H. Kuhnke Ltd, Romsey, UK
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Airbox. The Kuhnke Asi Pneumatic Slave Module

AS-i Introduction

Actuator Sensor Interface (AS-Interface) is a wiring system that connects power and signal (input & output) from a PLC to devices on a machine or process. In its basic form only one cable (a simple pair) runs from the PLC output/input card for up to 900 metres (with repeaters) connecting proximity switches, photo sensors, motor starters, push buttons, signal columns, solenoids, valves, switches etc.

More recently safety devices up to category 4 can be connected to the same networks.

Each of these field devices can have an integrated AS-Interface connection or be connected to an Input/Output node. One master PLC controls up to 31 (62 with AS-Interface 2.1) nodes and each node can be up to 4I/4O ( or 8 Inputs or 8 Outputs). So the maximum I/O per AS-Interface master is 248 (465 with AS-Interface 2.1). A master PLC will normally need a power supply, an AS-Interface output module, and possibly a communications module to interface with a higher fieldbus (e.g. Profibus or Devicenet) known as a gateway.

A control frequency is screened into the power supply pair which polls all 31 (62) nodes, and instructs outputs to switch high or low and inputs to report status high or low. This combined power & signal cable is normally yellow and can carry up to 7A. Removal of power is also removal of signal. Popular flat moulded self sealing two core cable is favoured for push fit vampire connections that reseal on removal (but any correct diameter 2 wires can carry AS-Interface power and signal).

Black cable (also flat, self seal and suitable for vampire pins) is used as an auxiliary power line. It requires a separate power supply module at the AS-Interface master, or locally. Black cable carries power only (24VDC). Here removal of power can be effected without removal of signal (yellow cable).

Kuhnke Airboxes can be supplied with either a yellow cable only or yellow and black cable connections.

 

The main advantage of AS-Interface is cabling and programming. To connect 465 I/O to a conventional PLC, at 2 cables per I/O could involve the preparation of 1860 cable ends, each with potentional for error on connection or tagging. AS-Interface avoids this completely - only two cable ends! Cable runs comprise one single flat cable (2 with black), no complex bundles.

A Kuhnke Airbox combines inputs and outputs at one node,enabling a single address code for individual actuators/cylinders. This makes programming, installations and fault finding more straight forward than valve island solutions.

AS-Interface is an "open" bus system. Any AS-Interface product of any manufacturer, is usable on any AS-Interface network. It is used as a "stand-alone" network, or as the final connection system of higher level bus systems such as PROFIBUS and DEVICENET. Users of more complex automation might have multiple AS-i networks each running as a unique PROFIBUS slave for example. Here the advantages of AS-i cabling are greater.

Kuhnke supply specialist pneumatic devices for use on any AS-Interface network. Only the the node address need be set on installation. Kuhnke products simply plug and play! We also supply a 6A output device, ideal for switching high loads. Suppliers of AS-Interface controllers generally will offer the plc (master), power supplies, cables and gateways to higher lever systems. AS-Interface stands for Actuator Sensor Interface and basically replaces the I/O (& I/O expansion) ports of a plc.

The real benefit of AS-Interface in pneumatic applications is to take the pneumatic valve (Airbox) back where it belongs as near to the actuator/cylinder as possible. With easy mounting & IP67 protection this is a very real alternative.

For more information on AS-i Safe and the latest versions of AS-i (version 3.0 was introduced in late 2005 with many new products coming to the market in the following years) we reccomend you visit AS-i Expert Alliance

Kuhnke publish an AS-Interface introduction (E704). Which you may find helpful. Please visit the download section.