LOGO! 8 logic modules

What Is the LOGO! 8 Logic Module?

The LOGO! 8 logic module represents a modern evolution in compact automation controllers per Siemens PLC programming basics, designed to replace relay cabinets and conventional switching systems for applications with low to medium control complexity. Its primary role is to provide automation engineers and system integrators a simplified yet powerful programmable relay solution that fits small machine automation, building control, HVAC systems, and retrofit projects where space and cost constraints are critical.

Unlike traditional relay logic panels that rely on hardwired mechanical relays, the LOGO! 8 module consolidates control functionality into a compact device that combines digital and analogue I/O, microprocessor-based logic processing, and integrated communication interfaces. This makes it ideal for discrete logic functions such as sequencing, interlocking, and timing without the need to deploy a full PLC rack.

LOGO! 8 per official specifications offers a diverse lineup of eight base unit variants, covering all common industrial supply voltages, including 12/24 VDC and 115/230 VAC single- and three-phase inputs. This versatility allows seamless integration into almost any industrial or commercial electrical environment without requiring an external power supply or additional hardware.

Hardware Specifications and Available Models

At its core, the LOGO! 8 12/24RCE basic devices family consists of eight basic devices tailored to different voltage requirements and feature sets. Models are available with or without an integrated display for local status indication and operator interaction. The outputs come in two types: relay outputs suitable for resistive and motor loads, or semiconductor outputs (RCSE/RCEO) optimized for high-frequency switching and low electromagnetic interference environments.

Each base unit provides 400 logic blocks of memory capacity allowing execution of complex logic sequences and user-defined functions. The standard configuration includes 8 digital inputs, with four inputs configurable as 0–10 V analogue inputs for more precise sensor integration, and 4 digital outputs. Memory and logic complexity accommodate typical small to medium automation tasks without constraint.

Physical connectivity includes an Ethernet port on every model, enabling integrated communication and remote access capabilities. The hardware is also backward compatible with LOGO! 6 and LOGO! 7 connectors and expansion modules, facilitating seamless upgrades and system expansions without rewiring or hardware replacement.

LOGO! 8 Hardware Specifications Table

Networking and Communication Capabilities

The LOGO! 8 modules integrate advanced networking features that significantly enhance their applicability in modern industrial environments. Every LOGO! 8 unit includes a built-in Ethernet port following industrial network configuration with support for Modbus TCP/IP protocol starting from version 8.1. This protocol enables devices to operate as client or server, making them interoperable with control systems and SCADA environments over standard industrial networks.

Networking capability permits connection of up to 9 LOGO! 8 units, enabling considerably expanded control architectures. This setup supports up to 88 digital inputs, 80 digital outputs, 40 analogue inputs, and 18 analogue outputs system-wide, providing the flexibility required for medium-scale distributed control scenarios without the complexity of larger PLC platforms.

For increased local network connectivity, Siemens offers an optional CSM Ethernet 4-port switch module. This device extends network reach by supporting up to four Ethernet devices with integrated switching, eliminating the need for additional network infrastructure while avoiding consumption of valuable I/O addresses on the LOGO! units themselves.

Integrating LOGO! 8 with SIMATIC Platforms

LOGO! 8 modules provide seamless integration options with the broader Siemens SIMATIC ecosystem. Direct Ethernet communication with SIMATIC S7 CPUs and SIMATIC HMI panels is supported without the need for intermediary gateways, simplifying control system architectures and enabling unified programming environments.

While LOGO! 8 prefers Ethernet as the primary communication backbone, compatibility with KNX and AS-i networks remains available through previous LOGO! 7 modules, providing flexibility in building automation and sensor/actuator integration. Furthermore, enhanced connectivity features like cloud integration through MQTT protocols are included starting with LOGO! 8.4, available after a software activation update, opening pathways to Industry 4.0 and IoT applications.

Display and Operator Interface Options

The LOGO! 8 series emphasizes user-friendly operation with multiple interface choices. Some base units include a six-line display capable of showing 16 characters per line. The display supports selectable background colors—white, orange, and red—allowing visual alarm signaling and easier problem diagnostics on site.

Additionally, an integrated password-protected web server is standard on all models. This embedded server supports remote monitoring and control via WLAN or internet connections using smartphones, tablets, or PCs. The web server requires no HTML coding for custom page creation, improving accessibility for technicians who need quick status checks and parameter adjustments remotely.

Hardware operator control can be enhanced further with LOGO! TDE text displays or SIMATIC Basic Panels, both providing physical HMI capability where local user interaction is essential, such as in critical machine control environments.

Expansion Modules and I/O Architecture

The flexibility of the LOGO! 8 system is exemplified by its modular expansion architecture. Seven digital expansion modules and three analogue modules from the Siemens collection can be connected to a base unit, scaling its I/O footprint from the standard 8 digital inputs and 4 outputs up to a maximum configuration of 24 digital inputs, 20 digital outputs, 8 analogue inputs, and 8 analogue outputs.

Expansion modules can be installed without powering down the base unit, allowing maintenance and upgrades without system downtime. These modules connect via Ethernet interfaces, preserving the base unit's original I/O for production signals and maintaining network communication integrity.

This scalability aligns perfectly with retrofit projects and growing automation requirements, where the initial investment can be modest, yet the system can be extended easily when control demands increase.

Programming Environment and Software Features

Programming the LOGO! 8 logic modules requires the use of LOGO! Soft Comfort V8 or higher versions. This software features a network mode enabling simultaneous editing of up to three programs with intuitive drag-and-drop signal transfers between projects, thereby simplifying complex program management.

Automatic communication configuration within the network view significantly reduces manual addressing tasks and minimizes configuration errors. The software also supports user-defined function blocks (macros), empowering engineers to create reusable logic components that enhance program modularity.

Additional advanced function blocks introduced in version 8 include astronomical clocks, average value calculators, analogue filters, stopwatches, and Min/Max blocks, facilitating sophisticated control and timing strategies within a compact logic environment.

Data logging capabilities allow program data and event timestamps to be written directly to microSD cards, which adhere to standard industrial formats. This data can be used for trend analysis, troubleshooting, or compliance reporting.

Data Logging, Predictive Maintenance, and Power Monitoring

LOGO! 8 logic modules support built-in data logging for collecting operating parameters and event records onto microSD memory cards. This functionality provides valuable insights into system performance and operational history without the need for external data acquisition hardware.

Energy monitoring features integrated within the module enable tracking of electrical consumption in kWh, facilitating demand response management and predictive maintenance. Historical data retrieved from logged information enables identification of trends and early warnings of equipment degradation.

Such diagnostic capabilities extend the value of the LOGO! 8 modules beyond simple control functions into areas that improve plant reliability and operational efficiency, contributing to smarter resource management.

Electrical Details and Output Technology

The LOGO! 8 units cater to a wide range of electrical environments, supporting 12/24 VDC supplies and 115/230 VAC single- or three-phase voltages. The modules feature output technologies suitable for different industrial applications:

• Relay outputs: Electromechanical contacts rated typically at 10 A, suitable for resistive loads and motor controls requiring reliable switching under moderate load conditions.
• Semiconductor outputs (RCSE/RCEO): Solid-state relays designed for fast, high-frequency switching and minimal electromagnetic interference, advantageous in precision or sensitive electronic environments.

Choosing between relay and semiconductor outputs depends on load characteristics, switching frequency, and electromagnetic compatibility requirements of the target application.

Real-World Application Examples

The versatile capabilities of the LOGO! 8 modules lend themselves to numerous practical automation scenarios:

• Machine automation: Implementing sequencing, interlocking, emergency stop logic, and controlled start/stop ramps for small machinery.
• Building and HVAC systems as part of core components of industrial automation: core components of industrial automation Managing thermostat overrides, fan scheduling based on occupancy, and modulating dampers for climate control.
• Energy management: Performing demand response functions such as peak-load shedding and load balancing across multiple equipment to optimize energy consumption.
• Material handling and conveyors requiring motion control systems with PLCs: motion control systems with PLCs Executing speed ramping, accumulation logic, and package sorting or routing for efficient throughput.

Space and simplicity constraints in these applications make the LOGO! 8 a preferred choice over bulkier PLC systems.

Backward Compatibility and Upgrade Path

One of the highlights of the LOGO! 8 series is its excellent backward compatibility with earlier LOGO! 6 and 7 generations. Devices accept connectors and expansion modules from these previous versions, meaning existing customers can upgrade base units without rewiring their established I/O wiring, preserving investment and reducing upgrade labor.

Software-wise, projects created in LOGO! 6 or 7 run on the LOGO! 8 platform when using LOGO! Soft Comfort V8 or later, provided standard validation procedures in the development environment are followed prior to downloading the program to the hardware. This compatibility ensures smooth migration and gradual platform evolution.

Balancing Cost, Complexity, and Performance

LOGO! 8 modules strike a balance suited for use cases where fewer than 50 I/O points and relatively simple sequential logic are sufficient. Compared to starter kits of S7-1200 PLCs, they offer a substantially smaller footprint and reduced setup complexity, reducing engineering time and cost.

The integrated web server, Ethernet connectivity, and remote monitoring features reduce or eliminate the need for purchasing dedicated HMI panels when only monitoring and basic control are required. This characteristic is especially valuable in applications like remote building automation or simple machine controls where investment in a full automation suite is not justified.

Summary of LOGO! 8 Logic Modules in Industrial Automation

Siemens LOGO! 8 logic modules present a compact, scalable, and feature-rich solution for automation engineers and system integrators focused on small to medium control tasks through partners like Leadtime. Their wide range of voltage options, comprehensive I/O expansion, and modern communication protocols provide versatility for complex sequential logic, machine control, building management, and retrofit projects.

Networking capabilities and integration with the SIMATIC ecosystem simplify control architectures and foster efficient resource use. User-friendly programming, real-time data logging, and predictive maintenance features enhance system intelligence and uptime. Together, these factors make LOGO! 8 a compelling choice for numerous industrial, commercial, and OEM applications where space, cost, and simplicity are essential considerations.