The FX3U-4AD-ADP is Mitsubishi Electric’s 4-channel analogue input special adapter for the MELSEC FX3U compact PLC series, providing four independent channels of 12-bit analogue-to-digital conversion for voltage and current signals — delivering higher channel count analogue input capability than the FX3U-3A-ADP combined module, with dedicated input-only architecture optimised for applications requiring four simultaneous analogue measurements from a single left-side adapter without occupying any FX3U extension bus capacity. As the standard analogue input adapter for FX3U systems requiring monitoring of four process variables — temperature transmitter outputs, pressure sensor signals, flow meter outputs, and position transducer signals — the FX3U-4AD-ADP integrates directly into the FX3U platform with GX Works2 configuration and buffer memory access. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the FX3U-4AD-ADP?
The FX3U-4AD-ADP is a MELSEC FX3U series special function adapter module providing four channels of analogue input signal conditioning and 12-bit analogue-to-digital conversion. Each channel independently accepts either voltage (0–5 VDC, 0–10 VDC, -10 to +10 VDC) or current (4–20 mA, 0–20 mA) input signals from field transmitters and sensors, with the input range for each channel configured independently via GX Works2 buffer memory parameter settings. The 12-bit resolution provides 4,096 digital levels over the configured input range — for a 4–20 mA input, this corresponds to a minimum current resolution of approximately 3.9 µA, adequate for all standard industrial process measurement applications. The adapter connects to the FX3U base unit’s left-side special adapter interface and communicates with the CPU via the buffer memory FROM/TO instruction interface, with measured analogue values stored in dedicated buffer memory registers updated every 6 ms per adapter (1.5 ms per channel at 4 channels active). The FX3U-4AD-ADP is the input-only counterpart to the FX3U-4DA-ADP output adapter, and both can be installed simultaneously on the same FX3U base unit in adjacent adapter positions for combined 4-input/4-output analogue capability.
Key Technical Specifications
- Model: FX3U-4AD-ADP
- Analogue Input Channels: 4
- Resolution: 12-bit (4,095 divisions)
- Input Range (Voltage): 0–5 VDC, 0–10 VDC, -10 to +10 VDC (per channel)
- Input Range (Current): 4–20 mA, 0–20 mA (per channel)
- Input Impedance (Voltage): 200 kΩ minimum
- Input Impedance (Current): 250 Ω
- Input Accuracy: ±0.5% of full scale at 25°C (±1.0% over full temperature range)
- Conversion Speed: Approx. 1.5 ms per channel (6 ms total for 4 channels)
- Isolation: Optical, between field inputs and adapter bus
- Connection Interface: FX3U left-side special adapter bus
- External Power Supply: 24 VDC ±10%, 0.05 A (required)
- Current Consumption (adapter bus): 0.07 A at 5 VDC
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.10 kg
Series Comparison & Selection Guide
The FX3U analogue input adapter range offers three options with different channel counts and accuracy levels. The FX3U-3A-ADP (2 inputs + 1 output, ±1% accuracy) is the most cost-effective choice for applications requiring a minimal analogue interface with both input and output in a single module. The FX3U-4AD-ADP (4 inputs only, ±0.5% accuracy) provides double the input channel count with improved accuracy compared to the FX3U-3A-ADP, making it the standard choice for process monitoring applications requiring four independent measurements. The FX3U-4AD (main unit analogue module, rather than adapter) provides 4 inputs with 12-bit resolution at higher current consumption and right-side extension bus installation. For applications requiring more than four analogue inputs, multiple FX3U-4AD-ADP adapters can be installed in adjacent adapter positions (up to four adapters total), providing up to 16 analogue input channels from adapters alone. When comparing the FX3U-4AD-ADP adapter to the MELSEC-Q Q64AD analogue input module: the FX3U-4AD-ADP provides 12-bit resolution at ±0.5% accuracy, while the Q64AD provides 16-bit resolution at ±0.1% accuracy — for applications where measurement accuracy better than 0.5% is required, the MELSEC-Q platform with Q64AD is the appropriate specification rather than FX3U with FX3U-4AD-ADP.
Installation Advice
When wiring the FX3U-4AD-ADP for current input (4–20 mA) measurements, verify the transmitter loop wiring configuration before connecting — the FX3U-4AD-ADP current input circuit is a passive 250 Ω shunt resistor that measures the voltage drop across the shunt to determine the loop current. This circuit requires the 4–20 mA transmitter to supply the loop current from its own 24 VDC loop power supply, with the FX3U-4AD-ADP shunt resistor inserted in series in the loop. Do not connect two-wire loop-powered transmitters to the FX3U-4AD-ADP current input without verifying that the transmitter’s 24 VDC loop supply is separate from the FX3U-4AD-ADP’s external 24 VDC adapter power supply — sharing the same 24 VDC supply for both purposes with a common ground connection creates a ground loop that introduces 50/60 Hz noise into the current measurement. For voltage input channels connected to sensors with high-impedance outputs (such as pH electrodes or thermocouple millivolt signals without signal conditioning), buffer the sensor output with a signal conditioner or transmitter before connecting to the FX3U-4AD-ADP — the adapter’s 200 kΩ input impedance is adequate for most standard voltage transmitters but not for high-impedance electrode-type sensors. Shield all analogue input cables and connect the shield to earth at the FX3U-4AD-ADP terminal end only (single-point earthing) to prevent earth loop interference from VFDs and other electromagnetic noise sources in the control panel.
Frequently Asked Questions
Q: Can the FX3U-4AD-ADP accept thermocouple signals directly without a signal conditioner?
A: No. Thermocouple signals are millivolt-level (typically 0–50 mV for a type K thermocouple over a 0–1200°C range), far below the FX3U-4AD-ADP’s minimum voltage input range of 0–5 VDC. Thermocouples must be connected to a thermocouple transmitter or signal conditioner that amplifies and cold-junction-compensates the millivolt signal to a standard 4–20 mA or 0–10 VDC output before connecting to the FX3U-4AD-ADP. For direct thermocouple or RTD connection without external signal conditioning, the FX3U-4LC temperature control adapter supports direct thermocouple and PT100 RTD input with built-in signal conditioning and PID control.
Q: How do multiple FX3U-4AD-ADP adapters coexist on the same FX3U base unit?
A: Up to four FX3U-4AD-ADP adapters can be installed in the four left-side adapter positions of any FX3U base unit. Each adapter occupies one adapter position and is assigned a unique buffer memory address range based on its position number (position 1 closest to the base unit). GX Works2’s special adapter configuration tool automatically assigns the correct buffer memory base addresses for each adapter based on its configured position, and each adapter’s channel data is accessed using position-specific FROM/TO instructions in the FX3U ladder program.
Q: Does the FX3U-4AD-ADP provide input disconnection detection for open-circuit 4–20 mA loops?
A: Yes. In 4–20 mA input mode, the FX3U-4AD-ADP monitors the input current and sets a disconnection detection flag in the buffer memory if the measured current falls below 2 mA — the minimum threshold indicating an open circuit or transmitter failure. The FX3U ladder program monitors this flag via a FROM instruction and can initiate an alarm or safe-state sequence when a transmitter disconnection is detected. The disconnection detection response time is within two conversion cycles (approximately 3 ms) of the fault occurring.
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