Programmable Logic Controllers
Programmable logic controllers split early on control scope, I/O growth, communications, and how much motion or safety logic must stay inside the controller platform. The wrong branch is usually chosen when teams jump into module or part-number comparison before the controller architecture is settled.
In the current catalog, the practical PLC path starts around S7-1200 expansion and adjacent control hardware. Separate compact controller scope, local expansion needs, and downstream I/O direction before narrowing the exact module family.
Current Branches
3 I/O paths
Digital input, digital output, and analog input modules are the active comparison set in the current catalog.
Main Decision
CPU and expansion fit
Controller scope and local expansion needs usually settle the branch first.
Typical Risk
Wrong I/O path
Signal type and channel architecture are often checked too late.
Next Step
Choose module family
Once the PLC path is clear, the module branch becomes easier to read.
Understand the category
Start here to see what belongs in this family, which installation contexts it typically supports, and which brands are represented before you narrow down to a specific series.
What defines this family
Typical environments
Brands in this category
Compare related series
In the current catalog, the comparison set centers on S7-1200 expansion I/O rather than a broad CPU-family matrix. Use the series cards below to separate digital input, digital output, and analog input branches once the controller platform is already narrowed.
That keeps the PLC page useful as a control-direction page instead of a generic controller overview.
| Series | Best for | Deployment | Technology | Compatibility | Lifecycle | Depth |
|---|---|---|---|---|---|---|
S7-1200 SM1221 Digital Inputs S7-1200 digital input expansion family for adding discrete 24 VDC field-signal channels. Open series | S7-1200 stations that need more discrete input channels from switches and sensors. | PLC-side expansion modules for cabinet control panels and machine I/O stations. | DI modules | Best read as the S7-1200 digital input branch before choosing the exact input count. | A standard S7-1200 expansion path for ongoing PLC cabinet work and installed-base support. | 2 products |
S7-1200 SM1222 Digital Outputs S7-1200 digital output expansion family for switching discrete field loads from the PLC. Open series | S7-1200 stations that need more discrete outputs for relays, indicators, or actuator control. | PLC-side output expansion modules for machine panels and control cabinets. | DQ modules | Best read as the S7-1200 digital output branch before choosing the exact output count and type. | A standard S7-1200 expansion path for mainstream discrete control work. | 2 products |
S7-1200 SM1231 Analog Inputs S7-1200 analog input expansion family for process-value and transmitter signal acquisition. Open series | S7-1200 stations that need analog process measurements instead of only discrete I/O points. | PLC-side analog input expansion for cabinet control and process-signal integration. | AI modules | Best read as the S7-1200 analog input branch before choosing the exact channel and signal mix. | A standard S7-1200 path for analog measurement expansion in new and existing panels. | 2 products |
S7-1200 SM1221 Digital Inputs
S7-1200 digital input expansion family for adding discrete 24 VDC field-signal channels.
Best for
S7-1200 stations that need more discrete input channels from switches and sensors.
Deployment
PLC-side expansion modules for cabinet control panels and machine I/O stations.
Technology
DI modules
Compatibility
Best read as the S7-1200 digital input branch before choosing the exact input count.
Lifecycle
A standard S7-1200 expansion path for ongoing PLC cabinet work and installed-base support.
S7-1200 SM1222 Digital Outputs
S7-1200 digital output expansion family for switching discrete field loads from the PLC.
Best for
S7-1200 stations that need more discrete outputs for relays, indicators, or actuator control.
Deployment
PLC-side output expansion modules for machine panels and control cabinets.
Technology
DQ modules
Compatibility
Best read as the S7-1200 digital output branch before choosing the exact output count and type.
Lifecycle
A standard S7-1200 expansion path for mainstream discrete control work.
S7-1200 SM1231 Analog Inputs
S7-1200 analog input expansion family for process-value and transmitter signal acquisition.
Best for
S7-1200 stations that need analog process measurements instead of only discrete I/O points.
Deployment
PLC-side analog input expansion for cabinet control and process-signal integration.
Technology
AI modules
Compatibility
Best read as the S7-1200 analog input branch before choosing the exact channel and signal mix.
Lifecycle
A standard S7-1200 path for analog measurement expansion in new and existing panels.
How to narrow the options
Start with the engineering constraints that actually reduce the option set, then move from those checkpoints into the most relevant series, guides, and tools.
Controller Scope
Decide whether the project still sits inside a compact PLC path or has already moved into a larger control architecture.
Signal Mix and Channel Count
Separate digital input, digital output, and analog measurement needs before looking at exact module codes.
Expansion and Panel Fit
Check how much local expansion, wiring density, and cabinet space the controller branch has to support.
Step 1
Is the main decision still the PLC branch, or only the exact module?
Signals to check
Step 2
What signal family is driving the next purchase?
Signals to check
Step 3
Is this a new panel, an expansion, or a retrofit?
Signals to check
Common selection mistakes
Use this checklist to avoid the common mismatches around compatibility, deployment style, and lifecycle assumptions that usually surface late in a project.
Starting with module part numbers too early
highWhy it matters
Teams compare I/O part numbers before the controller branch and expansion path are settled.
Safer route
Fix the controller scope and signal family first, then move to the exact module series.
Mixing CPU and I/O decisions
mediumWhy it matters
The control platform and the signal-module decision get collapsed into one discussion, which usually creates avoidable rework.
Safer route
Separate controller architecture from I/O branch selection before final module sizing.
Treating all local expansion modules as interchangeable
mediumWhy it matters
Signal type, channel layout, and field wiring expectations often differ more than the part numbers suggest.
Safer route
Use the series layer to separate input, output, and analog module logic before exact MPN comparison.
Frequently asked questions
These answers cover the questions that usually come up after the first pass of comparison and shortlist building.
Next step
Need help narrowing the PLC path?
Share the controller scope, signal mix, and expansion constraints, and we can point you to the right branch before exact module selection.