and other data types. Users can create several Boolean data files if they find it necessary, and they can also name variables any way they like.
Siemens takes a different approach, managing memory in data blocks. Users can create as many data blocks as they need, filling them with any combination of data types. These data blocks can be given any name users want. “You can mix and match variables, grouping them by functionality, by subsystems of a machine or any sort of functional approach,” Shea says.
Getting organized
In the next factor, program organization, Siemens uses functions and function blocks while Allen-Bradley uses programs for subroutines. Both let developers embed one function within others so one program can call a function or sub function. For example, developers can create a single function block for a motor, using the same block in many programs.
The two companies’ hardware will handle this differently. Siemens hardware handles functions directly, in this example letting programmers use one function block for 100 motors. That makes it very easy to develop programs and keep them up to date.
Allen-Bradley’s programs are organized so that routines will run only once but users will have to create additional memory spaces for each of the 100 motors. “This is easier to read because you’re not using things like multiple instances,” Shea says. “Both vendor’s software allows you to drag and drop icons, so it’s intuitive to drop in parts like coils and contacts.”
While Allen Bradley’s equipment is possibly easier to use for simple applications, Siemens hardware can offer more flexibility for those who need more sophisticated programs. Shea notes that Siemens has made its programming environment much more intuitive in recent years, so the differences between the two have declined dramatically.
We need to talk
Networking is another critical factor as industrial equipment relies more heavily on communication. The shift to Ethernet over the past few years has made network compatibility less of an issue than it was in the field bus days. But that hasn’t stopped developers from pushing technology to make network management simpler.
Many of today’s systems can automatically detect devices attached to the network. They can often figure out important data such as IP addresses and the bus speeds for PLCs and other devices. That makes it very simple to configure networks, add devices and keep equipment humming.
Recently, Siemens added a software feature that helps during setup or when new equipment is added. Its development software can detect new devices before they get an IP address, making it easy to begin communicating with that device without knowing its IP address. Allen-Bradley doesn’t have that feature, although it does provide tools that will assign IP addresses to devices.
There are many factors that determine what architecture will be picked when engineers and designers decide what hardware they want to use throughout their system, or even throughout an enterprise. The Webinar on Wednesday, September 15, 2010 will help users understand the differences between major equipment suppliers so they can make informed decisions.
To register for An Unbiased Comparison of the Siemens S7-1200 and AB (Allen-Bradley) MicroLogix webinar, please click here.
Have an Inquiry for Siemens about this article? Click Here >>
Why can you comparing the recently release Siemens S7-1200 to the ancient micrologix platform. A better comparison would be the the S7-1200 to the ControlLogix or CompacLogix. Although in reality the Rockwell with the symbolic addressing and dynamic memory is far superior to anything Siemens offers. This is only my opinion and I use both platforms.
Since the S7-1200 is the latest and greatest small platform from Siemens, the comparison maybe should be to the Compactlogix. The Micrologix platform has been around close to 15 years, is the same instructions set as the SLC platform which has been out for 20 years, neither of which offer the latest capabilities available from Rockwell. While the comparo may be unbiased, the platforms are not the same technological level. In the end, the CPU choice is normally based on existing installed base and speed of programming, which depends on the programmer’s familiarity with each platform.