Product Core Brief
- Model: 3351S2 (AI3351S2)
- Brand: Triconex (Schneider Electric)
- Series: Tricon TMR Safety System
- Core Function: Triple-redundant 4–20 mA analog input acquisition for SIL 3 safety loops
- Product Type: Analog Input Module
- Key Specs: 32 commoned points | 4–20 mA nominal | 12-bit resolution | TMR voting
- Condition: New Surplus / Refurbished options available\
Product Introduction
The Triconex 3351S2 (AI3351S2) is a 32-channel commoned analog input module for the Tricon Triple Modular Redundant safety system. Each of the 32 field inputs feeds three independent signal paths—separate terminal connections, signal conditioners, and A/D converters—before reaching the main processors.
The “S2” hardware revision delivers improved noise immunity and faster internal diagnostic cycles compared to the base AI3351. Voting logic is mid-value selection: the three processors compare the three digital values for each channel and discard any deviating value. This provides hardware-based fault masking without relying on software. The module is SIL 3 certified per IEC 61508 and supports hot-swap in configured Tricon chassis.
Frequently Asked Questions
Q: Can I hot-swap this module while the SIS is online?
A: Yes, in a chassis configured for hot-spare operation. Tricon systems are designed for online module replacement. But two things must be true: the chassis must have a hot-spare slot configured, and you must follow the system executive procedure. After insertion, verify the module is recognized and run a diagnostic cycle before relying on it for safety functions. In our experience, the most common hot-swap mistake is removing a module without first confirming the spare slot is active and healthy.
Q: Is the 3351S2 obsolete? What is the upgrade path?
A: The 3351 family is legacy on older Tricon chassis. Schneider Electric has transitioned newer platforms to updated analog modules. For existing Tricon installations, the 3351S2 remains the form-fit replacement—but you must verify chassis firmware, baseplate type, and TriStation compatibility before ordering. If you are building new, consult Schneider for the current recommended module.
Q: Will I lose my scaling or channel configuration when I replace it?
A: No. Application logic and channel scaling live in the main processors and the configuration database, not in the I/O module. The module itself is a signal acquisition front-end. Before swapping, record the current channel status, engineering units, and any diagnostic states. After installation, force a diagnostic cycle and verify all 32 points report correct values and healthy status.
Q: Are these units genuinely new, or refurbished pulls?
A: Honest answer: the legitimate market for this module is New Surplus and professionally refurbished stock. Triconex modules in this family are no longer in active production. A proper supplier will state “New Surplus Original” or “Refurbished and Tested.” If a vendor claims “factory-new current production” without a clear date code, ask for the label photo. Full functional testing on a Tricon test rack—current injection across the 2–22 mA range, open/short diagnostics, insulation resistance checks—is the minimum bar for a refurbished unit.
