The FX3U-4LC is Mitsubishi Electric’s 4-channel temperature control module for the MELSEC FX3U compact PLC series, providing direct thermocouple and PT100 RTD input with integrated PID temperature control and analogue output generation for up to four independent temperature zones — delivering complete closed-loop temperature control without requiring separate signal conditioning, analogue input modules, or analogue output modules, in a single right-side extension module for any FX3U base unit. As the dedicated temperature control module for the FX3U platform, the FX3U-4LC enables injection moulding machine barrel temperature control, extruder zone control, oven temperature regulation, and multi-zone heat treatment automation from a compact FX3U system. Atlantech Drives holds stock of the FX3U-4LC. Contact us for fast worldwide delivery and competitive pricing.
What Is the FX3U-4LC?
The FX3U-4LC is a MELSEC FX3U series special function module — installed in the right-side FX3U extension bus — providing four independent channels of temperature measurement and PID closed-loop control. Each channel accepts either a thermocouple sensor (type K, J, R, S, B, E, T) or a PT100 resistance thermometer (3-wire) directly without external signal conditioning, and generates a proportional analogue output (voltage or current) to a heating or cooling actuator under PID control. The module executes the PID calculations autonomously in its own internal processor, independent of the FX3U CPU scan time — the CPU communicates setpoints and reads process values via FROM/TO buffer memory instructions, while the module manages the real-time control loop at a fixed 500 ms sampling interval. Built-in autotuning determines optimal P, I, and D parameters for each channel by executing a step response test on the controlled process, eliminating manual PID tuning calculations. The FX3U-4LC is functionally similar to the MELSEC-Q Q64TCRTN temperature control module but designed for the FX3U platform’s extension bus architecture and lower cost compact PLC applications.
Key Technical Specifications
- Model: FX3U-4LC
- Control Channels: 4 (independent PID per channel)
- Installation: FX3U right-side extension bus (occupies 32 I/O points)
- Input Type: Thermocouple (K, J, R, S, B, E, T) or PT100 RTD (3-wire) per channel
- Temperature Range: Thermocouple K: -200°C to +1372°C; PT100: -200°C to +850°C
- Input Resolution: 0.1°C
- Input Accuracy: ±0.5°C at 25°C (thermocouple); ±1.0°C (PT100)
- Control Algorithm: PID with autotuning
- Output Type: Voltage (0–5 VDC, 0–10 VDC) or Current (4–20 mA) per channel
- Output Resolution: 12-bit
- Sampling Period: 500 ms per channel
- Cold Junction Compensation: Built-in (thermocouple channels)
- Extension Bus Occupation: 32 I/O points
- External Power Supply: 24 VDC ±10%, 0.20 A (required)
- Current Consumption (FX3U bus): 0.08 A at 5 VDC
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.18 kg
Typical Industrial Applications
The FX3U-4LC is the standard temperature control module for FX3U-based machine control applications requiring multi-zone closed-loop temperature regulation. In injection moulding machines with four barrel heater zones, the FX3U-4LC independently controls each zone using thermocouple feedback and proportional valve or SSR (solid-state relay) output signals — the four PID controllers execute simultaneously at 500 ms sampling intervals, providing stable temperature regulation across all barrel zones without loading the FX3U CPU scan cycle with PID calculations. Plastic extrusion lines with four die zone heaters use the FX3U-4LC to maintain precise melt temperature profiles along the die body, where each zone requires independent PID tuning due to different thermal masses and heat transfer rates. Industrial ovens for powder coating, heat treatment, and food processing with separate heat-up, soak, and cool-down zones use the FX3U-4LC to manage zone temperature independently during each phase of the thermal cycle — the module’s autotuning function characterises the thermal response of each zone at commissioning, determining the optimal PID gains for each zone’s specific heat transfer dynamics. Small-scale chemical reactors in pharmaceutical and specialty chemical production use the FX3U-4LC for exothermic reaction temperature control, where the heating/cooling output drives both a heater and a cooling water valve in split-range control, with the FX3U-4LC generating separate heating and cooling analogue setpoints for the two actuators.
Expert Tips
When installing the FX3U-4LC alongside other extension modules in the FX3U extension bus, note that the module occupies 32 I/O points in the FX3U address space — verify that the total extension bus I/O address consumption (all extension modules combined) does not exceed the FX3U’s 256-point maximum. For the PID autotuning procedure, initiate autotuning from ambient temperature with the setpoint set to the normal operating temperature — running autotuning from an already-hot process at a setpoint close to the current temperature produces less reliable parameter estimates because the small temperature step change relative to setpoint provides insufficient signal-to-noise ratio for accurate process characterisation. For multi-zone injection moulding applications, perform autotuning on each zone sequentially rather than simultaneously — simultaneous autotuning on all four channels can cause thermal interaction between adjacent zones (heat conduction through the barrel) that distorts the step response on each individual zone. For thermocouple channels operating above 600°C, verify that the thermocouple cable and connectors are rated for the measurement temperature — standard compensating cable (lower temperature rating than the thermocouple itself) used in high-temperature applications can degrade rapidly and introduce measurement errors that appear as PID setpoint deviations without any other fault indication. Monitor the FX3U-4LC’s channel alarm registers via GX Works2 during initial commissioning to verify that no over-temperature or sensor break alarms are active before enabling the PID control outputs — proceeding with PID control while an alarm is active can cause runaway heating if the alarm is a sensor break that makes the measured temperature appear lower than actual.
Frequently Asked Questions
Q: Can the FX3U-4LC control cooling actuators as well as heating actuators?
A: Yes. The FX3U-4LC supports both heating-only and heating/cooling (split-range) control modes per channel. In heating/cooling mode, the analogue output represents both the heating demand (above the 50% midpoint) and the cooling demand (below the 50% midpoint) in a split-range output — the heating actuator is driven by the upper half of the analogue output range and the cooling actuator by the lower half, with independent P, I, and D gains configurable for the heating and cooling zones via buffer memory parameter registers. This mode is configured per channel via the FX3U-4LC’s buffer memory control mode register, accessible through GX Works2’s special function module parameter interface.
Q: What is the difference between the FX3U-4LC and the MELSEC-Q Q64TCRTN temperature control module?
A: Both modules provide 4-channel thermocouple/RTD input with autonomous PID temperature control and analogue output. The FX3U-4LC installs in the FX3U right-side extension bus and is configured for the compact FX3U platform, while the Q64TCRTN installs in the MELSEC-Q base unit slot. The Q64TCRTN supports additional thermocouple types (including N and PL II types not supported by the FX3U-4LC) and provides higher measurement accuracy (±0.3°C versus ±0.5°C). For FX3U-based systems, the FX3U-4LC is the correct specification; for MELSEC-Q systems requiring higher accuracy or additional sensor type support, the Q64TCRTN is appropriate.
Q: Can the FX3U-4LC be installed in the FX3U left-side special adapter bus?
A: No. The FX3U-4LC is a right-side extension module (not a left-side special adapter) and must be installed in the FX3U extension bus alongside I/O expansion modules. Left-side special adapters (FX3U-4AD-ADP, FX3U-4DA-ADP, FX3U-1PG) use a different physical connector and bus interface than right-side extension modules — the two module types are not interchangeable in terms of installation position.
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