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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Safety Integrity Level | SIL 2 (IEC 61508), 1oo1D architecture |
| I/O Capacity | Up to 64 local I/O modules |
| LAN Interface | Dual redundant 10/100 Mbit/s Ethernet (RJ45) |
| Protocol | SafetyNet P2P (Modbus-based, SIL 2) |
| Serial Interfaces | 2 × RS485 (COM1 on carrier, COM2 on controller) |
| Power Supply | 12 V DC from 8913-PS-AC (0.4 A typ., 0.5 A max) |
| Redundancy | Optional with bumpless transfer |
| Configuration | Online via PAC8000 Workbench |
| Event Logging | Up to 8000 events |
| Hazardous Area | Zone 2 / Class I Div 2 (EEx nL IIC T4) |
| Hot-Swap | Yes – live maintainable in hazardous area |
| Dimensions (approx.) | 69 mm (W) × 232 mm (L) × 138 mm (H) |
| Weight (approx.) | 1.35 kg |
4. Product Introduction
The MTL 8851-LC-MT is the SafetyNet Logic Controller for the PAC8000 system. It stores and executes the safety application program downloaded from the PAC8000 Workbench and is certified for SIL 2 applications to IEC 61508 using a 1oo1D architecture with extensive internal diagnostics.
It manages local Railbus communication to up to 64 I/O modules, dual-redundant high-speed Ethernet for peer-to-peer and host communication, and two RS485 serial ports. Optional redundancy provides bumpless transfer for higher availability. The controller supports online configuration, HART pass-through, and event logging of up to 8000 events. It is hot-swappable and can be maintained live even in Zone 2 / Class I Division 2 locations when properly installed.
8851-LC-MT
8851-LC-MT
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| Controller will not power up | Missing or incorrect 12 V supply | ✅ High | Measure 12 V DC at power input from 8913-PS-AC | Verify power supply and connections |
| No LAN communication | Cable, switch, or address issue | ✅ High | Check both Ethernet ports, link LEDs, and IP settings | Test with known-good cable and port |
| I/O modules not recognized | Railbus or carrier problem | ✅ High | Verify carrier power, Railbus continuity, and module seating | Reseat modules and check carrier status |
| Stuck in Failsafe / Safe Mode | Diagnostic fault or application stop | ✅ High | Read diagnostic LEDs and event log | Clear fault via Workbench; investigate root cause |
| Redundancy not transferring | Configuration or cabling mismatch | ✅ Medium | Confirm both controllers see each other on LAN | Verify redundancy configuration and Ethernet links |
| Cannot download program | Workbench version or connection fault | ✅ Medium | Confirm Workbench version and network path | Use compatible Workbench release and correct cable |
If the controller remains in fault after these checks, capture LED status, event log, and configuration details, then contact technical support with photos of the installation.
6. Frequently Asked Questions (FAQ)
Q: What safety level does the 8851-LC-MT achieve?
A: It is certified for SIL 2 applications according to IEC 61508 using a 1oo1D architecture with comprehensive internal diagnostics.
Q: How many I/O modules can one controller support?
A: Up to 64 locally mounted I/O modules on the Railbus, providing over 500 channels per node depending on module type.
Q: Does it support redundancy?
A: Yes. Optional redundancy with bumpless transfer is available for higher system availability.
Q: Can the controller be replaced while the system is running?
A: Yes. It is designed to be hot-swappable and live-maintainable, including in Zone 2 / Class I Division 2 hazardous areas when the installation rules are followed.
Q: What power supply does it require?
A: 12 V DC supplied by the 8913-PS-AC power supply module. Typical current is 0.4 A, maximum 0.5 A.
Q: How is the application program loaded?
A: Via the PAC8000 Workbench software over the Ethernet network. Online configuration and reconfiguration are supported.
Q: Does it support HART?
A: Yes. It provides HART pass-through of process and status variables from compatible I/O modules.
