Technical Description: Mitsubishi A1S38B Main Base Unit
The Mitsubishi A1S38B is a fundamental backplane component for the MELSEC-AnS and QnAS small-type modular PLC series. This main base unit serves as the physical and electrical backbone of the automation system, providing eight slots for the installation of CPU modules, I/O modules, and specialized functional blocks. While the AnS series is a legacy platform, it remains widely used in industrial plants globally due to its robust architecture and reliability in harsh environments.
High-Reliability Bus Architecture
The A1S38B provides a high-speed communication bus that facilitates seamless data exchange between the CPU and the various I/O modules. It includes a dedicated slot on the left for the power supply module (such as the A1S61PN), followed by eight slots for functional units. The base is designed for secure mounting within control panels, utilizing both screw-down points and DIN-rail compatibility. Its gold-plated bus connectors ensure low-resistance electrical paths, minimizing signal noise and maximizing system uptime over years of continuous operation.
Key Characteristics
- Part Number: A1S38B.
- Number of Slots: 8 Slots (for CPU and I/O modules).
- Series: MELSEC-AnS / QnAS.
- Mounting: Panel mount or DIN rail via adapter.
- Dimensions: 430 mm (Width) x 130 mm (Height).
- Material: Industrial-grade reinforced plastic and metal backplane.
- Current Consumption: 0.12 A (internal 5V DC).
- Compatibility: Compatible with all AnS series I/O and special modules.
System Versatility and Expansion
The A1S38B is often the starting point for complex control systems. If more than eight slots are required, this main base unit can be connected to extension base units (like the A1S65B or A1S68B) using specialized extension cables. This modularity allowed the AnS series to handle up to 1024 I/O points, a massive capacity for its footprint. Its rugged design ensures that the electronic modules are protected from mechanical stress and localized heat buildup.
| Category | Specification |
| Weight | Approx. 1.2 kg |
| Internal 5V Bus Current | Up to 5.0 A (Total load) |
| Standards | UL, CSA, CE (Ref. specific manufacturing date) |
Maintenance Insights
When maintaining an A1S38B system, always ensure that unused slots are covered with a blanking plate (A1SG60) to prevent dust ingress. Periodic inspection of the bus connector pins is recommended if modules are frequently swapped. The A1S38B is a passive component but is vital for the thermal stability of the entire PLC rack.
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