ABB PM851AK01
ABB PM851AK01

ABB PM851AK01 | AC 800M Controller CPU, 24 MHz, 12 MB RAM

  • Model:​ ABB PM851AK01
  • Order Number:​ 3BSE066485R1
  • Brand:​ ABB
  • Series:​ AC 800M
  • Core Function:​ Acts as the central processing unit (CPU) for logic execution, I/O management, and network communication in ABB 800xA control systems.
  • Product Type:​ Programmable Logic Controller (PLC) CPU Module
  • Key Specs:​ MPC860 24 MHz | 12 MB RAM | 24 V DC | Non-Redundant
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Part number: ABB PM851AK01
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Description

Product Introduction

The ABB is a mid-range CPU module within the AC 800M family, designed for medium-complexity process control and automation tasks. It serves as the “brain” of the control node, executing control strategies (PID, Logic) and communicating with S800 I/O modules via the internal ModuleBus.

This unit () includes a TP830 baseplate​ with two RJ45 Ethernet ports and two serial ports. Notably, the PM851 series is a non-redundant​ controller (single unit), meaning it does not support hot-standby CPU pairing like the PM856 or PM866. It is a cost-effective choice for applications where full hardware redundancy is not critical .

 

Key Technical Specifications

Parameter Value
Order Code​ 3BSE066485R1
Processor​ MPC860 (32-bit)
Clock Speed​ 24 MHz
Memory (RAM)​ 12 MB Total (Approx. 6.25 MB avail. for app)
Flash Storage​ 2 MB (Firmware) + CompactFlash Support
Performance​ 0.46 ms / 1000 boolean operations
Power Supply​ 24 V DC (Range 19.2 – 30 V DC)
Power Dissipation​ Typ. 4.32 W / Max 7.2 W
Ethernet Ports​ 2 x RJ45 (CN1 Active, CN2 inactive/restricted)
Serial Ports​ 2 x RJ45 (COM3: RS-232, COM4: Isolated Service)
Redundancy​ Not Supported​ (Single CPU only)
Backup Battery​ 3.6 V Lithium (Built-in, for RAM retention)
Mounting​ DIN Rail (Slide & Lock mechanism)
Protection​ IP20

 

Quality Control Process (Engineer’s Perspective)

  1. Incoming Verification:​ Verify the 3BSE066485R1label matches the laser-etched on the PCB. Check the TP830 baseplate Ethernet label for the unique MAC/Node address. Inspect RJ45 ports for bent pins.
  2. Live Boot Test:​ Seat in a 24 Vdc powered rack. Monitor the “STAT” and “RUN” LEDs. It should pass self-test and reach “Run” mode (or “Idle” if no program loaded) within 30 seconds.
  3. Memory & Storage Check:​ Connect via Control Builder M. Verify the RAM allocation (should see ~6.25 MB free) and attempt a CompactFlash read/write test to ensure the slot contacts are good.
  4. I/O Bus Scan:​ Attach a dummy S800 I/O module (e.g., DI810) on the ModuleBus. The CPU must detect the unit ID without “Unit Failure” errors. Check 24V/5V rail stability with a Fluke.
  5. Final QC & Packaging:​ Check the battery status in software (should be >3.0V). Clean contacts. Wrap in ESD foam with desiccant. Label “QC Passed – Boot Test OK”.
ABB PM851AK01

ABB PM851AK01

Replacement Pitfall Guide

❗ No Redundancy:​ The is Single (Non-Redundant). You cannot pair two of them for High Availability (as you would with PM856/PM866). If the CPU fails, the process stops until replaced. Ensure your HA strategy accounts for this.

❗ Ethernet Port Limit:​ While it has two RJ45s (CN1, CN2), the PM851 only actively uses CN1​ for the Control Network. CN2 is restricted/inactive in this model. Do not design the network expecting dual-port teaming or redundant paths on a single PM851.

❗ Battery Backup:​ The internal 3.6V battery retains RAM data (retentive variables) during power loss. If replacing a faulty CPU, transfer the old CF card​ to the new unit. If the battery died, the RAM data is lost, and the controller will perform a “Cold Start” (may reset setpoints to zero).

❗ Baseplate Compatibility:​ implies it ships with the TP830​ baseplate. Ensure your cabinet DIN rail has space for the combined height (CPU + Base: ~186mm). Mixing with older TP807 bases may require DIP switch re-settings.

❗ Firmware Alignment:​ The new module’s firmware version (e.g., v5.1 FP4) must match the Control Builder M​ project version. A mismatch causes a “Code/Config Mismatch” fault and prevents running.

Keep these in mind and you’ll cut 90% of rework time.

 

Compatibility Matrix & Benchmarks

  • ​ Upgrade​ — PM856 adds Redundancy support (Hardware/CPU level). Requires changing baseplates (TP830→TP831) and project config.
  • ​ Upgrade​ — Significant performance jump (100MHz+ vs 24MHz), adds Redundancy, more RAM. Requires new baseplate (TU8xx series) and project migration.
  • ​ Direct​ — Native ModuleBus communication.
  • Boolean Speed:​ 0.46 ms / 1000 ops (Entry-Mid level performance)
  • Task Cycle:​ Down to 1 ms (Minimum task interval)
  • Event Resolution:​ < 1 ms (SOE – Sequence of Events)

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