FIELDBUSES
AS-Interface (AS-i)
Sensors and actuators share a two-wire cable for data and power.
Who communicates with whom?
In classical AS-i, the master initiates communication and selects a participant by its configured address. The addressed device returns input/status data, while other participants remain silent in that slot. Sending an output bit and receiving data does not prove a physical actuator moved: use suitable feedback or diagnostics. ASi-5 telegram details differ from earlier generations.
Voltage and waveform
AS-Interface carries power and data on the same two wires. Many installations use a dedicated decoupled supply around 30 V DC; some supplies are adjustable between roughly 24 and 30 V. Data appear as short alternating pulses superimposed on the DC component.
Measuring with an oscilloscope
Measure the DC supply between AS-i+ and AS-i− with a suitable meter. To view data, use a suitable differential or isolated scope measurement across the pair. AC coupling may help reveal the smaller pulse component while the DC supply is measured separately.
The principle
AS-Interface connects field devices to a controller over a shared two-wire cable. An AS-i master exchanges data with addressed participants. The cable may carry both data and power; the exact design depends on the AS-i generation and components.
An example
The demo addresses two participants in turn. It is a logical example, not exact telegram timing or a measured waveform.
Important
AS-i Safety needs dedicated safety components and procedures; an ordinary data connection is not itself a safety function.