The FX3U-16MT/ESS is Mitsubishi Electric’s 16-point transistor sink output base unit for the MELSEC FX3U compact PLC series, providing 8 digital inputs and 8 high-speed transistor sink (NPN) outputs in a self-contained AC-powered controller housing — combining the FX3U’s 0.065 µs instruction execution speed with transistor output switching for applications requiring fast output response, pulse train output for stepper and servo drives, and 24 VDC load control without the contact wear limitations of relay output models. As the transistor output complement to the FX3U-16MR/ES-A relay model, the FX3U-16MT/ESS is specified when output switching frequency exceeds relay capability, when direct pulse output to servo drives is required, or when output circuit longevity is a priority in high-cycle applications. Atlantech Drives holds stock of the FX3U-16MT/ESS. Contact us for fast worldwide delivery and competitive pricing.
What Is the FX3U-16MT/ESS?
The FX3U-16MT/ESS is a MELSEC FX3U series compact PLC base unit with transistor sink (NPN open-collector) outputs. The «T» in the model designation indicates transistor output type, and «SS» indicates sink output (NPN, common positive) with AC power supply input. The transistor outputs provide two critical capabilities not available with relay output models: first, high-speed switching at up to 100 kHz on designated high-speed output points (Y0 and Y1), enabling direct pulse train generation for stepper motor drivers and servo amplifiers with pulse input interfaces without requiring a separate positioning module. Second, unlimited electrical switching life — the transistor output has no mechanical wear components, making it suitable for applications where outputs switch thousands of times per hour continuously. The FX3U-16MT/ESS shares the same CPU, memory (64,000 steps), programming environment, and expansion architecture as the FX3U-16MR/ES-A — the only difference is the output type and associated output circuit specifications.
Key Technical Specifications
- Model: FX3U-16MT/ESS
- Total I/O Points: 16 (8 inputs + 8 outputs)
- Input Type: 24 VDC sink (X0–X7)
- Output Type: Transistor sink/NPN open-collector (Y0–Y7), 0.5 A per point, 5–30 VDC
- High-Speed Pulse Output Points: Y0 and Y1 (up to 100 kHz each)
- Power Supply: 100–240 VAC, 50/60 Hz
- Program Memory: 64,000 steps
- Execution Speed: 0.065 µs per LD instruction
- Built-in High-Speed Counters: 6 inputs (up to 100 kHz)
- Communication: RS-422 (built-in)
- Real-Time Clock: Built-in
- Battery Backup: Yes
- Expansion: Up to 8 extension units, up to 4 special adapter modules
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 90 mm × 90 mm × 87 mm
- Weight: Approx. 0.60 kg
Architecture & Design Overview
The FX3U-16MT/ESS implements the FX3U’s fourth-generation CPU architecture — the same processing core used in all FX3U base units regardless of output type — with the transistor output interface circuit replacing the relay driver stage of the MR model. The transistor output stage uses NPN open-collector power transistors, one per output point, with individual protection diodes against reverse voltage and resistor-limited base drive for controlled switching. The two designated high-speed output points (Y0 and Y1) use dedicated high-speed driver circuits that bypass the standard output refresh mechanism, allowing pulse generation at up to 100 kHz directly from the FX3U’s pulse output instructions (PLSY, DPLSY, PLSR) without scan time dependency. This built-in 2-axis pulse output capability enables the FX3U-16MT/ESS to control two axes of stepper or servo positioning directly — a single-phase stepper table indexer or a 2-axis Cartesian gantry — without any additional positioning module hardware. The remaining six output points (Y2–Y7) operate as standard transistor outputs refreshed each CPU scan cycle, with a maximum switching frequency limited by the scan time (typically 1–5 kHz for a 1–5 ms scan). The output circuit requires an external 24 VDC supply connected to the common terminal — the AC mains input powers only the CPU and input circuits; the output load power must be supplied externally.
Maintenance Tips
Unlike relay output models, the FX3U-16MT/ESS transistor outputs have no mechanical wear components and do not require periodic replacement based on switching cycle counts. However, transistor outputs are more susceptible to damage from inductive load switching without flyback protection than relay contacts. Inspect all inductive loads connected to the transistor outputs annually — verify that each inductive load (solenoid valve, relay coil, motor brake) has a flyback diode installed across the load terminals, with the diode cathode connected to the positive supply and the anode connected to the output terminal. A missing or failed flyback diode allows the inductive kickback voltage spike to reach the transistor output stage, potentially exceeding the output transistor’s maximum collector voltage (30 VDC rated) and causing latent damage that manifests as intermittent output failure weeks or months after the original overvoltage event. For output circuits driving capacitive loads (such as long cable runs to remote solenoid valves), add a series resistor of 10–22 Ω at the output terminal to limit the inrush current at the moment of output activation — capacitive inrush current exceeding the transistor’s rated 0.5 A instantaneous limit can cause transistor saturation delay that generates a timing error in high-speed applications. Check the output common terminal connection annually in high-vibration environments — a loose output common terminal causes all outputs in the common group to fail intermittently, which can be misdiagnosed as a CPU fault.
Frequently Asked Questions
Q: Can the FX3U-16MT/ESS generate a 2-axis coordinated motion profile for a simple XY table?
A: Yes, with limitations. The FX3U-16MT/ESS’s two high-speed pulse output points (Y0, Y1) can simultaneously generate independent pulse trains for two stepper or servo axes. The DPLSY instruction generates a pulse output at a fixed frequency (speed), and the DRVI/DRVA instructions generate relative/absolute position moves. However, the FX3U-16MT/ESS does not support interpolated 2-axis moves (diagonal straight lines) natively — each axis moves independently. For true 2-axis linear interpolation, the QD75D2 MELSEC-Q positioning module or the FX3U-20SSC-H special adapter must be used.
Q: What is the maximum stepper motor speed achievable using the FX3U-16MT/ESS pulse output?
A: The FX3U-16MT/ESS generates pulse output at up to 100 kHz on Y0 and Y1. For a standard 200-step stepper motor (1.8° step angle) with a driver configured for 1/4 microstepping (800 microsteps per revolution), the maximum speed is 100,000 ÷ 800 = 125 RPS = 7,500 RPM. For a driver configured for full-step mode (200 steps per revolution), the maximum speed is 100,000 ÷ 200 = 500 RPS = 30,000 RPM — far beyond the mechanical speed limit of any standard stepper motor. In practice, the usable maximum speed is limited by the stepper motor’s pull-out torque curve, typically 1,000–3,000 RPM for standard NEMA 17/23 frame motors under moderate load.
Q: Is the FX3U-16MT/ESS compatible with source (PNP) output devices, or only sink (NPN) input devices?
A: The FX3U-16MT/ESS inputs accept sink-wired (NPN, common positive) field devices — the input common terminal is connected to 24 VDC positive, and NPN sensors pull the input terminal low to signal ON. PNP (source output) sensors that push the input terminal high are not directly compatible with the sink input wiring of the ES/A models. For PNP sensor compatibility, the FX3U-16MT/ES (source input model, common negative) or an NPN-to-PNP signal converter should be specified.
Do you need more references from this brand? Explore our full catalog of Mitsubishi here: https://atlantechdrives.com/manufacturers/mitsubishi/
