The PM851K01 is part of the AC 800M controller series, consisting of the PM851 Processor Module and the TP830 Transmission Processor Module. This combination is designed for small to medium-sized control systems, providing complete control processing and communication management functions. The PM851 acts as the main processor, responsible for logic control, data processing, and task scheduling. The TP830 serves as a communication co-processor, handling communication tasks for the ModuleBus and CEX-Bus. Working together, they form a stable and efficient control platform.
The PM851K01 is suitable for industrial applications with high demands for real-time performance, reliability, and cost-effectiveness, such as chemical process control, water treatment systems, energy management, and discrete manufacturing. Its modular design, rich communication interfaces, and good expandability allow it to flexibly meet various complex control requirements.
2. Performance Characteristics Analysis
2.1 Processor and Memory Performance
The PM851 uses a Motorola MPC860 processor running at 48 MHz, paired with 8 MB SDRAM, meeting the real-time requirements of most small to medium-sized control tasks. Its 2 MB Flash PROM stores the firmware, ensuring stable system startup and operation. The memory supports internal or external battery backup, preventing data loss during power outages.
2.2 Communication Capabilities
Ethernet Interface: CN1 provides a 10Base-T Ethernet connection, supporting industrial standard protocols for easy integration into plant information networks.
Serial Communication: COM3 supports multiple baud rates and can connect to modems for remote communication; COM4 is dedicated to local service and debugging.
Bus Expansion: The ModuleBus supports up to 12 S800 I/O units; the CEX-Bus supports communication interface expansion, enabling flexible system architecture.
2.3 Power Supply and Reliability
Wide input voltage range (19.2 – 30 V DC) accommodates industrial site voltage fluctuations.
Internal 5 ms power hold-up time allows the system to perform a controlled shutdown, preventing data corruption.
Redundant power status inputs (SA, SB) can be used to monitor power status, enhancing system availability.
2.4 Storage and Backup
Supports CompactFlash cards for easy application loading and upgrades, and for cold data storage.
Memory backup supports internal battery (≥48 hours) or external batteries (e.g., SB821 ≥1 month, SB822 ≥100 hours when fully charged), ensuring persistent data retention.
2.5 Protection and Environmental Suitability
Protection rating IP20, suitable for installation inside control cabinets.
Complies with industrial electromagnetic compatibility standards, with strong noise immunity.
3. Comparison with Other Models
Within the AC 800M series, the PM851 is positioned as an economical processor. Key differences compared to the PM856 and PM860 are as follows:
Ethernet Ports: PM851 supports only one Ethernet port (CN1), while PM856/PM860 support two (CN1+CN2).
Expansion Capability: PM851 has limited expansion on the Optical ModuleBus and CEX-Bus, supporting a maximum of one cluster or one communication interface.
Execution Performance: PM851 and PM856 have the same execution speed, which is approximately half that of the PM860. That is, if a program runs in time T on a PM860, it will take approximately 2T on a PM851/PM856.
Table 3: Key Differences Between PM851, PM856, and PM860
| Feature | PM851 | PM856 | PM860 |
| Number of Ethernet Ports | 1 (CN1) | 2 (CN1+CN2) | 2 (CN1+CN2) |
| Optical ModuleBus | Max. 1 S800 I/O cluster | Supports multiple clusters | Supports multiple clusters |
| CEX-Bus Expansion | Max. 1 communication interface | Max. 12 communication interfaces | Max. 12 communication interfaces |
| Program Execution Speed | Slower (~50% of PM860) | Slower (~50% of PM860) | Fast (benchmark) |
4. Application Scenarios and Advantages
Applicable Fields:
Process Industries: Chemicals, Pharmaceuticals, Water Treatment
Power Systems: Distribution Automation, Energy Management
Discrete Manufacturing: Production Line Control, Equipment Monitoring
Building Automation: Building Control, Energy Management
Product Advantages:
High Cost-Effectiveness: Meets basic control needs while being more economical.
Modular Design: Supports flexible expansion to adapt to systems of different scales.
Rich Communication: Ethernet + Serial Ports + Buses, supporting multiple integration options.
Data Reliability: Battery backup + CompactFlash storage ensures data security.
Industrial-Grade Design: Wide temperature and voltage tolerance, high noise immunity, suitable for harsh environments.
5. Installation and Maintenance Recommendations
Installation: Should be installed inside a control cabinet with a protection rating of at least IP20, mounted on a DIN rail.
Power Supply: Use a stabilized power supply to ensure voltage remains within 19.2 – 30 V DC.
Grounding: Proper grounding improves noise immunity.
Battery Maintenance: Regularly check backup battery status to ensure data backup duration meets requirements.
Firmware Updates: Can be performed via CompactFlash card or service tools.
