A Unified Platform Approach to OEM Machine Scalability and Brownfield Integration

A machine's control system is an important component of its design and market strategy. Many engineering teams employ a fragmented approach, utilizing multiple PLC families for different machine price points and relying on third-party gateways for integrating legacy systems. This can increase costs related to engineering, inventory, and field support, which in turn can reduce operational agility. An alternative is to standardize on a single, unified platform that can scale across applications and communicate with both modern and legacy protocols.

Using disconnected strategies can be inefficient. Managing multiple PLC families creates logistical challenges in training and inventory, while adding unnecessary hardware, complexity, and potential failure points to the system. But what if a single platform could eliminate these compromises entirely? This article explores such an approach, using the Siemens SIMATIC S7-1200 ecosystem as a case study for addressing scalability and connectivity requirements.

The OEM's scalability challenge

OEM product lines often employ a "good, better, best" model, where machine complexity varies according to the features included. While it makes sense, the challenge lies in specifying a control system that is cost-effective for entry-level models yet capable enough for high-end versions. For this purpose, some of the commonly used solutions are as follows.

1. Multiple control platforms: Using different PLCs for each machine tier may seem cost-effective per unit, but can generate downstream costs in training, programming, and spare parts inventory. This approach forces engineers to become proficient in multiple programming environments and requires a larger, more complex spare parts inventory for both the OEM and the end-user.
2. Oversized and Fixed I/O PLC: Selecting a single, large PLC simplifies programming but can make entry-level models uncompetitive due to the bill of materials (BOM) cost for unused capacity. This approach also offers limited flexibility for future modifications. If a customer requires just one additional sensor, and all fixed I/O points are allocated, a costly and time-consuming redesign may be necessary.

A practical solution is a modular control platform featuring a central processor that can be precisely configured with the I/O required for each machine variant.

Addressing the challenge of brownfield connectivity

How can a state-of-the-art machine communicate effectively on a factory floor built on last-generation technology? This is the core of the system integrator's brownfield dilemma, where new machines using modern protocols, such as PROFINET, often need to integrate with existing equipment that relies on serial protocols, like Modbus RTU. This requires new systems to communicate with legacy VFDs, scales, and other devices over RS-485 serial communication. Two commonly used solutions that address these issues are:

1. Third-party protocol gateways: An external gateway can translate between PROFINET and Modbus RTU, but it incurs additional hardware costs, introduces a potential point of failure, and requires a separate software tool for configuration. Mapping data between the two systems can be cumbersome, and troubleshooting communication issues become a complex exercise in diagnosing two separate devices, often from different manufacturers.
2. Industrial PCs (IPCs) with custom code: An IPC running custom communication software is a capable but costly and complex solution that introduces PC operating system maintenance to the factory floor. This strategy requires specialized IT and software development skills not always present on a traditional automation team and can lead to brittle, difficult-to-maintain solutions.

A modern controller should support legacy communication as a native feature to simplify the architecture and centralize configuration.

A unified solution: The SIMATIC S7-1200 platform

The Siemens SIMATIC S7-1200 series, configured within the Totally Integrated Automation (TIA) Portal, is designed to address these challenges. It provides a cohesive platform with components that offer a range of functions and performance characteristics. Figure 1 illustrates an example of the PLC module controller, highlighting its various components.

Figure 1: A SIMATIC S7-1200 PLC module controller from Siemens consisting of an inbuilt CPU, on-board I/O pins, status LEDs, and connectors. (Image source: Siemens)

The core: a capable, robust, and flexible CPU

At the center of an S7-1200 system is a compact CPU. The CPU 1214C, for instance, has a Boolean execution speed of 0.08 µs/instruction and 100/150 KB of work memory for fast program execution. This is supplemented by a generous 4 MB of load memory to store the entire project (including symbols and comments) and 14 KB of retentive memory to securely save critical machine data through a power cycle. Its integrated PROFINET port supports up to 16 Ethernet connections, functioning as an I/O Controller for a modern field device network, as shown in Figure 2.

Figure 2: Example of a PROFINET IO Controller and IO device topology using SIMATIC CPU. (Image source: Siemens)

Beyond logic, the CPU integrates six independent high-speed counters that can process pulse trains at up to 100 kHz, making them ideal for precise measurement and positioning tasks using encoders. Furthermore, the CPU 1214C features two onboard analog inputs (0-10 V), providing a built-in capability for basic analog sensing without requiring any additional modules. The unit's physical design is built for industrial reality, with a rated operational temperature range of -20°C to +60°C and the ability to withstand vibrations up to 2 g (wall mounting), ensuring reliable operation in demanding environments.

The CPU is available in multiple variants to match any power infrastructure. The 6ES7214-1AG40-0XB0 is a DC/DC model for standard 24 VDC systems, while the 6ES7214-1BG40-0XB0 (AC/DC/Relay) can be powered from a 120/230 VAC source, saving space and cost by eliminating the need for a separate power supply. The 6ES7214-1AG40-0XB0 also features four pulse train outputs for open-loop speed and position control of stepper motors, reducing the need for specialized motion controllers in simpler applications.

Solving scalability with granular, high-performance I/O

A key feature of the S7-1200 is its modularity. The CPU can be expanded with signal boards (SBs) for minor additions and signal modules (SMs) for larger I/O requirements, allowing the BOM to be optimized for the application.

Basic Model: The CPU 1214C’s onboard 14 digital inputs and 10 digital outputs are often sufficient for entry-level machines, providing a cost-optimized starting point.

Mid-Tier Model: To add a 0-10 V analog signal for controlling a variable frequency drive, the signal board SB 1232 >6ES7232-4HA30-0XB0, shown in Figure 3, can be used. It clips directly onto the CPU, providing a single analog output with a 12-bit resolution and an impressive 300 µs conversion time.

This speed is crucial for applications that require responsive control of proportional valves or other analog actuators. The module can drive loads with a minimum impedance of 1000 Ω over a shielded cable length of up to 100 m, adding critical functionality without increasing the controller's footprint.

Figure 3: The SB 1232 - 6ES7232-4HA30-0XB0 signal board for additional I/O for the SIMATIC S7-1200 CPU. (Image source: Siemens)

High-End Model: For controlling a 16-point valve manifold, the signal module SM 1222 6ES7222-1BH32-0XB0 (Figure 4) provides 16 transistor digital outputs, each rated for a robust 0.5 A. A key detail for engineers is the module's built-in limitation of the inductive shutdown voltage to a typical value of (L+)-48 V, which helps protect the outputs from back EMF when switching inductive loads, such as solenoids.

Figure 4: The SM 1222 - 6ES7222-1BH32-0XB0 signal module with 16 transistor outputs featuring inductive shutdown voltage limitation. (Image source: Siemens)

For advanced analog control, the signal module SM 1232 - 6ES7232-4HD32-0XB0 (Figure 5) offers four high-precision analog output channels. Each channel is configurable for either voltage (+/-10 V with 14-bit resolution) or current (0-20 mA with 13-bit resolution). It features integrated diagnostics for electrical faults such as wire-break and short-circuit, allowing the PLC program to detect wiring faults and potential output issues, thereby increasing machine uptime and reliability.

Figure 5: The SM 1232 - 6ES7232-4HD32-0XB0 signal module with analog control integrated diagnostics for Wire-break and Short-circuit faults. (Image source: Siemens)

Solving connectivity with integrated communication

For brownfield integration, the communication board CB 1241 RS485 6ES7241-1CH30-1XB0 plugs directly into the CPU. It provides a physical RS-485 serial port without increasing the system's dimensions, as shown in Figure 6.

Figure 6: Termination and biasing configurations for the RS-485 communication network. (Image source: Siemens)

The port supports communication speeds up to 115.2 kbit/s over a distance of 1000 m. The true integration is in the software. The TIA Portal includes library instructions for not only Modbus RTU (master and slave) but also for Freeport (ASCII) communication, which is ideal for simple devices like barcode scanners, and the USS protocol for communicating with Siemens drives.

Configuration is handled entirely within the TIA Portal project, mapping serial data directly into a PLC data block. This eliminates the need for external configuration tools, simplifying the network architecture. For maintenance, the board includes diagnostic LEDs for transmit (TxD) and receive (RxD) signals, providing an at-a-glance status of communication activity that simplifies on-site troubleshooting.

Conclusion

The primary challenges for automation engineers are managing complexity and designing for agility. Standardizing on a control platform like the Siemens SIMATIC S7-1200 addresses these issues. By combining a capable processor like the CPU 1214C with a flexible ecosystem of modular I/O, from the SB 1232 to the SM 1222 and SM 1232, OEMs can build a single, scalable control architecture suitable for a range of machine price points.

By using integrated communication options like the CB 1241, system integrators can reduce the complexity of external gateways. This unified approach, configured within the TIA Portal environment, can reduce engineering time, minimize inventory, and result in robust and flexible automation solutions.