Siemens OCI55 SIGMAGYR Dialogue Operator Interface (Series B) for Landis & Siemens PLC
The Siemens OCI55, part of the SIGMAGYR family, is a dedicated dialogue module and operator interface (also known as Series B) designed for use with Landis & Siemens PLCs and building automation controllers. This compact unit provides a backlit LCD display, membrane keypad, and communication interface for local monitoring, parameter setting, and alarm management. It is commonly used in HVAC (heating, ventilation, air conditioning) plants, district heating stations, and industrial boiler controls.
Display and Keypad Features
The OCI55 features a 4‑line, 20‑character alphanumeric LCD with adjustable contrast and backlight (green). The display can show process values, setpoints, operating modes, and diagnostic messages in plain text. The membrane keypad includes 8 tactile keys: 4 arrow keys for navigation, ENTER, ESC, INFO, and ALARM ACK (acknowledge). The keys are rated for over 1 million operations. The user interface supports multiple languages, selectable via configuration software. A real‑time clock with battery backup timestamps events and alarms.
Communication and Integration
The OCI55 connects to the host PLC or controller via an RS‑485 serial interface (9‑pin D‑sub, electrically isolated). It supports the proprietary Landis & Siemens bus protocol (SIGMAGYR bus) as well as Modbus RTU (slave mode). Baud rates from 1200 to 38400 bps are selectable. The unit can be configured as a remote terminal for up to 31 PLC nodes via multidrop wiring. An auxiliary RS‑232 port (3‑wire) is provided for local configuration using a PC with SIGMADIA software. The dialogue module does not require external power; it is powered from the bus (24 V AC/DC or 230 V AC depending on version – OCI55 typically 24 V AC).
Series B Enhancements
This Series B version (OCI55 / Series B) includes improved processor speed (16 MHz compared to 8 MHz of Series A), increased memory for display pages (up to 128 screens, 64 kB), and enhanced EMC immunity. It also adds a programmable function key (F1) that can trigger macros or force pages. The firmware supports dynamic data display, bar graph representation, and trend curves (historical values stored in the PLC and retrieved on demand). Password protection with two access levels prevents unauthorised parameter changes.
Programming and Configuration
Screen layouts and communication parameters are configured using Siemens SIGMADIA software (version 5.0 or later) running on Windows. The user creates a project defining data points (linked to PLC registers), alarm thresholds, and navigation logic. The configuration is downloaded to the OCI55 via its RS‑232 port. No programming language is needed; a GUI‑based editor is used. The unit also supports hot‑swap of configuration using a removable EEPROM chip (optional). The OCI55 can store up to 200 alarm messages in a non‑volatile log.
Environmental and Physical Specifications
Dimensions: 144 mm × 144 mm × 45 mm (front panel cutout 138 mm × 138 mm). Weight 0.45 kg. The unit is designed for panel mounting (IP65 front protection, IP20 rear). Operating temperature: 0‑50 °C, storage: -20‑70 °C. Humidity: 5‑95% non‑condensing. Power consumption: 4 VA. Electrical isolation: 1500 V AC between bus and front panel. Certifications: CE, UL 508, and EN 60730‑1.
Applications
The OCI55 is typically installed on control panels for district heating substations, chiller plants, air handling units, and small to medium industrial furnaces. It allows operators to adjust setpoints (e.g., supply water temperature), view actual values (flow, pressure, return temperature), acknowledge alarms (e.g., pump failure), and manually override outputs. The dialogue module acts as a human‑machine interface (HMI) for PLCs without a built‑in display, reducing the need for expensive touch panels.
