The FX3U-3A-ADP is Mitsubishi Electric’s combined analogue input/output special adapter for the MELSEC FX3U compact PLC series, providing two channels of analogue input and one channel of analogue output in a single left-side adapter module — delivering basic analogue I/O capability to any FX3U base unit without occupying an extension bus position, at the lowest cost and most compact form factor of any FX3U analogue adapter. Designed for applications requiring simple analogue sensor reading and analogue setpoint generation alongside the FX3U’s digital I/O — such as temperature monitoring with 4–20 mA transmitters, pressure setpoint generation for proportional valves, and speed reference output to variable frequency drives — the FX3U-3A-ADP provides the essential analogue functions most compact PLC applications require in a single economical module. Atlantech Drives holds stock of the FX3U-3A-ADP. Contact us for fast worldwide delivery and competitive pricing.
What Is the FX3U-3A-ADP?
The FX3U-3A-ADP is a MELSEC FX3U series special function adapter module providing two analogue input channels and one analogue output channel in a combined unit. The two analogue input channels accept either voltage (0–5 VDC, 0–10 VDC, -10 to +10 VDC) or current (4–20 mA) signals from field transmitters, sensors, and measurement instruments, converting them to 12-bit digital values accessible in the FX3U’s buffer memory. The single analogue output channel converts a 12-bit digital value from the FX3U program to an analogue output signal in the configured range, suitable for driving variable frequency drive speed references (0–10 VDC or 4–20 mA), proportional valve controllers (4–20 mA), and analogue setpoint inputs on process controllers. 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 — dedicated analogue access instructions in the FX3U (VRRD for voltage reading, VRSC for current reading, VRSC for output) provide simplified access to the adapter without requiring manual buffer memory address programming in some application types.
Key Technical Specifications
- Model: FX3U-3A-ADP
- Analogue Input Channels: 2
- Analogue Output Channels: 1
- Input Resolution: 12-bit (0–4095 digital range)
- Input Range (Voltage): 0–5 VDC, 0–10 VDC, -10 to +10 VDC (selectable per channel)
- Input Range (Current): 4–20 mA (selectable per channel)
- Input Accuracy: ±1% of full scale at 25°C
- Output Resolution: 12-bit
- Output Range (Voltage): 0–5 VDC, 0–10 VDC (selectable)
- Output Range (Current): 4–20 mA (selectable)
- Output Accuracy: ±1% of full scale at 25°C
- Conversion Speed: Approx. 2.5 ms per input channel; 2 ms output update
- Connection Interface: FX3U left-side special adapter bus
- External Power Supply: 24 VDC ±10%, 0.05 A (required for analogue circuit)
- Current Consumption (adapter bus): 0.05 A at 5 VDC
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.09 kg
Compatibility & System Integration
The FX3U-3A-ADP is compatible with all FX3U base units and integrates with GX Works2 for buffer memory configuration and online monitoring. Up to four FX3U-3A-ADP adapters can be installed on the same FX3U base unit (one per left-side adapter position), providing up to 8 analogue inputs and 4 analogue outputs from adapters alone — supplemented by any FX3U-4AD-ADP (4 analogue input) or FX3U-4DA-ADP (4 analogue output) adapters installed in the remaining adapter positions for higher-channel-count configurations. The FX3U-3A-ADP’s combined input/output architecture makes it particularly cost-effective for applications requiring a small number of both input and output channels — a single FX3U-3A-ADP provides the analogue capability for a basic PID control loop (one process variable input, one manipulated variable output) plus one additional monitoring input, without the cost of separate input and output modules. For PID temperature control using the FX3U-3A-ADP, the FX3U base unit’s built-in PID instruction (PID) reads the process temperature from the FX3U-3A-ADP input buffer memory, calculates the control output using the PID algorithm, and writes the control output value to the output buffer memory for transmission to the FX3U-3A-ADP analogue output — a complete software PID controller using only the base unit and a single adapter module. For applications requiring higher analogue accuracy than the FX3U-3A-ADP’s ±1% specification, the FX3U-4AD-ADP (input only, ±0.5% accuracy) or the MELSEC-Q Q64AD (16-bit, ±0.1% accuracy) should be specified instead.
Troubleshooting Guide
If the FX3U-3A-ADP analogue input channels read incorrect or unstable values, verify first that the external 24 VDC power supply is connected to the adapter’s power terminals and is within the 21.6–26.4 VDC operating range — the analogue input circuit is powered exclusively by the external 24 VDC supply, and a missing or out-of-range supply causes all analogue channels to read incorrect values or zero. For current input channels (4–20 mA), verify that the connected transmitter’s loop supply is not shared with the FX3U-3A-ADP’s external power supply in a configuration that creates a ground loop — if both the transmitter and the adapter share the same 24 VDC supply with a common ground connection at the panel, the 4–20 mA loop may carry interference from other devices on the same supply rail. Use a separate 24 VDC supply for the FX3U-3A-ADP’s analogue power terminal if ground loop interference is suspected. For voltage input channels reading values lower than expected, check the input wiring for high-resistance connections — a 100 Ω contact resistance in a 0–10 VDC voltage input circuit with a transmitter output impedance of 100 Ω will cause a 50% voltage divider effect, halving the measured voltage. Verify all input terminal connections are tight and free of corrosion. For the analogue output channel generating no signal despite the program writing a non-zero digital value to the output buffer memory, confirm that the FX3U program has correctly enabled the output channel via the output enable buffer memory register — the output channel defaults to disabled at power-up and must be explicitly enabled by the ladder program before any analogue output is generated.
Frequently Asked Questions
Q: Can the FX3U-3A-ADP’s two analogue input channels be configured for different input types simultaneously?
A: Yes. Each of the two input channels is independently configurable for voltage or current input mode via the channel range setting in the adapter’s buffer memory, accessible through GX Works2’s special adapter parameter editor. Channel 1 can be configured for 4–20 mA current input while channel 2 is configured for 0–10 VDC voltage input, without any interaction between the two channels.
Q: What is the minimum recommended FX3U scan time for stable analogue readings from the FX3U-3A-ADP?
A: The FX3U-3A-ADP updates each input channel approximately every 2.5 ms — both channels complete a full conversion in approximately 5 ms. For stable FX3U program readings, the FX3U scan time should be at least 10 ms (two to three times the adapter conversion cycle) to ensure the program is reading a freshly converted value rather than the same value read in the previous scan. For FX3U scan times shorter than 5 ms, use GX Works2’s input filter setting to average multiple consecutive readings before presenting the value to the FX3U D register, reducing reading noise at the expense of increased response time.
Q: Can the FX3U-3A-ADP output a 0–10 VDC signal to control a Mitsubishi FR-E840 inverter speed reference?
A: Yes. The FX3U-3A-ADP’s analogue output channel can be configured for 0–10 VDC output and connected directly to the FR-E840’s frequency setting input (terminal 2 for voltage input, terminal 5 for 0 V common). Set the FR-E840’s Pr.73 (analogue input selection) to the 0–10 VDC voltage input mode, and the inverter will vary its output frequency proportionally to the 0–10 VDC signal from the FX3U-3A-ADP — providing a complete compact drive control system with the FX3U managing the speed profile logic and the FR-E840 implementing the motor drive.
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