The FX2N-2AD is Mitsubishi Electric’s 2-channel analogue input special function module for the MELSEC FX2N compact PLC series, providing two independent channels of 12-bit analogue-to-digital conversion for voltage and current signals — the entry-level analogue input module in the FX2N special function module range, widely installed in FX2N-based process monitoring and PID control applications that remain in active service globally. As a right-side extension bus module for the FX2N platform, the FX2N-2AD extends the FX2N base unit’s capabilities to include analogue process measurement from temperature transmitters, pressure sensors, flow meters, and position transducers with a minimum of hardware investment. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the FX2N-2AD?
The FX2N-2AD is a MELSEC FX2N series special function module providing two channels of analogue input signal conditioning and 12-bit analogue-to-digital conversion. The module installs in the FX2N extension bus (right side of the FX2N base unit) and communicates with the FX2N CPU via FROM/TO buffer memory instructions — the FX2N ladder program reads measured analogue values from the FX2N-2AD’s buffer memory using FROM instructions, with converted values stored as 12-bit integers (0–4095 for unipolar inputs, -2048 to +2047 for bipolar inputs). Each channel independently accepts voltage (0–5 VDC, 0–10 VDC, -10 to +10 VDC) or current (4–20 mA) input signals, with the input range for each channel selected via rotary switches on the module front panel rather than software configuration — a hardware selection approach that ensures the input range is preserved independently of the FX2N program. The module occupies 8 I/O points in the FX2N extension bus address space and draws power from the FX2N base unit’s internal bus supply, requiring no external power supply.
Key Technical Specifications
- Model: FX2N-2AD
- Analogue Input Channels: 2
- Resolution: 12-bit (4,095 divisions for unipolar; 4,096 divisions for bipolar)
- Input Range (Voltage): 0–5 VDC, 0–10 VDC, -10 to +10 VDC (rotary switch selection)
- Input Range (Current): 4–20 mA (rotary switch selection)
- Input Impedance (Voltage): 200 kΩ minimum
- Input Impedance (Current): 250 Ω
- Input Accuracy: ±1% of full scale at 25°C (±2% over full temperature range)
- Conversion Speed: Approx. 2.5 ms per channel (5 ms for both channels)
- Extension Bus Occupation: 8 I/O points
- External Power Supply: Not required (powered from FX2N bus)
- Operating Temperature: 0°C to 55°C
- Compatible FX2N base units: All FX2N models
- Weight: Approx. 0.15 kg
Series Comparison & Selection Guide
The FX2N analogue input module range covers three standard channel counts: the FX2N-2AD (2 channels), FX2N-4AD (4 channels), and FX2N-8AD (8 channels). All three modules provide 12-bit resolution and share the same FROM/TO buffer memory interface architecture, but differ in channel count, accuracy, and feature set. The FX2N-2AD is the simplest and lowest-cost option — appropriate when only two analogue measurements are required and when the hardware rotary switch channel configuration is acceptable. The FX2N-4AD provides four channels with software-configurable input ranges (via buffer memory writes) rather than hardware switches, offering more flexibility for installations where input range changes may be needed without physical module access. The FX2N-8AD provides eight channels with the highest accuracy in the FX2N analogue range (±0.5% versus ±1% for FX2N-2AD and FX2N-4AD) and software range configuration, making it the preferred choice for high-channel-count precision measurement applications. For new system designs, the FX3U-4AD-ADP left-side adapter (for FX3U base units) or the MELSEC-Q Q64AD module provide superior accuracy and software configurability compared to all FX2N analogue modules — the FX2N analogue modules are specified primarily for maintenance replacement of existing FX2N installations.
Troubleshooting Guide
If the FX2N-2AD returns incorrect or zero analogue values, the most common causes are incorrect rotary switch settings and incorrect FROM instruction addressing. Verify the rotary switch setting on the module front panel matches the connected signal type — if a 4–20 mA transmitter is connected but the rotary switch is set to 0–10 VDC voltage input mode, the module measures the voltage across its 250 Ω current input shunt resistor (approximately 1–5 V for a 4–20 mA signal) in voltage mode, returning an incorrect reading that appears partially correct but is not proportional to the actual process variable. Check the FROM instruction addressing in the GX Works2 ladder program — the FX2N-2AD buffer memory base address depends on the module’s position in the extension bus (the first extension module starts at a specific offset from the base unit, with each subsequent module’s address calculated based on the I/O points occupied by preceding modules). Use GX Works2’s special function module monitor to directly read the FX2N-2AD buffer memory addresses and verify the converted values before the FROM instruction is executed, isolating whether the fault is in the module conversion or in the ladder program addressing. For channel 2 returning values that appear to track channel 1 rather than the separate field input, verify the CH2 rotary switch is set to the correct input range — a channel 2 switch set to an unrecognised position causes the module to default to channel 1 mode behaviour on channel 2. Finally, check for 50/60 Hz noise coupling into voltage input channels — the FX2N-2AD does not have built-in digital filtering, so interference from adjacent VFD power cables can cause rapidly fluctuating readings that average incorrectly in the FX2N program. Implement a moving average filter in the FX2N ladder program to smooth high-frequency noise on affected channels.
Frequently Asked Questions
Q: Can the FX2N-2AD’s input range be changed in software via the FX2N program, or only via hardware rotary switch?
A: The FX2N-2AD’s input range selection is hardware-only via the rotary switches on the module front panel — there is no software method to change the input range from the FX2N program. This differs from the FX2N-4AD and FX2N-8AD, which support software input range configuration via buffer memory writes. To change the FX2N-2AD’s input range, power down the system, adjust the rotary switch to the new range setting, and power up again. For applications requiring remote or software-selectable input range changes, specify the FX2N-4AD instead.
Q: Does the FX2N-2AD provide any input disconnection detection for open-circuit 4–20 mA loops?
A: The FX2N-2AD does not provide dedicated disconnection detection circuitry or status flags for open-circuit input conditions. For 4–20 mA inputs, an open circuit results in the module reading 0 mA (0 counts at the digital output), which the FX2N ladder program can detect by monitoring for a converted value below the expected 4 mA minimum (approximately 0 counts versus the expected 800+ counts for a healthy 4 mA signal). Implement a low-value alarm in the FX2N program — if the converted value is below a threshold corresponding to approximately 3 mA, flag a sensor fault condition in the program logic.
Q: Can the FX2N-2AD be used with an FX3U base unit for replacement purposes?
A: The FX2N-2AD is an FX2N special function module and is not directly compatible with the FX3U base unit’s extension bus connector — FX2N special function modules use a different interface than FX3U extension modules. For FX3U systems requiring 2-channel analogue input, the FX3U-4AD-ADP left-side adapter or the FX3U-2AD main unit module (if available) are the appropriate FX3U-compatible alternatives. When migrating a complete FX2N system to FX3U, all FX2N special function modules including the FX2N-2AD must be replaced with FX3U-compatible equivalents.
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