Mitsubishi A1SX81 32-Point Digital Input Module (MELSEC A Series)
The Mitsubishi A1SX81 is a DC input module for the MELSEC A series programmable logic controller family. It provides 32 discrete input points for connecting push buttons, limit switches, proximity sensors, and other 24 V DC devices. The module occupies one slot in an A series base unit (e.g., A1S38B, A1S68B).
Electrical Specifications
Input type: DC 24 V (sink/source common). Rated input voltage: 24 V DC (20.4-28.8 V). Input impedance: 4.7 kΩ. ON voltage: >15 V DC (2.5 mA min). OFF voltage:<5 V DC (1.0 mA max). Response time: 1 ms (OFF→ON and ON→OFF) adjustable via PLC parameter. The module has 2 common terminals (each common serves 16 inputs). Current consumption from backplane: 50 mA (5 V DC). Isolation: opto-coupler between field and internal bus.
Indicators and Wiring
Each input has a green LED indicator on the front panel that lights when the input is active. The module includes a 40-pin connector (Mitsubishi FX-40P or equivalent) for wiring. A removable terminal block adapter (e.g., A6TB-36E) is available for screw termination. The input address assignment (X0 to X1F) is based on the slot position. The module supports both sink (NPN) and source (PNP) configurations by connecting the common terminal to -24 V or +24 V respectively.
Environmental and Mechanical
Dimensions: 130 mm x 34.5 mm x 90 mm (H x W x D). Weight: 0.25 kg. Operating temperature: 0°C to 55°C. Storage: -20°C to 75°C. Humidity: 10% to 90% non-condensing. Vibration: 2 g (10-57 Hz). The module is rated IP20. It meets CE and UL 508. The case is made of flame-retardant plastic (UL94 V-0).
Compatibility and Applications
The A1SX81 is compatible with all A series CPUs: A1S, A2S, A3S, and AnSH. It can be used in both main base and extension base units. Typical inputs include emergency stops (after safety relay), part present sensors, conveyor jam detectors, and cycle start buttons. The 32-point density is ideal for machine control with high I/O count but limited panel space. For systems requiring 16 points, the A1SX41 is a smaller alternative.
Maintenance and Replacement
No calibration required. Periodic cleaning of the connector contacts with isopropyl alcohol is suggested in dusty environments. Replacement module: identical base part number (A1SX81). For modern upgrades, the Mitsubishi Q series (e.g., QX81) can be adapted with a conversion base. The input response time can be changed in the PLC’s parameter to filter noise (0.5 to 15 ms).
