The FX3U-32MT-LT-2 is Mitsubishi Electric’s battery-less 32-point transistor sink output base unit for the MELSEC FX3U compact PLC series, providing 16 digital inputs and 16 NPN transistor outputs with all program and data memory stored in non-volatile flash ROM — eliminating the lithium battery required by standard FX3U models to retain program memory and device data during power outages, dramatically reducing maintenance requirements in applications where periodic battery replacement is impractical or where battery-related maintenance shutdowns are unacceptable. As the battery-less variant of the FX3U-32MT/ESS, the FX3U-32MT-LT-2 is specified for remote, difficult-to-access, or high-ambient-temperature installations where battery maintenance is a significant operational burden. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the FX3U-32MT-LT-2?
The FX3U-32MT-LT-2 is a MELSEC FX3U series compact PLC base unit with transistor sink (NPN) outputs and a battery-less memory architecture. The «LT-2» suffix designates the battery-less transistor output model — all program memory, parameters, and designated data register values are stored in internal flash ROM rather than battery-backed SRAM, ensuring data retention indefinitely without battery replacement. The battery-less design is particularly valuable for installations in high-temperature environments (above 40°C), underground installations, marine applications, and geographically distributed remote stations where on-site maintenance is infrequent and battery failure risk is unacceptable. The FX3U-32MT-LT-2 provides 16 input points (X0–X17) and 16 transistor sink output points (Y0–Y17) with the same 0.065 µs execution speed, 64,000-step program memory, and communication interfaces as the standard FX3U-32MT/ESS — with the sole architectural difference being flash ROM-based memory retention rather than battery-backed SRAM.
Key Technical Specifications
- Model: FX3U-32MT-LT-2
- Total I/O Points: 32 (16 inputs + 16 outputs)
- Input Type: 24 VDC sink (X0–X17)
- Output Type: Transistor sink/NPN open-collector (Y0–Y17), 0.5 A per point, 5–30 VDC
- Memory Type: Flash ROM (battery-less, non-volatile)
- Battery: None required
- High-Speed Pulse Output: Y0 and Y1 up to 100 kHz
- Power Supply: 100–240 VAC, 50/60 Hz
- Program Memory: 64,000 steps (flash ROM)
- Execution Speed: 0.065 µs per LD instruction
- Built-in High-Speed Counters: 6 inputs (100 kHz)
- Communication: RS-422 (built-in)
- Real-Time Clock: Built-in (RTC battery still required for clock retention)
- Expansion: Up to 8 extension units, up to 4 special adapters
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 150 mm × 90 mm × 87 mm
- Weight: Approx. 0.80 kg
Typical Industrial Applications
The FX3U-32MT-LT-2 is deployed in applications where the elimination of battery maintenance delivers significant operational or economic benefits. In remote pump station automation for water and wastewater utilities, FX3U-32MT-LT-2 controllers manage pump start/stop logic, level monitoring, and SCADA communication at unmanned stations visited for maintenance only quarterly or annually — a battery failure in a standard FX3U between visits would cause program loss and require an emergency site visit to reprogram the controller, while the LT-2’s flash ROM retention prevents this scenario entirely. In solar power plant string monitoring and inverter control, the FX3U-32MT-LT-2 provides control logic for remote tracker arrays where the PLC cabinet internal temperature regularly exceeds 50°C under solar exposure — a temperature at which standard FX3U lithium batteries have a service life of less than 18 months, requiring twice-yearly battery replacement, while the LT-2 operates indefinitely without battery service. Marine vessel automation in harsh salt-air environments uses the FX3U-32MT-LT-2 because lithium batteries are sensitive to the humidity and temperature extremes of marine engine rooms and topside installations, and battery replacement at sea is logistically problematic. In vending machine and unattended kiosk control, the FX3U-32MT-LT-2 eliminates the service call required when a standard FX3U loses its program after a battery failure between scheduled maintenance visits.
Replacement & Upgrade Notes
The FX3U-32MT-LT-2 is a direct physical and electrical replacement for the FX3U-32MT/ESS in all applications — the same I/O count, output type, communication interfaces, and expansion architecture apply. The program developed for the FX3U-32MT/ESS transfers directly to the FX3U-32MT-LT-2 without modification. When migrating from the FX3U-32MT/ESS to the FX3U-32MT-LT-2 in an existing installation, note that while the FX3U-32MT-LT-2 eliminates the program memory battery, the base unit still contains a smaller RTC (real-time clock) battery for clock timekeeping — this smaller battery has a longer service life (typically 10+ years) than the main program retention battery, but should be included in extended maintenance planning. For applications currently using the FX3U-32MT/ESS with frequent battery changes due to high ambient temperature (above 45°C), the FX3U-32MT-LT-2 provides immediate relief from this maintenance burden — the flash ROM program retention performs consistently regardless of ambient temperature, without the exponential life reduction that lithium batteries experience above 40°C. The «LT» battery-less architecture is not available for all FX3U I/O variants — the FX3U-32MT-LT-2 is the primary battery-less transistor sink output model; for relay output or larger I/O count battery-less requirements, the FX3U-CF-ADP CompactFlash adapter with the FX3U-FLROM-1M can provide a similar program backup capability on standard FX3U relay output base units.
Frequently Asked Questions
Q: Can the FX3U-32MT-LT-2 retain D register data (process variables, counters) during power outages without a battery?
A: Designated D registers (configured as latched/non-volatile via GX Works2 parameter settings) are stored in flash ROM on the FX3U-32MT-LT-2, providing battery-less data retention for these registers during power outages. Non-designated (non-latched) D registers are cleared at power-up as on standard FX3U models. The distinction between latched and non-latched D registers is configured in GX Works2’s PLC parameter settings under the device tab — specify the range of D registers that should retain their values across power cycles, and the FX3U-32MT-LT-2’s flash ROM controller will automatically save these registers to flash at each program scan.
Q: Does the FX3U-32MT-LT-2 have any limitations compared to the standard FX3U-32MT/ESS in terms of programming or performance?
A: The FX3U-32MT-LT-2 is functionally identical to the FX3U-32MT/ESS in all programming and performance respects — same instruction set, same execution speed, same expansion capabilities, and same communication interfaces. The only operational difference is the flash ROM write latency for latched D register updates: in the FX3U-32MT-LT-2, writing to a latched D register triggers a background flash ROM write that takes slightly longer than an SRAM write — in most applications this difference is imperceptible, but in high-frequency latched register update applications (more than 1,000 writes per second to the same register), the flash ROM write cycle endurance should be calculated to estimate the expected service life before flash block wear occurs.
Q: Is the real-time clock in the FX3U-32MT-LT-2 also battery-less?
A: No. The FX3U-32MT-LT-2’s real-time clock uses a separate small coin-cell battery for timekeeping during power outages — this RTC battery is different from and much longer-lived than the standard FX3U program memory battery. The RTC battery typically provides 10 or more years of clock retention and is not included in routine annual maintenance schedules. If the RTC battery is depleted, the clock will reset to a default time at power-up but the program and data memory remain intact in flash ROM, unaffected by RTC battery condition.
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