Unisolated AS-interface bus application

AN2482

10/18

3

Unisolated AS-interface bus application

3.1

Application overview

The AS-Interface bus is a low-end field bus for actuators and sensors in manufacturing and

industrial automation. Its electrical architecture uses an unshielded 2-wire yellow cable that

transports both the 24 V power supply of the field nodes and the serial bidirectional data

communication.

Figure 11.

Simplified architecture of AS-interface Bus

The data communication is achieved with a current carrier modulation superimposed over

the power wires. Therefore, the power bus terminals are filtered in order to maintain identical

and calibrated differential and common mode impedances measured by both master and

slave units.

3.2

Isolation of the sensor section and the supply from

data/supply bus

The PCLT can be designed as an interface between a proximity sensor and its associated

slave controller unit.

The sensor power supply is generated from the bus power supply with a filter and a

regulator that are inserted in the slave unit. In the same manner, the sensor logic signal is

isolated from the AS-Interface power supply bus to avoid any degradation of the data

transmission.

A conventional way to achieve the interface with the PCLT and the AS-Interface controller is

to insert an opto-coupler between the AS-Interface controller and the PCLT that runs in

opto-coupler mode as shown on Figure 4. (MOD pin grounded).

I/O SLAVE

AS-i SLAVES

AS-i MASTER

I/O SLAVE

I/O SLAVE

I/O SLAVE

AS-i SLAVES

AS-i MASTER

I/O SLAVE

I/O SLAVE