Overview
The ABB PM851A 3BSE066484R1, also cataloged as the PM851A Processor Unit, operates as a dedicated hardware component for control execution, application processing, and communication management within ABB AC 800M and System 800xA platforms.
Hardware Specifications
| Parameter | Specification |
|---|---|
| Model | PM851A 3BSE066484R1 |
| Brand | ABB |
| Origin | ABB AC 800M series |
| Product Type | Processor Unit / Controller Module |
| System Platform | AC 800M / System 800xA |
| Processor Type | MPC860 |
| Clock Frequency | 24 MHz |
| Performance | 0.46 ms per 1000 boolean operations |
| Memory | 12 MB |
| RAM Available for Application | 6.253 MB |
| Flash Memory | Yes |
| Flash PROM for Firmware Storage | 2 MB |
| Redundancy Support | No |
| High Integrity Support | No |
| Number of Applications per Controller | 32 |
| Programs per Application | 64 |
| Diagrams per Application | 128 |
| Tasks per Controller | 32 |
| Number of Different Cycle Times | 32 |
| Minimum Application Cycle Time | Down to 1 ms |
| Power Supply | 24 VDC (19.2 to 30 VDC) |
| Power Consumption | 180 mA typical / 300 mA maximum at +24 VDC |
| Power Dissipation | 4.32 W typical / 7.2 W maximum |
| Backup Battery | Lithium 3.6 V |
| Ethernet Interface | 1 x Ethernet IEEE 802.3, 10 Mbit/s, RJ-45 |
| Control Network Protocol | MMS and IAC |
| RS-232C Interfaces | 2 ports |
| CEX Bus Communication Modules | 1 |
| CEX Bus Supply Current | 2.4 A |
| Modulebus I/O Capacity | Maximum 24 I/O modules |
| Modulebus Scan Rate | 0 to 100 ms depending on I/O configuration |
| Ethernet Control Network Backbone | Recommended 100 Mbit/s switched Ethernet |
| Real-Time Clock Stability | 100 ppm |
| Operating Temperature | 0 to +55 deg C |
| Storage Temperature | -40 to +70 deg C |
| Relative Humidity | 5 to 95 %, non-condensing |
| Protection Class | IP20 according to EN 60529 |
| Dimensions | 119 mm W x 186 mm H x 135 mm D |
| Weight | 1100 g including base |
ABB AC 800M Controller Communication and Firmware Architecture
The PM851A uses the MPC860 processor architecture to execute IEC 61131-2 based control applications within the AC 800M controller platform. It manages application tasks, program execution cycles, and Modulebus communication between the controller and connected I/O modules.
Furthermore, the processor unit provides Ethernet communication through an IEEE 802.3 interface and supports MMS and IAC protocols for control network data exchange. The integrated flash memory stores firmware data, while the internal lithium backup battery maintains controller clock information during power interruptions.
The PM851A supports firmware flash compatibility functions within the AC 800M environment. Therefore, system engineers can manage controller software updates while maintaining the defined application configuration and communication parameters.
The controller supports industrial I/O expansion through Modulebus. It can manage up to 24 I/O modules, while the Modulebus scan rate automatically depends on the connected module quantity and application configuration.
Frequently Asked Questions
Q: Does the ABB PM851A support controller redundancy configuration?
A: No. The PM851A is specified as a non-redundant processor unit and does not provide redundant CPU switching functions.
Q: What communication interfaces are integrated into the PM851A?
A: The module includes one Ethernet interface, two RS-232C interfaces, and one CEX bus communication connection for AC 800M system integration.
Q: What is the maximum I/O expansion capability of the PM851A?
A: The controller supports up to 24 I/O modules through the Modulebus interface. The actual scan performance depends on the connected I/O configuration.
Field Installation Guidelines
Install the PM851A on the designated AC 800M controller base according to ABB installation procedures. Verify that the 24 VDC supply voltage remains within the specified operating range before applying power.
Maintain proper grounding practices for the controller cabinet. Connect protective earth according to industrial control panel standards and separate signal wiring from high-voltage power cables to reduce electrical interference.
Use shielded communication cables for external interfaces where required by the installation design. Terminate cable shields according to the cabinet grounding scheme and avoid unnecessary cable loops near communication ports.
Confirm that environmental conditions remain within the specified temperature, humidity, vibration, and pollution limits before commissioning. Check Ethernet, RS-232C, and Modulebus connections before downloading controller applications.
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