The FX2N-4AD is Mitsubishi Electric’s 4-channel analogue input special function module for the MELSEC FX2N compact PLC series, providing four independent channels of 12-bit analogue-to-digital conversion with software-configurable input ranges — the most widely installed analogue input module in the FX2N platform, found in thousands of active FX2N-based process monitoring, PID temperature control, and multi-variable measurement applications worldwide. Unlike the FX2N-2AD’s hardware rotary switch range selection, the FX2N-4AD configures each channel’s input range via buffer memory writes from the FX2N ladder program, enabling remote range changes and multi-range channel mixing without physical module access. Atlantech Drives holds stock of the FX2N-4AD. Contact us for fast worldwide delivery and competitive pricing.
What Is the FX2N-4AD?
The FX2N-4AD is a MELSEC FX2N series special function module providing four channels of analogue input with 12-bit resolution and software-configurable input ranges. The module installs in the FX2N extension bus and communicates with the FX2N CPU via FROM/TO buffer memory instructions — the FX2N program writes channel range settings to the FX2N-4AD’s control registers using TO instructions at power-up (or from GX Works2’s special function module parameter write function), and reads converted analogue values from the measurement result registers using FROM instructions each scan cycle. Four channels of independent analogue measurement provide sufficient inputs for the most common multi-variable process monitoring applications: measuring four thermocouple transmitter outputs for multi-zone temperature monitoring, reading pressure, flow, level, and temperature transmitters for process control, or monitoring four axis positions from linear potentiometer transducers in a multi-axis positioning verification system. The FX2N-4AD supports both thermocouple and resistance thermometer (RTD) input via dedicated sub-models — the FX2N-4AD-TC accepts type K, J, T, and E thermocouples directly, while the FX2N-4AD-PT accepts Pt100 RTDs directly — providing complete temperature measurement from sensor to digital value without external signal conditioners when these sub-variants are specified.
Key Technical Specifications
- Model: FX2N-4AD
- Analogue Input Channels: 4
- Resolution: 12-bit (4,095 divisions unipolar; signed 12-bit for bipolar)
- Input Range (Voltage): 0–5 VDC, 0–10 VDC, -10 to +10 VDC (software configurable per channel)
- Input Range (Current): 4–20 mA (software configurable per channel)
- Input Accuracy: ±1% of full scale at 25°C
- Conversion Speed: Approx. 6 ms per channel (24 ms for all 4 channels)
- Extension Bus Occupation: 8 I/O points
- Special Sub-variants: FX2N-4AD-TC (thermocouple direct input), FX2N-4AD-PT (Pt100 RTD direct input)
- External Power Supply: 24 VDC ±10%, 55 mA (required)
- Operating Temperature: 0°C to 55°C
- Compatible FX2N base units: All FX2N models
- Weight: Approx. 0.18 kg
Compatibility & System Integration
The FX2N-4AD is compatible with all FX2N base units and integrates with GX Works2 and the legacy GX Developer for buffer memory parameter configuration and online channel monitoring. The module’s software-configurable range architecture enables each of the four channels to be assigned a different input type — for example, channel 1 configured for 4–20 mA from a pressure transmitter, channel 2 for 0–10 VDC from a position potentiometer, and channels 3 and 4 for 4–20 mA from flow transmitters — all from the same module without hardware modification. For PID temperature control applications using the FX2N-4AD alongside the FX2N base unit’s built-in PID instruction, the measured analogue value from the FX2N-4AD (read via FROM instruction to a D register) is used directly as the process variable input to the PID calculation, with the PID output written to an FX2N-4DA analogue output module for the manipulated variable. This FX2N-4AD + FX2N-4DA + PID instruction combination constitutes the standard FX2N closed-loop process control architecture used in thousands of active installations. The FX2N-4AD-TC thermocouple sub-variant simplifies installation in temperature measurement applications by eliminating external signal conditioning transmitters — type K, J, T, or E thermocouples connect directly to the FX2N-4AD-TC input terminals with built-in cold junction compensation, reducing installation cost and eliminating the transmitter as a potential failure point. The FX2N-4AD is also compatible with the FX2N-4LC temperature control module architecture for comparative reference — the FX2N-4LC integrates thermocouple input and PID output in a single module, while the FX2N-4AD provides the measurement function separately from the output function.
Installation Advice
The FX2N-4AD requires an external 24 VDC supply at 55 mA for its analogue input circuit — unlike the FX2N-2AD which draws power entirely from the FX2N base unit bus. Connect the external 24 VDC supply to the dedicated power terminals on the FX2N-4AD before applying power to the FX2N base unit — powering the base unit before the FX2N-4AD’s external supply causes the module to initialise with the analogue circuit unpowered, resulting in all channels reading zero regardless of input signal. Write the channel range configuration TO instructions in the FX2N program’s initialisation section (using M8002 — the first-scan pulse — to trigger the TO write) rather than writing the range configuration in the normal scan — the range configuration only needs to be written once at power-up, and continuous TO writes to the range register each scan consume unnecessary scan time and cause unnecessary flash write cycles in the module’s non-volatile range storage. For current input (4–20 mA) channels connected to two-wire loop-powered transmitters, use a separate 24 VDC supply for the transmitter loop power that is different from the FX2N-4AD’s external 24 VDC power supply terminal — sharing the same 24 VDC supply for both purposes with a common ground creates a ground loop path that introduces 50/60 Hz interference into the current measurement. Verify that the transmitter’s loop supply is compliant with the transmitter manufacturer’s minimum compliance voltage specification — the FX2N-4AD’s 250 Ω shunt resistor drops 5 V at 20 mA full scale, requiring the loop supply to provide at least the transmitter’s minimum operating voltage plus 5 V plus the cable resistance voltage drop.
Frequently Asked Questions
Q: Can all four channels of the FX2N-4AD be configured for different input ranges simultaneously?
A: Yes. Each of the four channels has an independent range configuration register in the FX2N-4AD’s buffer memory (BFM#0 for channel 1 range, BFM#1 for channel 2 range, etc.). Writing different range codes to each channel’s configuration register via TO instructions enables simultaneous operation of all four channels at different input ranges. For example, BFM#0 = K1 (4–20 mA), BFM#1 = K3 (0–10 VDC), BFM#2 = K1 (4–20 mA), BFM#3 = K2 (0–5 VDC) configures all four channels for different input types simultaneously.
Q: What is the FX2N-4AD buffer memory address for reading channel 1’s converted value?
A: The FX2N-4AD stores converted channel values in buffer memory from BFM#5 (channel 1 current value) through BFM#8 (channel 4 current value). The FROM instruction syntax for reading channel 1 to D10 is: FROM K0 K5 D10 K1 — where K0 is the module number (0 for the first special function module in the extension bus, incrementing by 1 for each additional module), K5 is the buffer memory number (BFM#5), D10 is the destination data register, and K1 is the number of words to read. Always verify the module number (K0, K1, K2, etc.) corresponds to the FX2N-4AD’s actual position in the extension bus — incorrect module numbers cause the FROM instruction to read the wrong module’s buffer memory.
Q: Does the FX2N-4AD provide any averaging function to reduce input noise?
A: Yes. The FX2N-4AD supports a built-in averaging function that averages a configurable number of consecutive conversion results (1 to 4,096 samples) before reporting the averaged value to BFM#5–8. The averaging count is configured by writing the desired sample count to BFM#0 (average count register) via a TO instruction. Increasing the averaging count reduces noise at the expense of increased response time — an averaging count of 10 introduces approximately 60 ms of response delay (10 samples × 6 ms per channel) but significantly reduces 50/60 Hz noise influence on the reported value.
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