What is AS-Interface?
AS-Interface (full name: Actuator Sensor Interface, also known as AS-i) is a simple and cost-effective fieldbus protocol for connecting Sensors and Actuators at the lower levels of an automation system.
It is often used as the underlying layer within larger systems such as Profibus, ProfiNET or Ethernet IP.
🧠 What does AS-Interface do?
AS-i connects binary Sensors and Actuators (such as pushbuttons, light barriers, valves and motor starters) over a single two-wire cable that carries both data and power.
It is mainly intended for:
- Simple signals (on/off)
- Quick installation
- Cost savings on wiring
🔧 Key features of AS-Interface
| Feature | Description |
|---|---|
| Topology | Free (line, ring, star) without termination |
| Cabling | Just two wires for data and power (yellow flat cable) |
| Number of nodes | Up to 62 devices per network (extendable with repeaters/gateways) |
| Signal type | Digital (binary, 0/1), occasionally analogue via modules |
| Cycle time | Up to 5 ms for 31 nodes |
| Integration | Connects to higher-level networks via gateways (Profibus, ProfiNET) |
📦 Example applications
- Conveyor systems: position sensors, start/stop buttons
- Packaging machines: detection of boxes, bottles or labels
- Warehouse automation: limit switches and photocells
- Automotive: assembly lines with many decentralised signals
🔄 AS-Interface vs. other fieldbuses
| Aspect | AS-Interface | Profibus | EtherCAT |
|---|---|---|---|
| Complexity | Very low | Medium | High |
| Target | Sensor/Actuator (low-level) | Broad automation | Motion Control and real-time I/O |
| Cabling | 2-wire, data + power | Separate power + twisted pair | Ethernet + separate power |
| Cycle time | Very fast for simple signals | Faster for complex communication | Very fast and deterministic |
| Max. nodes | 62 per network | 126 per segment | > 65,000 |
📌 In summary
AS-Interface is a simple and inexpensive fieldbus for connecting Sensors and Actuators on the factory floor. It minimises wiring, is easy to install and serves as a solid base layer beneath more advanced systems.